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Information Sensors
All of the sensors and the input switches can be diagnosed through the use of a scan tool. The following is a shortdescription of how the sensors and switches can be diagnosed by using a scan tool. The scan tool can also be used in
order to compare the values for a normal running engine with the engine being diagnosed.
Engine Coolant Temperature (ECT) Sensor
(1) ECT Electrical Connector
(2) Connector Tab
(3) Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature sensor is a thermistor (a resistor which changes value based on temperature) mountethe engine coolant pump. Low coolant temperature produces a high resistance (100,000 ohms at -40C/-40F) while
high temperature causes low resistance (70 ohms at 130C/266F).
The PCM supplies a 5 volt signal to the engine coolant temperature sensor through a resistor in the PCM and measurthe voltage. The voltage will be high when the engine is cold. The voltage will be low when the engine is hot. Bymeasuring the voltage, the PCM calculates the engine coolant temperature. Engine coolant temperature affects most
systems the PCM controls.
The scan tool displays engine coolant temperature in degrees. After engine startup, the temperature should rise stead
to about 90C (194F) then stabilize when thermostat opens. If the engine has not been run for several hours(overnight), the engine coolant temperature and intake air temperature displays should be close to each other. When
PCM detects a malfunction in the ECT sensor circuit, the following DTCs will set:
DTC P0117 circuit low.
DTC P0118 circuit high. DTC P0125 excessive time to Closed Loop.
DTC P1114 circuit intermittent low.
DTC P1115 circuit intermittent high.
Service Category Specifications contains a table to check for sensor resistance values relative to temperature.
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Mass Air Flow (MAF) Sensor
The Mass Air Flow (MAF) sensor measures the amount of air which passes through it. The PCM uses this informatioto determine the operating condition of the engine, to control fuel delivery. A large quantity of air indicates
acceleration. A small quantity of air indicates deceleration or idle.
The scan tool reads the MAF value and displays it in grams per second (gm/Sec). At idle, it should read between
6 gm/Sec - 9 gm/Sec on a fully warmed up engine. Values should change rather quickly on acceleration, but valuesshould remain fairly stable at any given RPM. When the PCM detects a malfunction in the MAF sensor circuit, the
following DTCs will set:
DTC P0100 circuit malfunction.
DTC P0101 system performance.
DTC P0102 frequency low. DTC P0103 frequency high.
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Intake Air Temperature (IAT) Sensor
(1) Intake Air Temperature (IAT) Sensor
(2) Electrical Harness Connector
The Intake Air Temperature (IAT) sensor is a thermistor which changes value based on the temperature of air enterin
the engine. Low temperature produces a high resistance (100,000 ohms at -40C/-40F). A high temperature causes resistance (70 ohms at 130C/266F). The PCM supplies a 5.0 volt signal to the sensor through a resistor in the PCM
and measures the voltage. The voltage will be high when the incoming air is cold, and low when the air is hot. By
measuring the voltage, the PCM calculates the incoming air temperature. The IAT sensor signal is used to adjust spatiming according to incoming air density.
The scan tool displays temperature of the air entering the engine, which should read close to ambient air temperature
when engine is cold. The temperature should rise as underhood temperature increases. If the engine has not been run
several hours (overnight) the IAT sensor temperature and engine coolant temperature should read close to each otherthe PCM detects a malfunction in the IAT sensor circuit, the following DTCs will set:
DTC P0112 circuit low.
DTC P0113 circuit high.
DTC P1111 circuit intermittent high.
DTC P1112 circuit intermittent low.
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Manifold Absolute Pressure (MAP) Sensor
(1) Electrical Connector(2) Manifold Absolute Pressure (MAP) Sensor
The Manifold Absolute Pressure (MAP) sensor responds to changes in the intake manifold pressure. The pressurechanges as a result of engine load and speed. The map sensor converts this to a voltage output.
A closed throttle on engine coast down would produce a relatively low map output voltage. A wide open throttle wou
produce a high map output voltage. This high output voltage is produced because the pressure inside the manifold issame as outside the manifold. The MAP is inversely proportional to what is measured on a vacuum gage. The MAP
sensor is used for the following:
Altitude determination. Ignition timing control.
EGR diagnostic.
Speed density fuel management default.
When the PCM detects a malfunction in the MAP sensor circuit, the following DTCs will set:
DTC P0106 circuit performance malfunction.
DTC P0107 circuit low.
DTC P0108 circuit high.
DTC P1107 intermittent circuit low.
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Heated Oxygen Sensors (HO2S) cutaway
(1) Four Wire In-Line Connector
(2) Heater Termination
(3) Water Shield Assembly
(4) Sensor Lead(5) Flat Seat Shell
(6) Seat Gasket
(7) Outer Electrode and Protective Coating
(8) Rod Heater
(9) Inner Electrode
(10) Zirconia Element
(11) Insulator
(12) Clip Ring
(13) Gripper
Front Heated Oxygen Sensors (HO2S)
The heated oxygen sensors (HO2S) are mounted in the exhaust system where they can monitor the oxygen content o
the exhaust gas stream. The oxygen present in the exhaust gas reacts with the sensor to produce a voltage output. Thi
voltage should constantly fluctuate from approximately 100 mV (high oxygen content - lean mixture) to 900 mV (looxygen content - rich mixture). The heated oxygen sensor voltage can be monitored with a scan tool. By monitoring
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voltage output of the oxygen sensor, the PCM calculates what fuel mixture command to give to the injectors (lean
mixture - low HO2S voltage = rich command, rich mixture - high HO2S voltage = lean command).
When the PCM detects an HO2S signal circuit that is low, the PCM will set the following DTCs:
DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1
DTC P0137 HO2S Circuit Low Voltage Bank 1 Sensor 2
DTC P0157 HO2S Circuit Low Voltage Bank 2 Sensor 2
When the PCM detects an HO2S signal circuit that is high, the PCM will set the following DTCs:
DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1
DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1
DTC P0138 HO2S Circuit High Voltage Bank 1 Sensor 2
DTC P0158 HO2S Circuit High Voltage Bank 2 Sensor 2
When the PCM detects no HO2S activity, the PCM will set the following DTCs:
DTC P0134 HO2S Insufficient Activity Bank 1 Sensor 1
DTC P0154 HO2S Insufficient Activity Bank 2 Sensor 1
DTC P0140 HO2S Insufficient Activity Bank 1 Sensor 2
DTC P0160 HO2S Insufficient Activity Bank 2 Sensor 2
A fault in the heated oxygen sensor heater element or its ignition feed or ground will result in an increase in time to
Closed Loop fuel control. This may cause increased emissions, especially at start-up. When the PCM detects a
malfunction in the HO2S heater circuits, the following DTCs will set:
DTC P0135 Heater Circuit Bank 1 Sensor 1
DTC P0155 Heater Circuit Bank 2 Sensor 1
DTC P0141 Heater Circuit Bank 1 Sensor 2
DTC P0161 Heater Circuit Bank 2 Sensor 2
The PCM also has the ability to detect the following HO2S problems:
HO2S response
Switching
Transition time
Incorrect ratio voltage
The PCM stores a DTC that indicates degraded HO2S performance if any of the above is detected.
Rear Heated Oxygen Sensors (HO2S)
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way
catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC an
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CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also redu
NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the Bank 1 HO2S 2 and the B
2 HO2S 2 heated oxygen sensors. The front HO2S sensors produces an output signal which indicates the amount ofoxygen present in the exhaust gas entering the three-way catalytic converter. The rear HO2S sensors produces an out
signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalysts ability to conver
exhaust gases efficiently. If the catalyst is operating efficiently, the front sensors will produce a far more active signathan that produced by the rear sensors.
The catalyst monitor sensors operate the same as the fuel control sensors. Although the Bank 1 HO2S 2 and Bank 2
HO2S 2 sensors main function is catalyst monitoring, they also play a limited role in fuel control. If a sensor output
indicates a voltage either above or below the 450 millivolt bias voltage for an extended period of time, the PCM willmake a slight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring
Throttle Position (TP) Sensor
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(1) Powertrain Control Module (PCM)
(2) Throttle Position (TP) Sensor
(3) Throttle Valve
The Throttle Position (TP) sensor is a potentiometer. The TP sensor is connected to the throttle shaft on the throttlebody. By monitoring the voltage on the signal line, the PCM calculates throttle position. As the throttle valve angle
changed (accelerator pedal moved), the TP sensor signal also changes. At a closed throttle position, the output of the
sensor is low. As the throttle valve opens, the output increases so that at Wide Open Throttle (WOT), the output voltshould be above 4.0 volts.
The PCM calculates fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor may
cause intermittent bursts of fuel from an injector. This may cause an unstable idle because the PCM detects the thrott
is moving.
When the PCM detects a malfunction with the TP sensor circuits, the following DTCs will set:
DTC P0121 circuit performance malfunction.
DTC P0122 circuit low.
DTC P0123 circuit high.
DTC P1121 intermittent circuit high. DTC P1122 intermittent circuit low.
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EVAP Purge Vacuum Switch
The EVAP Purge Vacuum Switch is used by the PCM to monitor EVAP canister purge solenoid operation and purgesystem integrity. The EVAP Purge Vacuum Switch should be closed to ground with no vacuum present (0% EVAP
Purge PWM). With EVAP Purge PWM at 25% or greater, the EVAP Purge Vacuum Switch should open.
An incorrect EVAP Purge system flow should set a DTC P0441. A continuous purge condition with no purge
commanded by the PCM should set a DTC P1441. Refer to Evaporative Emission (EVAP) Control System for acomplete description of the EVAP system.
Knock Sensors (KS)
The Knock Sensor (KS) system is used to detect engine detonation. The PCM will retard the spark timing based on t
signals from the KS module. The Knock Sensor(s) produce an AC voltage that is sent to the KS module. The amoun
AC voltage produced is proportional to the amount of knock.
An operating engine produces a normal amount of engine mechanical vibration (Noise). The knock sensor(s) willproduce an AC voltage signal from this Noise. When an engine is operating, the PCM will learn the minimum and
maximum frequency of the noise the engine produces. When the PCM determines that this frequency is less than or
greater than the expected amount, a knock sensor DTC will set.
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A/C Request Signal
The A/C request circuit signals the PCM when an A/C mode is selected at the A/C control head. The PCM uses this
information enable the A/C compressor clutch and to adjust the idle speed before turning ON the A/C clutch. If thissignal is not available to the PCM, the A/C compressor will be inoperative.
Park/Neutral Position (PNP) Switch (Automatic Transmission) The PNP switch indicates to the PCM when the
transmission is in park, neutral, or drive. This information is used for the EGR and IAC valve operation.
Refer to Electrical Diagnosis for more information on the PNP switch. The PNP switch is part of theneutral/start and backup light switch assembly. Refer to Park/Neutral Position Switch diagnosis.
Important: Vehicle should not be driven with the PNP switch disconnected, as idle quality will be affected.
Having the switch disconnected may also cause a VSS DTC to set.
Vehicle Speed Sensor (VSS)
The Vehicle Speed Sensor (VSS) is a pulse counter type input that informs the PCM how fast the vehicle is being
driven. The VSS system uses an inductive sensor mounted in the tail housing of the transmission and a toothed reluc
wheel on the tail shaft. As the reluctor rotates, the teeth alternately interfere with the magnetic field of the sensorcreating an induced voltage pulse.
The VSS produces an AC voltage signal that increases with vehicle speed. The PCM processes this signal and sends
to the following components:
Instrument Panel.
Radio control head.
Chime Module.
Cruise Control Module.
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Vehicle Speed Signal (VSS) Buffer Module
The VSS buffer module (1) is an electronic device. The VSS buffer module process inputs from the vehicle speedsensor and outputs various signals. The VSS buffer module outputs a 4000 pulse per mile signal. This signal is used
the PCM to determine vehicle speed. The PCM uses vehicle speed signal input for cruise control and fuel cutoff. The
VSS buffer module is matched to the vehicle based on transmission, final drive ratio and tire size. The VSS buffermodule is located behind the instrument panel. Note: This is for 85-95 cars and trucks
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Crankshaft Position Sensor (CKP)
The crankshaft position sensor provides the PCM with crankshaft speed and crankshaft position. The PCM utilizes th
information to determine if an engine Misfire is present. The PCM monitors the CKP sensor for momentarily drop in
crankshaft speed to determine if a misfire is occurring. When the PCM detects a misfire, a DTC P0300 will set.
The PCM also monitors the CKP sensor signal circuit for malfunctions. The PCM monitors CKP signal and the Highand Low resolution signals. The PCM calculates these signals to determine a ratio. When the PCM detects that the ra
is out of normal operating range, the PCM will set a DTC P0335 or a DTC P0336.
Camshaft Position (CMP) Sensor
The Camshaft Position (CMP) sensor is located within the distributor. The operation of the CMP sensor is very simito the Crankshaft Position (CKP) sensor. The CMP sensor will provide one pulse per camshaft revolution (1x signal
This signal will not affect the driveability of the vehicle. The VCM utilizes this signal in conjunction with the
crankshaft position in order to determine which cylinder(s) are misfiring. Note: This is for 96-02 cars and trucks
Enhanced Ignition System General Description
The Enhanced Ignition system used on all of the OBD II engines somewhat resembles the current Distributor Ignitio
(DI) system described in the Ignition Systems. However, the system has been greatly enhanced in order to becompatible with the new OBD II regulations. The Enhanced Ignition system provides a spark at precisely the correcttime in order to ignite the air and the fuel mixture for optimum performance and fuel economy. The system consists
the following components:
The VCM
The Distributor
The Ignition Coil Driver Module
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The Ignition Coil
The Crankshaft Position Sensor
This system does not use the ignition module used on the DI systems in the past. The VCM controller now controls tIgnition Control (IC) and Bypass functions.
The crankshaft sensor, located in the front engine cover, is perpendicular to a target wheel attached to the crankshaft
The target wheel is equipped with slots situated 60 apart. As the crankshaft rotates, the target wheel rotates past the
crankshaft position sensor. The rising and falling edges created by the slots cause a signal to be sent back to the VCMThis signal occurs three times per crankshaft revolution and is referred to the 3x signal.
The VCM then utilizes this 3x signal in order to provide the correct spark to the engine by way of the single coil driv
module. The single coil driver module is basically an electronic switch that when commanded by the VCM, causes th
primary coil voltage to breakdown, energizing the secondary coil and providing a spark via the coil wire to theDistributor cap. The Distributor consists of the following components:
1. The Cap and Rotor2. The Camshaft Position Sensor
3. The gear drive and shaft
The camshaft drives the Distributor shaft which rotates, providing a spark to the correct cylinder by way of the cap a
rotor. The camshaft position sensor functions much like the crankshaft sensor previously described but provides only
1x signal to the VCM. That is, for every 2 rotations of the crankshaft, there is 1 rotation of the camshaft. Note that th
camshaft position sensor will not affect the driveability. The sole purpose of the camshaft position sensor is to providthe VCM with the necessary information for the misfire DTCs.
Ignition Control (IC)
The vehicle control module (VCM) software controls all of the ignition control (IC) and bypass functions. This redu
the number of circuits outside of the controller and ultimately reduces the possibility for shorts or opens inthose circuits that could result in driveability complaints or diagnostic trouble codes (DTCs).
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The Crankshaft Position Sensor (CKP Sensor) is located in the front engine cover and is perpendicular to the cranksh
target wheel. The air gap between the sensor and the wheel is preset and not adjustable. The target wheel has three sl60 apart and is keyed to the crankshaft. As the target wheel rotates, the slots passing by the sensor create a change in
the magnetic field of the sensor which results in an induced voltage pulse. One revolution of the crankshaft results in
three pulses (3x signal). Based on these pulses, the VCM is able to determine crankshaft position and the engine speThe VCM then activates the fuel injector and provides a spark to the Distributor. The relationship between the
crankshaft position sensor and the target wheel is crucial. The sensor must be exactly perpendicular to the target whe
with the correct air gap.
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The Distributor is actually an assembly that contains the Camshaft Position (CKP Sensor), the cap, the rotor and the
shaft. The Distributor is splined by a helical gear to the camshaft and rotates providing a spark to each spark plug wiWhen servicing the Distributor, it is critical to ensure proper cap sealing to the Distributor body and correct installati
to the camshaft. If the Distributor is installed a tooth off in relation to the camshaft, a DTC sets. The Distributor is no
repairable and must be replaced as an assembly.
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The Camshaft Position (CMP) sensor is located within the Distributor. The operation of the CMP is very similar to tCrankshaft Position (CKP Sensor) however, the CMP provides one pulse per camshaft revolution (1x signal). This
signal is not detrimental to the driveability of the vehicle. The VCM utilizes this signal in conjunction with the
crankshaft position to determine which cylinders are misfiring.
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The Ignition Coil Driver Module (3, 4 - ICM Bolt) is mounted on a bracket (5, 6, 1-Bracket Attachment Rivet) next
the coil. The VCM signals the ICD to turn ON the primary current to the ignition coil (2) by pulling the IC line high
volts). The ICD turns the primary current ON and OFF by applying and removing the ground to the primary windingthe appropriate time. This module is of minimum function. The module does not contain backup calibrations that allo
the engine to continue to run if the IC signal is lost.
Distributor Ignition System for LT1
The distributor ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixtuat the correct time. To provide improved engine performance, fuel economy, and control of exhaust emissions, the P
controls distributor spark advance (timing) with an Ignition Control (IC) system. Only the IC system will be describe
here. Additional information on the system is found in Ignition System (6D).
To properly control ignition/combustion timing the PCM needs to know:
Camshaft position.
Engine speed (RPM). Engine load (manifold pressure or vacuum).
Atmospheric (barometric) pressure.
Engine coolant temperature.
The amount of detonation.
(1) Ignition Coil Wire
(2) Distributor
(3) Ignition Coil
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(4) Ignition Coil Module
The distributor ignition system is a net build distributor (no timing adjustment) that provides angle based timing
information to the PCM for individual cylinder spark timing. The ignition module is capable of providing both 4X an180X timing pulses each crankshaft revolution. Using these timing pulses, the PCM processes ignition spark timing
sends an IC signal to the ignition coil module to activate the secondary ignition system.
The PCM provides the distributor with the following:
Ignition voltage circuit.
Ground circuit.
Two 5 volt reference voltages to the ignition control module.
As the camshaft turns (during crank or run), a slotted two-track timing disk is rotated inside the ignition control mod
Each time a slot in either track of the disk is properly aligned, the ignition control module will pulse one of the 5 vol
reference voltages to ground. A reference signal is generated each time the PCM detects that the reference voltages h
been grounded by the ignition control module. When the PCM detects reference signals, ignition timing can beprocessed.
The PCM will also compare the 4X and the 180X signals to each other to determine the location of the number one
cylinder and top dead center. In addition, if only one signal is being received by the PCM a Diagnostic Trouble Code(DTC) will be set. DTC P1371 will be set if the 4X signal is missing and DTC P0372 will be set if the 180X signal is
missing. The vehicle will not run if the 4X (Reference) signal is not available at the PCM for processing.
The Ignition Control (IC) system consists of the following:
Camshaft Position Sensor
Ignition Coil Ignition Coil Module
Powertrain Control Module.
These circuits perform the following functions:
Low resolution signal reference.
o This provides the PCM with reference signals, firing order, and camshaft position information. If the
resolution signal circuit becomes open or grounded, the engine will not run because the PCM will not
operate the ignition coil module, fuel pump, or the fuel injectors.o A DTC P1371 will set if the PCM receives high resolution signal references without the low resolutio
signals.
High resolution signal reference.
o This provides the PCM with detailed reference signals and crankshaft position information.
o If this circuit becomes opens or grounded a DTC P0372 will set and the engine will still run.
o When there is a malfunction with the high resolution circuit, excessive crank times will be experience
System ground.
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o This circuit is grounded at the PCM and provides ground for the distributor to generate low and high
resolution signal reference signals.
o If this circuit becomes open, the engine will not run since there will be no reference information.
Ignition Control (IC).
o This circuit controls the ignition coil ON and OFF time. It signals the ignition coil module to beginprimary coil dwell current when the IC is high. The ignition coil module shuts OFF ignition coil currwhen the signal goes low.
o If this circuit becomes open, shorted to voltage, or grounded, the engine will not start and a DTC P13
or P1361 will set.
Results of Incorrect Operation
An open IC circuit will set a DTC P1351. A grounded IC circuit will set a DTC P1361. An open or grounded IC circ
will result in an engine cranks but will not run. An open or ground in the low resolution signal circuit will set a DTC
P1371 and the engine will not start. If the high resolution signal circuit becomes open or grounded a DTC P0372 wo
set. This will cause reduced performance and poor fuel economy.
An inoperative distributor vent system may cause premature distributor failure. To check system operation perform
Distributor Vent System Check .
The PCM uses information from the MAP and engine coolant temperature sensor in addition to RPM to calculate sp
advance as follows:
Cold engine = More spark advance.
Engine under minimum load based on RPM and low amount of air flow - More spark advance.
Hot engine = Less spark advance.
Engine under heavy load based on RPM and high amount of air flow - Less spark advance.
For removal and replacement of ignition system components, refer to Section 6D4, Ignition System.
The description, operation and repair procedures of the distributor ignition system components are found in Service
Category Ignition Systems. For misfire or ignition control check, refer to the following DTCs:
P0300
P0323
P0372
P1351
P1361 P1371
Electronic Ignition (EI) System Description (LS1/LS6 and LS truck)
Ignition System Overview
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The electronic ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixtu
at the correct time. To provide optimum engine performance, fuel economy, and control of exhaust emissions, the PC
controls the spark advance of the ignition system. The Electronic ignition system has the following advantages over mechanical distributor system:
No moving parts. Less maintenance.
Remote mounting capability. No mechanical load on the engine.
More coil cool down time between firing events.
Elimination of mechanical timing adjustments.
Increased available ignition coil saturation time.
The electronic ignition system does not use the conventional distributor and coil. The ignition system consists of the
following components/circuits:
Eight ignition coils/modules Eight Ignition Control (IC) circuits
Camshaft Position (CMP) sensor
1X Camshaft reluctor wheel
Crankshaft Position (CKP) sensor 24X Crankshaft reluctor wheel
Related connecting wires
Powertrain Control Module (PCM)
Crankshaft Position Sensor and Reluctor Wheel
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The Crankshaft Position (CKP) sensor is located in the right rear of the engine, behind the starter. The CKP sensor isdual magneto resistive type sensor. This sensor is not speed dependent. The dual micro switches monitor both notche
of the reluctor wheel for greater accuracy. The CKP sensor works in conjunction with a 24X reluctor wheel. The
reluctor wheel is mounted on the rear of the crankshaft. The 24X reluctor wheel uses two different width notches tha
are 15 degrees apart. This Pulse Width Encoded pattern allows cylinder position identification within 90 degrees ofcrankshaft rotation. In some cases, cylinder identification can be located in 45 degrees of crankshaft rotation. This
reluctor wheel also has dual track notches that are 180 degrees out of phase. The dual track design allows for quicker
starts and accuracy.
The PCM also receives a 4X signal from the Crankshaft Position sensor. The PCM utilizes the 4X signal for the
following:
Misfire
Tachometer output
Spark control
Fuel control
Certain diagnostics
Observe that as long as the PCM receives the Crankshaft Position sensor 24X signal, the engine will start. The PCM
determine top dead center for all cylinders by using the Crankshaft Position sensor 24X signal alone. The CamshaftPosition sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke, o
the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engstarted. If the PCM does not detect an increase in engine speed, the PCM assumes it incorrectly synchronized to the
exhaust stroke and re-synchronizes to the opposite cam position. A slightly longer cranking time may be a symptom
this condition.
Camshaft Position Sensor
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The ignition system on this vehicle features a multiple coil ignition and is known as coil near plug. The secondary
ignition wires are short compared with a distributor ignition system wire. Eight ignition coils/modules are individual
mounted above each cylinder on the rocker covers. The coils/modules are fired sequentially. There is an Ignition
Control (IC) circuit for each ignition coil/module. The eight ignition control circuits are connected to the PCM. All
ignition timing decisions are made by the PCM, which triggers each coil/module individually. The ignition coil/modare supplied with the following circuits:
Ignition feed circuit
Ignition control circuit
Ground circuit
Reference low circuit
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The ignition feed circuits are fused separately for each bank of the engine. The two fuses also supply power to theinjectors for that bank of the engine. Each coil/module is serviced separately.
This system puts out very high ignition energy for plug firing. The ignition wires are shorter so less energy is lost to
ignition wire resistance. Also, since the firing is sequential, each coil has seven ignition events to saturate as opposed
the three in a waste spark arrangement. Futhermore, no energy is lost to the resistance of a waste spark system.
Circuits Affecting Ignition Control
To properly control ignition timing, the PCM relies on the following information:
Engine load (manifold pressure or vacuum)
Atmospheric (barometric) pressure
Engine temperature
Intake air temperature
Crankshaft position
Engine speed (RPM)
The Ignition Control (IC) system consists of the following components:
Ignition coil/modules
24X crankshaft position sensor
Powertrain Control Module (PCM)
All connecting wires
The Ignition Control utilizes the following to control spark timing functions:
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24X signal - The 24X crankshaft position sensor sends a signal to the PCM. The PCM uses this signal to
determine crankshaft position. The PCM also utilizes this signal to trigger the fuel injectors.
Ignition Control (IC) circuits - The PCM uses these circuits to trigger the ignition coil/modules. The PCM usthe crankshaft reference signal to calculate the amount of spark advance needed.
Ignition Information
There are important considerations to point out when servicing the ignition system. The following Noteworthy
Information will list some of these to help the technician in servicing the ignition system.
The ignition coils secondary voltage output capabilities are very high - more than 40,000 volts. Avoid body
contact with secondary high voltage ignition components when the engine is running, or personal injury may
result!
The 24X crankshaft position sensor is the most critical part of the ignition system. If the sensor is damaged sthat pulses are not generated, the engine will not start!
Crankshaft position sensor clearance is very important! The sensor must not contact the rotating interrupter r
at any time, or sensor damage will result. If the interrupter ring is bent, the interrupter ring blades will destrothe sensor.
Ignition timing is not adjustable. There are no timing marks on the crankshaft balancer or timing chain cover
Be careful not to damage the secondary ignition wires or boots when servicing the ignition system. Rotate eaboot to dislodge it from the plug or coil tower before pulling it from either a spark plug or the ignition coil.
Never pierce a secondary ignition wire or boot for any testing purposes! Future problems are guaranteed if
pinpoints or test lights are pushed through the insulation for testing.
Powertrain Control Module (PCM)
The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. To provideoptimum driveability and emissions, the PCM monitors input signals from the following components to calculate
Ignition Control (IC) spark timing:
The Engine Coolant Temperature (ECT) sensor
The Intake Air Temperature (IAT) sensor
The Mass Air Flow (MAF) sensor
The Knock Sensor
The Trans Range inputs from Transaxle Range switch
The Throttle Position (TP) sensor
The Vehicle Speed Sensor (VSS)
Results of Incorrect Operation
An Ignition control circuit that is open, grounded, or shorted to voltage will set an ignition control circuit DTC. If afault occurs in the IC output circuit when the engine is running, the engine will experience a misfire. DTCs P0351-
P0358 will set when a malfunction is detected with an Ignition Control circuit. When an Ignition control DTC sets, t
PCM disables the injector for the appropriate cylinder.
The PCM uses information from the engine coolant temperature sensor in addition to RPM to calculate spark advancvalues as follows:
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High RPM = more advance
Cold engine = more advance
Low RPM = less advance
Hot engine = less advance
Therefore, detonation could be caused by high resistance in the engine coolant temperature sensor circuit. Poorperformance could be caused by low resistance in the engine coolant temperature sensor circuit.
If the engine cranks but will not run or immediately stalls, the Engine Cranks But Will Not Run diagnostic table musused to determine if the failure is in the ignition system or the fuel system. If DTC P0300, P0341, P0342, P0343, P0
P0336 is set, the appropriate diagnostic trouble code table must be used for diagnosis.
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