P042E
Gas Recirculation A Control Stuck OpenP042E is a generic OBD-II powertrain diagnostic trouble code: Gas Recirculation A Control Stuck Open. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P042E means
P042E is a SAE generic powertrain code that sets when the PCM/ECM detects that the Exhaust Gas Recirculation (EGR) 'A' valve is stuck in the open position — meaning the valve is not closing on command when the ECM requests it to close. The EGR system recirculates a metered portion of exhaust gas back into the intake manifold to lower peak combustion temperatures and reduce NOx emissions. When the valve fails to close, unmetered exhaust gas continues to enter the intake charge regardless of operating conditions.
A stuck-open EGR valve dilutes the intake charge with inert exhaust gases at times when no EGR flow is desired — such as cold start, idle, and wide-open throttle — causing rough idle, hesitation, misfires, and reduced power. Because exhaust gas contains carbon monoxide and particulates, prolonged exposure of the intake and combustion chamber can accelerate carbon buildup on intake valves and piston crowns. The condition illuminates the MIL and stores a freeze-frame; on some vehicles with strict emissions monitoring, it may also trigger a torque reduction or limited-operation strategy.
Common root causes are heavy carbon deposits locking the EGR valve pintle open, a failed EGR valve actuator (vacuum-operated or electric stepper), cracked or collapsed EGR vacuum lines, a faulty EGR position sensor providing incorrect feedback, or a short/open in the EGR control circuit. Rarely, PCM software or a wiring harness fault can mimic a stuck-open condition.
Common causes
Most-frequently reported root causes when P042E is logged.
-
1
Carbon/soot deposits holding the EGR valve pintle stuck open
-
2
Failed or seized EGR valve (mechanical or electromechanical actuator failure)
-
3
Broken, cracked, or disconnected EGR vacuum supply or control line
-
4
Faulty EGR valve position sensor providing incorrect (always-open) feedback
-
5
Open or short circuit in the EGR valve control wiring harness
-
6
Faulty EGR solenoid or driver circuit inside the PCM
-
7
Coolant or oil contamination of the EGR valve or its actuator bore
-
8
Clogged EGR cooler causing back-pressure that prevents valve closure
Symptoms drivers notice
How to diagnose P042E
A typical diagnostic flow when this code is present.
-
1
Connect a scan tool and record all stored DTCs plus freeze-frame data; note engine coolant temperature and load conditions at time of fault
-
2
Inspect the EGR valve and connecting pipes visually for heavy carbon fouling, cracking, or mechanical damage; check vacuum lines (if vacuum-operated) for cracks or disconnection
-
3
Command the EGR valve closed via bidirectional scan tool output control and observe the EGR position sensor PID — if position does not change, the valve or its actuator is mechanically stuck or electrically open
-
4
Check EGR valve control circuit wiring: test for proper voltage and ground at the valve connector, and inspect for chafed or corroded wires between the valve and PCM
-
5
If wiring and power supply are good, remove and inspect the EGR valve for stuck or seized pintle; clean with EGR-safe carbon cleaner or replace the valve
-
6
After repair, clear codes and perform a drive cycle that exercises the EGR monitor; confirm no reoccurrence and that EGR position PID tracks commanded position
-
7
If the fault returns immediately after valve replacement, inspect the EGR position sensor separately and check for PCM-side driver fault using a known-good ECM or manufacturer-specific testing procedure
Vehicles where we've handled P042E
Platforms in our catalogue with confirmed P042E coverage.
Related powertrain codes
- P0400 — Exhaust Gas Recirculation Flow Malfunction
- P0401 — Exhaust Gas Recirculation Flow Insufficient Detected
- P0402 — Exhaust Gas Recirculation Flow Excessive Detected
- P0403 — Exhaust Gas Recirculation Circuit Malfunction
- P0404 — Exhaust Gas Recirculation Circuit Range/Performance
- P0405 — Exhaust Gas Recirculation Sensor A Circuit Low
Frequently asked questions
Is it safe to drive with code P042E set?
Short-term driving is generally possible because the engine will still run, but a stuck-open EGR valve causes rough idle, poor power, and increased fuel consumption. Prolonged operation accelerates carbon buildup in the intake manifold and on intake valves, and on some vehicles the ECM may reduce torque output. It is advisable to diagnose and repair the fault promptly rather than driving for extended periods.
Can heavy carbon deposits alone cause P042E without the valve being physically broken?
Yes. Carbon buildup is the most common cause of a stuck-open EGR valve, particularly on high-mileage engines or those that do a lot of short-trip driving. In many cases the valve can be removed, cleaned with an EGR-safe solvent or carbon cleaner, and reinstalled, resolving the code without replacing the valve.
What is the difference between P042E and P0401 or P0404?
P0401 indicates insufficient EGR flow (the system is not delivering enough recirculation), while P0404 indicates the EGR valve position is out of its expected range. P042E specifically means the valve position sensor and/or mechanical feedback confirms the valve is stuck in the open state when the ECM has commanded it closed — it is a control-response failure rather than a flow-volume fault.
Does P042E affect emissions testing (MOT/smog check)?
Yes. Because P042E stores as an active emissions-monitor fault and illuminates the MIL, the vehicle will fail an OBD-based emissions inspection in any jurisdiction that checks for active DTCs or a lit MIL. The fault must be repaired and the EGR monitor must complete and pass before the vehicle can pass an emissions test.
Disabling P042E in software
RaceTune can permanently disable P042E — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P042E disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C50 verified 1 software version
- Bosch EDC17C74 verified 1 software version
- Bosch EDC17CP09 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P042E in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file