ASE A1 Engine RepairEngine Electrical Systems (General)Hard
A technician is diagnosing a 'no-start' condition on a vehicle where the engine cranks normally but does not fire. Diagnostic Trouble Codes (DTCs) P0201 (Injector Circuit/Open - Cylinder 1) and P0351 (Ignition Coil 'A' Primary/Secondary Circuit Malfunction) are present. Which of the following is the MOST appropriate next diagnostic step?
- APerform a compression test on cylinder 1.
- BCheck the power supply and ground to the Powertrain Control Module (PCM).
- CInspect the crankshaft position (CKP) sensor signal.
- DReplace the fuel pump and retest.
Show answer & explanationAnswer & explanation
Correct answer: B. Check the power supply and ground to the Powertrain Control Module (PCM).
Given multiple circuit malfunction codes (P0201 for injector, P0351 for ignition coil) affecting different systems, a common denominator like a shared power supply or ground to the PCM (which controls both) is the most logical place to start. If the PCM isn't receiving proper power or ground, it cannot effectively control these circuits.
Why the other options are wrong
- A. A compression test would diagnose a mechanical issue, not an electrical circuit malfunction indicated by these DTCs. It's not relevant at this stage.
- C. While a CKP sensor signal is crucial for starting, these specific DTCs point to injector and ignition coil circuit issues, not a lack of CKP signal itself. If the CKP was bad, you'd likely see a P0335 code.
- D. Replacing the fuel pump would address fuel delivery, but not the specific electrical circuit faults indicated for both injector and ignition coil, which are controlled by the PCM.
Multiple Circuit DTCs
When multiple Diagnostic Trouble Codes (DTCs) appear for various circuits controlled by a single module (e.g., PCM), the root cause might be a common element like the module's power, ground, or internal fault.
- Look for common denominators when multiple codes exist.
- PCM power/ground is a critical common point.
- Avoid replacing individual components without deeper diagnosis.
Memory trick: Multiple codes? Find the 'Common Thread' before you get threaded!