Diesel Trouble Codes

P042E — Exhaust Gas Recirculation Control Stuck Open (L5P Duramax)

Diagnostic reference for P042E on L5P Duramax (2017–present).

Updated September 2, 2026

What it means

The EGR control circuit reports the valve stuck in the open position.1

Most likely causes

  1. EGR valve stuck open due to carbon fouling / mechanical binding — Valve pintle or seat carboned, preventing closure; position feedback indicates open.12
  2. EGR valve position sensor / actuator feedback fault — Position sensor or electric actuator reporting incorrect position; ECM interprets as stuck open.1
  3. EGR control circuit electrical fault — Wiring, connector corrosion, or control module issue causing false stuck-open report.1
  4. EGR cooler / passages restriction causing flow anomaly — Severe restriction can affect valve operation and feedback; often accompanies low-flow codes.2
  5. ECM calibration / learned adaptation issue — Adaptation drift causing incorrect stuck-open determination.1

How to diagnose

  1. Verify code and freeze frame; confirm P042E active on L5P Duramax with EGR valve + cooler present.
  2. Inspect EGR valve pintle and seat for carbon buildup and mechanical binding; check valve moves freely.
  3. Check EGR position sensor/actuator feedback and supply/return signals; compare commanded vs actual position.
  4. Inspect EGR valve electrical connector and wiring for corrosion, damage, or intermittent faults.
  5. Inspect EGR cooler and passages for excessive soot restriction that can affect valve operation.
  6. Perform ECM EGR functional test / bi-directional control to observe valve response and position data.
  7. Review related EGR codes (e.g., P0401 low flow) and intake soot restriction symptoms.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by region and shop; obtain local quotes.

When to see a pro

If diagnosis requires internal EGR component removal, high-pressure fuel system access, or ECM reprogramming, have a qualified diesel technician perform the work.

Sources

  1. Curated DTC seed — L5P Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — L5P Duramax (curated) ↩︎ ↩︎

Watch a repair

Third-party videos, not ours — for illustration. Confirm anything against the factory service information for your truck.

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