P042E — Exhaust Gas Recirculation Control Stuck Open — L5P Duramax

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

Updated October 15, 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.

Common mistake to avoid

Replacing the EGR valve without testing it. If the valve still moves freely, a carbon cleaning often fixes the flow code; and if it opens on command but the code stays, the blockage is in the passages or cooler, not the valve. Source: FleetRabbit — EGR valve problems and repair.

Parts and tools you may need

• Diagnostic scan tool with GM enhanced data and bi-directional control
• Digital multimeter
• EGR valve cleaning kit / approved solvent
• Torque wrench
• Safety gloves and eye protection

Tools you’ll need

• bi-directional scan tool — Commands EGR valve position and reads actual vs commanded feedback to confirm stuck-open condition on L5P Duramax.
• digital multimeter — Checks EGR valve position sensor supply, signal, and actuator control circuit voltages for electrical faults.
• borescope — Inspects EGR valve pintle, seat, and cooler passages for carbon fouling without disassembly.

Rough cost and difficulty

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

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.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources