Transcript Sherlock Holmes Diagnosis

Sherlock Holmes Diagnosis
NACAT
July, 2010
Jim Morton
Jim Halderman
Introductions
• Jim Morton-(aka
Sherlock Holmes)
• Jim Halderman-(aka
Mr. Watson)
Topics to be Discussed
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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:
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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 Study
Chrysler 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
• [email protected]
• Jim Halderman
[email protected]