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Sherlock Holmes DiagnosisNACAT
July, 2010
Jim Morton
Jim Halderman
Introductions
• Jim Morton-(aka Sherlock Holmes)
• Jim Halderman-(aka Mr. Watson)
Topics to be Discussed
• Teaching the diagnostic process
• Interviewing the customer
• Interviewing the vehicle
• Interviewing the vehicle history
• The repeatable diagnostic procedure
• Tips and tricks
Teach Diagnosis?
Do you teach a diagnosis procedure?
• If so, in which course?
• All of them?
• We both teach diagnosis in all courses
• It helps make the subject “real world”
Here is What We Hear
• We get asked for help after they have tried EVERYTHING
• What we usually find is that they had no real direction or approach
• Is this happening to you too?
Isn’t this what is important?
• We all teach how to perform tests such as a compression test
• Is a compression test the first test that should be performed for a driveability problem?
• Not so much how to test, but a TRUE game plan on each driveability concern
General Tests
• Decide what GENERAL test would eliminate some of the possible causes
• In most cases we have the problem nailed after 3 general tests to the right circuit or component
Pinpoint tests
• We then decide what Pinpoint test to perform to find the root cause
The Old Days
• My father opened the hood and felt the movement or play in the cooling fan
• Sir, you need a water pump
How Does it Work Today?
• We have to go through a diagnostic procedure to determine the root cause of the concern
• Then isolate the circuit or part and perform a pinpoint test to determine the root cause
• It is easy Mr. Watson if you ask the right questions
“The” Plan
• 8 steps
• Easy to remember
• Repeated the same way each time
• Has to be continuously repeated to students otherwise they tend to forget it
Like Peeling an Onion
• Get to the heart (root cause) of the problem requires some peeling and a plan of action
Finding the “ROOT CAUSE”
• In my mobile diagnostic business, a VERY normal statement is made to me “The SAME component keeps failing”
• An example of this would be 3 electric fuel pumps in 2 years replaced on the same vehicle
First Step
• Verify the concern (sounds better than complaint?)
• If the concern can not be verified then the repair can not be verified either
• Interview the owner (driver)
The Diagnostic Interview
• Also called the Sherlock Holmes Interview
• Interview the customer
Tech Tip
• Make sure you are talking to the person that noticed the problem/concern or the person that drives the vehicle the most !
• NOT the person that happens to be the most convenient to drop the vehicle off
• Remember YOUR time is valuable also.
Is there a Problem?
• Describe the problem/concern
• Is there actual a problem?
• Does the customer know how to work all of the accessories etc.?
• Does the technician know?
Sherlock Asks
• Concern just Start?
• Last Week?
• Last Month?
• What happened or what repairs were done right before the problem started?
Interview the Vehicle
“The Milkman”
• My techs called me the “Milkman”
• They always saw me with my metal tray with a handle carrying handheld diagnostic tools
“The Milkman”
• What the “Milkman” was doing was going from vehicle to vehicle with the diagnostic interview sheet and performing basic “G” (General) tests
“The Milkman”
• Results of my “visual inspection” and “G” tests would indicate what circuits or components I felt needed “P” (pinpoint) testing
TEST DRIVE THE VEHICLE
Milk the DTCs
• A VERY good thing to look for when a DTC stores is the FREEZE FRAME
• look at what the fuel trim is, especially when there is a P0420 catalyst efficiency code
• Was the PCM trying to make a correction for fuel delivery?
Milk the DTCs
• P0420 Worksheet• 1. Check for TSBs and calibration updates
2. Check exhaust condition (leaks) 3. Verify fuel control 4. Replace the catalytic converter 5. Verify the repair
ST & LT Fuel Trim
Fuel Trim Control• The fuel trim value is a very important
diagnostic tool, if the fuel trim is very positive, like +23%, why did the PCM have to add some much extra fuel to it’s base calculation ?
“The Bends and Ends”
Checking TSBs• FORD:• 2005-2006 Crown Victoria LINCOLN:• 2005-2006 Town Car • This article supersedes TSB 06-02-8 to update the Service Procedure. • ISSUE:• Some 2005-2006 Crown Victoria police and taxi vehicles built before
December 13, 2005, and 2005-2006 Lincoln Town Car Limo vehicles may exhibit a malfunction indicator lamp (MIL) on with diagnostic trouble code (DTC) P0305, possibly accompanied with P0316, P0171, and/or P0174, especially after extended idle. This condition may be caused by fuel vaporization near injector Number 5.
Fuel Cut-Off Mode
Comparing PIDs
A bad redundant ground circuit causing the TP and MAF to go haywire
Comparing PIDs
Take notice of unstable idle due to ignition timing changing
High Authority Inputs
• The engine RPM signal comes from the CPK sensor and it must be able to calculate the engine speed very quickly
• As the number goes up, the engine is going faster
• This is usually the most important input
High Authority Inputs
• This signal is used as the basis for the fuel injector pulse signal.
MAP Relationship
Take Note that frame #9 there is only 1.7 “hg of manifold vacuum In frame # 17 there is 10.2 “hg of manifold vacuum
Narrow the problem to a system or cylinder
• This is where the “G” and “P” testing comes in
• Use a “G” (general) test to isolate the problem to a system or cylinder (or bank)
• Then use a “P” (pinpoint) test to drive down that FUNNEL in order to find the problem.
Ford Motor Co
Finding the ROOT CAUSE
• As stated in Jim Halderman’s Advance Engine Performance book
• Always ask the “5 WHYS”
• When you find the customer’s complaint, ask WHY 5 times
Finding the ROOT CAUSE• Example of this would be a P0420 code
(low catalyst efficiency)
• 1 why – because the pre & post oxygen sensors reading incorrectly
• 2 why – because air fuel ratio is too lean
• 3 why – because the fuel delivery is inadequate
• 4 why – because the fuel pump pick-up is partial clogged
• 5 why – dirt in fuel tank
Verify the Repair & Clear DTCs
• This is an important step for 2 reasons:
• 1 – YOU want to be the one to find that the repair didn’t work, not the customer.
• 2 – The are a lot of times that another DTC will not be set because there is a program that won’t allow a circuit to be monitored due to the current DTC.
• This is known as a “SUSPEND” condition
Case StudyChrysler mini van no-start
• Customer stated that it would not start unless he pounded on the dash. Finally, the vehicle wouldn’t start at all.
Step #1-Verify
Engine did not start
No spark
No Squirt
Step#2- Visual Inspection
• Yep the customer pounded on the dash
• So hard that the needles fell off
Step #3 Check DTCs
Step #4
• Checked for TSBs-nothing that was related
• Checked archives of www.iatn.net
• Bingo- found several fixes for wiring being burned near the CPK sensor
Step #5 Scan Data
• No engine RPM while cranking
Step #6- Narrow Down
Step # 6-Continued
Step #7 Root Cause
Step #8-Verify Repair
Final Thoughts
• How does the PCM put all this information together and run the engine?
• You have to think like a PCM
Summary
• We are recommending that you teach a diagnostic procedure in all courses
• Repeat, repeat and repeat the process over and over
• This way students will know what and why they are doing what test
Contact Information
• Jim Morton
• Jim Halderman
