ASE G1 Auto Maintenance and Light RepairElectrical/Electronic SystemsHard
A technician is diagnosing a vehicle with a 'CHECK ENGINE' light illuminated. They connect a scan tool and retrieve a diagnostic trouble code (DTC) P0301, indicating a misfire on cylinder 1. What is the NEXT logical step in diagnosing this issue?
- AClear the DTC and test drive the vehicle.
- BReplace the spark plug for cylinder 1.
- CCheck for technical service bulletins (TSBs) related to P0301.
- DPerform a compression test on cylinder 1.
Show answer & explanationAnswer & explanation
Correct answer: C. Check for technical service bulletins (TSBs) related to P0301.
While replacing the spark plug or performing a compression test might be part of the diagnostic process, the most logical and efficient 'next step' after retrieving a specific DTC is to consult service information, including TSBs. TSBs often provide known fixes, updated diagnostic procedures, or specific component recommendations for common issues associated with certain DTCs, saving diagnostic time and ensuring the latest repair strategy is used.
Why the other options are wrong
- A. Clearing the DTC without addressing the underlying cause is not a diagnostic step; it only temporarily turns off the light and the problem will likely return.
- B. Replacing the spark plug is a common step, but without further diagnosis, it's just guessing. The misfire could be due to ignition coil, injector, or compression issues.
- D. A compression test is a valid diagnostic step for misfires, but it's typically performed after checking basic ignition/fuel components or after consulting service information to narrow down the possibilities. TSBs can often guide whether to go straight to a compression test or check other items first.
DTC Diagnostic Procedure
A systematic approach to diagnosing diagnostic trouble codes (DTCs) to efficiently identify and repair the root cause.
- Always start with retrieving and documenting DTCs and freeze frame data.
- Consulting service information (manuals, TSBs) is a critical early step.
- Avoid replacing parts based solely on a DTC without further testing.
Memory trick: Code in hand, info expand, then test the land.