P1240 — Injector Circuit Cylinder 7 Intermittent

Diagnostic algorithm

1. Verify DTC details: record freeze-frame data and other active/pending codes. Clear codes and attempt to re-create.
2. Visual inspection: check harness routing, connector condition, signs of heat/chafing, oil intrusion or corrosion at injector #7 and nearby harness.
3. Wiggle test: with a scan tool monitoring cylinder contribution and the injector circuit, wiggle the connector/wiring while cranking and driving to try to reproduce the code.
4. Resistance test: disconnect connector and measure injector coil resistance; compare to factory spec. Replace injector if resistance is out of spec or intermittent when gently flexed.
5. Power/ground check: backprobe the connector. Verify battery voltage at the feed circuit and that the PCM provides a pulsed ground signal when cranking/running (use noid light or oscilloscope).
6. Continuity and shorts: check continuity from injector pin to PCM pin; check for short to battery or ground and for high resistance/opens.
7. Injector substitution: swap injector #7 with a known-good injector from another cylinder and see if the code/misfire follows the injector (confirms injector) or stays with the cylinder (indicates wiring/PCM).
8. Scope the circuit: if intermittent and not obvious, use an oscilloscope to capture injector drive waveform for dropouts, noise or incorrect drive levels.
9. Repair wiring/connectors: repair damaged wiring, clean/replace connector pins or replace injector as indicated. Re-test and clear codes.
10. If wiring and injector check good and intermittent driver signals persist, consider PCM diagnostics or replacement after verifying all wiring and grounds.