P04D2 — EGR Temperature Sensor C Circuit Intermittent/Erratic

Diagnostic algorithm

1. Retrieve and record freeze frame and freeze data, then clear codes. Attempt to re-run and reproduce the fault under conditions reported in freeze data.
2. Monitor live data for EGR temp sensor C (raw voltage and temp) while starting, warming up and driving. Note any erratic jumps, dropouts or intermittent behavior.
3. Visually inspect the sensor, connector and wiring for damage, soot, corrosion or loose terminals. Repair or clean as needed.
4. Perform a wiggle test: with scan tool monitoring, move harness, connectors and related components to try to reproduce the intermittent fault. If code returns or signal changes, isolate wiring fault.
5. With ignition off, disconnect the sensor and measure continuity to ECM pins; check for opens, shorts to power/ground and correct resistance to ground. Repair any damaged wiring.
6. Measure sensor resistance vs. temperature (with sensor removed) using DVM or bench heat/cold if safe; compare to spec or check for smooth resistance change. Replace sensor if internal intermittent or out of expected behavior.
7. Backprobe with engine running to verify signal voltage and reference voltage are stable. Use an oscilloscope if available to catch brief spikes/drops that a DVM may miss.
8. If wiring and sensor test good and intermittent persists, check ECM harness connector and grounds. Refer to wiring diagrams for pin-to-pin verification.
9. After repairs or replacement, clear codes and perform a road test and extended scan-tool monitoring to confirm the issue is resolved and code does not return.
10. If all vehicle-side checks pass and intermittent continues, consider ECM input fault diagnosis or replacement following manufacturer procedures.