Automotive Diagnostics Using The Controller Area Network (CAN)

Denise R. James

Topics Covered

• Overview of CAN

• Layout in Vehicle

• OBD II

• Little Known Car Bonuses

• Android App Obtaining OBD II Codes

Overview of CAN

• Serial Data Bus used to transmit and receive messages between electronic control modules.

• High Speed CAN Data is 250 mps or 500 mps. Medium Speed CAN Data is 125 mps.

• SAE-J1939 is a subset of the CAN 2.0B. It is used for diesel engines.

CAN 2.0B 11-bit Protocol

• Initially CAN used 11-bit protocols until around 1991.

• 11 bits wide, 211, 2048 different message types are possible.

CAN 2.0B 29-bit Protocols

• 29 bits wide, 229, 536870912 different message types are possible.

CAN 2.0B 11-bit and 29-bit Protocols

• If a Remote and Data Frame have the same identifier, the Data Frame wins the arbitration. This is what the Remote Frame is requesting.

• Data frames have higher priority over Remote Frames. Identifiers determine priority.

• The node with the lowest ID will always win the arbitration, and therefore has the highest priority.

CAN Nodes Shown With Terminating Resistors

CAN_H

CAN_L

120 120

CAN Buses In Vehicle

Example of High Speed CAN Bus – 500 mps

DPFE Sensor

Injector Solenoid

Microprocessor

CAN 1 controller

Powertrain Control Unit

CAN Transceiver

CAN_L

CAN_H

Tx Rx

120 Ω

Sensor Actuator

Microprocessor

CAN controller

Adaptive Cruise Control Unit

CAN Transceiver

CAN_L

CAN_H

Tx Rx

120 Ω

May have 20 units

CAN 2 controller

Terminating Resistors Reside in Units

~1995 Ford Ranger Powertrain Control Unit

Example of Low Speed CAN Bus – 125 mps

DPFE Sensor

Transmission Solenoid

Microprocessor

CAN 1 controller

Powertrain Control Unit

CAN Transceiver

CAN_L

CAN_H

Tx Rx

120 Ω

Sensor Actuator

Microprocessor

CAN controller

Adaptive Cruise Control Unit

CAN Transceiver

CAN_L

CAN_H

Tx Rx

120 Ω

May have 20 units

CAN 2 controller

Terminating Resistors Reside in Units

Example of LIN, Local Interconnect Network Bus – 1 kbit/s to 20 kbit/s

• Cost effective one wire serial bus with a much lower speed than CAN bus.

• Used for non-vital automotive functions such as seat controls and steering wheel controls

• LIN is preferred over CAN when speed or bandwidth are not important.

• No license required to implement LIN.

• Not part of OBD.

On Board Diagnostics - OBD II

• In 1996 the government mandated On Board Diagnostics for emissions control. As of 2008, the government standard is now one serial data bus, ISO 15765-4. This hardware on the Diagnostics Terminal Connector, and the software message protocol is compatible with CAN 2.0

• 2008: All cars sold in the United States are

required to use the ISO 15765-4 signaling standard (a subset of the Controller Area Network (CAN) bus).

Diagnostic Terminal Connector - DTC

12 V Female DTC as in a vehicle

24 V Female DTC as in a vehicle

Will talk about 12 V DTC in this presentation

Assure a 24 v mating connector will not connect to a 12 v connector

Vehicle Diagnostic Terminal Connector

• The Female OBD-II Connector is found on the driver's side under the instrument panel. It must be within 2 feet of the steering wheel. SAE J1962 defines two connectors, one for 12 volt cars and one for 24 volt cars. The different middle groove assures a 12 volt connector only connects to a mating 12 volt male connector and a 24 volt connector connects with another 24 volt connector.

12 V Female Diagnostic Connector in Vehicle 1 Manufacturer discretion 9 Manufacturer discretion

2 Manufacturer discretion 10 Manufacturer discretion

3 Manufacturer discretion 11 Manufacturer discretion

4 Chassis ground 12 Manufacturer discretion

5 Signal ground 13 Manufacturer discretion

6 CAN-High (ISO 15765-4 ) 14 CAN-Low (ISO 15765-4)

7 Manufacturer discretion 15 Manufacturer discretion

8 Manufacturer discretion 16 Ignition Battery

Ignition battery instead of battery to assure the battery is not drained due to CAN activity. CAN is inactive until it is provided Ignition Battery.

For Model Year 2008+ OBD II CAN Pin Out

For Cars 2008 and beyond are required to have CAN 2.0 message protocol with CAN-High (ISO 15765-4 ) on Pin 6, CAN-Low (ISO 15765-4 ) on Pin 14.

Diagnostic Terminal Connector As Shown In The Vehicle Used To Retrieve OBD-II Codes

Pin 6

Pin 14

Required pins, 4, 5, 6, 14, and 15 are populated. In this case pin 11 is also populated

On Board Diagnostics Monitoring

• CARB has OBD II requirements for gasoline engine and diesel engines in vehicles under 6,350 kg (14,000 lb) gross vehicle weight rating (GVWR).

• The engine manufacturer diagnostics (EMD) system is used on vehicles over 6,350 kg (14,000 lb) GVWR. SAE-J1939, a subset of signaling standard CAN.

On Board Diagnostics Monitoring

Government requirements state that the “Service Engine Soon” and “Check Engine” Malfunction Indicator Lights illuminate when certain emission levels occur. On vehicles equipped with OBD-II, the light has two stages: steady (indicating a minor fault such as a loose gas cap or failing oxygen sensor) and flashing (indicating a severe fault, that could potentially damage the catalytic converter if left uncorrected for an extended period).

Don’t Drive until Serviced

Is the Fuel Cover Open?

Volkswagen Diesel OBD II Issues

From: New York Times Article “How Volkswagen Got Away With Diesel Deception”

Turning off emissions during normal operation gives better gas mileage

Little Known Car Bonuses

• Obtaining New Parts After Warranty Expires

An automotive part that has failed after sale is of high interest to product engineers. I have never heard of an automotive manufacturer not paying for a failed component in order to receive the part for failure analysis. A failed component is a gold mine of potential quality improvements. The customer has actually done the testing in the field for the Engineer. This works when the dealer repair shop name is the same as the manufacturer dealer. A Nissan dealer will most likely call Nissan Automotive and ask if they would like to pay for the replacement part in lieu of the failed part.

Little Known Car Bonuses

• Up To Date Software Revisions Installed

Whenever your car is in for service, oil change, brakes, etc at the dealer, ask if they will install the latest software updates for your vehicle. There are software updates that are nor recalls but are nice to have. They are intended for when the car is brought in for the issue the software was designed for. Do not wait to see if you will have the issue. Get the free latest software update.

Little Known Car Bonuses

• Vector CAN Posters, App. Notes

The posters displayed are all free from Vector, a well known automotive serial data bus support supplier. www.vector.com

Android App Obtaining OBD II Codes

• Use an OBD Diagnostic Hardware Interface. I purchased mine on Amazon for about $12

• OBD II application. I choose the Torque OBD II Android app to work with my Nexus 7 tablet. Most cell phones are acceptable. Purchase the app that matches your phone Apple or Android.

Android App Obtaining OBD II Codes • This is what an Diagnostic Terminal Connector looks like in a Camry. Pins 4, 5, 6,

14, 15 are populated as required. Pins 7, 14, and 16 are also populated.

Android App Obtaining OBD II Codes • Plug in the OBD Diagnostic Interface to the Diagnostic Terminal Connector

in the Car

Red Light Turns On with Ignition On

Android App Obtaining OBD II Codes • Pair the OBD diagnostic interface with the Nexus 7. Next select Bluetooth in

the Torque OBD app

Android App Obtaining OBD II Codes

• Add the Vehicle Camry in the App

Android App Obtaining OBD II Codes Vehicle data is displayed, OBD-11 as defined by CARB since it is the most stringent emissions requirement

OBD II Sensors Supported In Vehicle

Android App Obtaining OBD II Codes

Android App Obtaining OBD II Codes

Display with Ignition On. Zero RPM

Start The Car, get 1003 RPMs. Did not do a drive cycle

Android App Obtaining OBD II Codes

Android App Obtaining OBD II Codes Click on the Fault Icon on the main menu to search for vehicle faults. Then tap on the icon below

Searching for Faults. No faults were found in this case

Android App Obtaining OBD II Codes

References

1. California Air Resources Board, CARB. http://www.arb.ca.gov/msprog/obdprog/obdfaq.htm

2. Bosch Semiconductors http://www.bosch-

semiconductors.de/media/pdf_1/canliteratur/can2spec.pdf 3. https://en.wikipedia.org/wiki/CAN_bus#Standards 4. http://pinoutsguide.com/CarElectronics/car_obd2_pinout.shtml 5. http://openxcplatform.com/ 6. Wikipedia 7. https://www.motorcraftservice.com/pubs/content/~WV8E/~MUS

~LEN/14/V8E1013.HTM 8. Philips Semiconductors Application Note HAI/AN 92 002