A technician is diagnosing a vehicle that exhibits a sudden loss of engine power, accompanied by a 'check engine' light and a P0203 DTC (Injector Circuit / Open - Cylinder 3). After inspecting the wiring harness and connectors for Cylinder 3 injector and finding no obvious damage, what is the next logical step in diagnosis?
- ACheck fuel pressure at the fuel rail.
- BReplace the engine control module (ECM).
- CPerform a compression test on Cylinder 3.
- DSwap the Cylinder 3 injector with a known good injector from another cylinder.
Show answer & explanationAnswer & explanation
Correct answer: D. Swap the Cylinder 3 injector with a known good injector from another cylinder.
A P0203 indicates an open circuit in the fuel injector circuit for Cylinder 3. Since the wiring harness was inspected, the next logical step is to determine if the fault lies with the injector itself or the engine control module (ECM) driver. Swapping the injector allows you to see if the fault follows the injector (indicating a faulty injector) or remains on Cylinder 3 (indicating an ECM driver issue or a wiring fault not yet found).
Why the other options are wrong
- A. Checking fuel pressure is for fuel delivery issues, not an electrical injector circuit fault.
- B. Replacing the ECM is a last resort after thoroughly ruling out all other components in the circuit. It's premature at this stage.
- C. A compression test is for mechanical issues, not an electrical injector circuit fault implied by P0203.
Injector Circuit Fault Diagnosis
For an injector circuit open DTC (P020x), after checking wiring, the next step is typically to swap the suspected injector with another to determine if the fault lies with the injector itself or the control circuit (wiring/ECM driver).
- P020x = injector circuit fault.
- Check wiring first.
- Swap injector to isolate fault (injector vs. control).
- Test ECM driver if fault remains after swap.
Memory trick: P020x means 'Power Zero' to 'Injector'. Check 'Wire', then 'Swap'.