Seven-step systematic approach to diagnosing automotive systems

Strategy Based Diagnostics

1. Verify the customer’s concern

2. Preliminary checks (i.e. visual confirmation, service history, unusual sounds, etc.)

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?

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 emission-related 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