Strategy Based
Diagnostics
Seven-step systematic approach to
diagnosing automotive systems
Strategy Based Diagnostics
In any scenario, when you are given a work order and the keys to
the vehicle, what are your first two steps?
1. Verify the customer’s
concern
2. Preliminary checks
(i.e. visual
confirmation, service
history, unusual
sounds, etc.)
Strategy Based Diagnostics
1. VERIFY CUSTOMER CONCERN
•Duplicating the concern is an important
starting point.
•The service writer should collect as
much information from the customer as
possible.
•When does the problem occur?
•Under what conditions?
•How often does it occur?
Strategy Based Diagnostics
2. Preliminary Checks
•Do a visual inspection
•Look for loose or corroded connections,
blown fuses, unusual noises, smells,
vibrations or movements
•Look for aftermarket accessories
•Check vehicle history
Strategy Based Diagnostics
3. DIAGNOSTIC SYSTEM CHECKS
•Get the codes.
•Even with a no-start condition, there may be
DTCs for the theft deterrent, ignition and fuel
systems.
•Be aware that if you fix one DTC, another DTC may set
because now other enable criteria can be met.
•
Strategy Based Diagnostics
3. DIAGNOSTIC SYSTEM CHECKS
•Follow the order for troubleshooting
multiple DTCs recommended in service
information.
Strategy Based Diagnostics
3. DIAGNOSTIC SYSTEM CHECKS
•Finally, do not erase DTCs to see if they
reset.
•The DTCs may not reset in your repair stall,
but they may reset for the customer down
the road.
Strategy Based Diagnostics
4. CHECK FOR TECHNICAL SERVICE BULLETINS (TSBs)
•There may be PCM programming updates, part
changes and wiring concerns. Always follow the
latest information.
Strategy Based Diagnostics
5.1 STORED DTCS
•If there is a stored DTC, follow the related diagnostic
chart.
•The results of viewing data may also lead you into
another diagnostic chart.
Strategy Based Diagnostics
5.2 SYMPTOMS WITHOUT DTCs
•In some instances, you may need to follow a
symptom table, although it is rare with OBD-II.
Strategy Based Diagnostics
5.3 NO PUBLISHED DIAGNOSTICS
•Do not forget the basics.
•Such faults as poor grounds and low voltage can
lead to driveability concerns.
•The PCM management always assumes the engine is
breathing correctly, the fuel pump is healthy and
ignition is occurring at the correct time with the
correct voltage.
Strategy Based Diagnostics
5.4 INTERMITTENT
•Freeze frame and fail records can help with intermittent
faults. If the DTC sets, freeze frame and fail records are
also stored.
•Items normally asked of a customer, such as temperature,
load, speed and mileage between the first and last failure,
can now be viewed in freeze frame and fail record data.
Strategy Based Diagnostics
5.5 OPERATING AS DESIGNED
•You may have to educate customers about things
that cause a code to set.
•Example – refueling your car with it running may
set an EVAP code.
•Example – low tire pressure may set an ABS
code.
Strategy Based Diagnostics
6. ISOLATE ROOT CAUSE/RE-EXAMINE CONCERN
•Based on the diagnostics performed, determine
proper repair.
•If you cannot isolate the cause of the problem return
to step one and continue.
•It may be necessary to call technical support.
Strategy Based Diagnostics
7. REPAIR & VERIFY THE REPAIR
•The ultimate method of verifying a repair is to
perform a drive cycle (see next slide).
•This runs all monitors and will test all emissionrelated on-board diagnostics. When all diagnostics
have run, the system status (Inspection/Maintenance
ready) "flags“ are set to YES.
•If you do not run any monitors, let the customer
know that he/she will be performing the drive cycle
as the vehicle is operated.
Strategy Based Diagnostics