P042E
PowertrainExhaust Gas Recirculation A Control Stuck Open
The EGR valve has been commanded shut but the ECU can see it's hung open, so exhaust gas keeps flowing into the intake when the engine doesn't want it. That's why these usually idle rough and feel flat. On most cars it's a carbon problem rather than a dead valve, and that's good or bad depending on how bad the gunk has got.
ⓘ Information only. This page provides general educational information about fault code P042E. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P042E mean?
P042E is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Exhaust Gas Recirculation A Control Stuck Open.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine management light on, sometimes with the car dropping into limp mode on a motorway pull
- • Lumpy idle when warm, often smoothing out for a second when you blip the throttle
- • Hesitation or a flat spot when you accelerate from low revs
- • Noticeably worse fuel economy, more obvious on a diesel
- • Occasional stalling at junctions or when coasting to a stop
- • Diesels can blow a bit of black smoke on acceleration when the valve sticks open
Possible causes
Causes commonly associated with P042E, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Carbon clogging the valve so it physically can't seat closed. This is the usual culprit, especially on diesels that do a lot of short urban trips and never get hot enough to burn the soot off
- 2. Mechanically worn or seized EGR valve where the plunger or pintle has stuck. Common on higher-mileage cars
- 3. Faulty position sensor inside the valve reporting the wrong position even when the valve is doing its job
- 4. Coked-up EGR passages or intake ports holding the valve open even after the valve itself is cleaned
- 5. Failed EGR solenoid or vacuum control on the older vacuum-operated setups
- 6. Wiring or connector trouble in the EGR circuit, corroded pins or chafed loom near the hot exhaust side
- 7. ECU software fault, rare, and only worth considering after the mechanical stuff checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read live data and compare commanded EGR position against actual position. If the actual stays open while commanded closed, the valve or its feedback is your problem
- 2. Pull every code that's stored. Misfire codes, boost faults or a P042F sitting alongside this usually point at the same coked-up valve
- 3. Get the valve off and look at it. Heavy black carbon on the seat that stops the plunger closing tells you most of what you need to know before you spend a penny
- 4. Check the EGR passages and the throat into the intake while the valve is off. A clean valve won't help if the port behind it is choked solid
- 5. Inspect the wiring and connector for corrosion, melted insulation or a loose pin, particularly on engines where the loom runs close to the manifold
- 6. With the valve out, test the solenoid and position sensor resistance with a multimeter and back-probe the supply and signal feeds with the loom connected
Common questions about P042E
How do I know if it's just dirty or the valve's actually dead? +
Take the valve off and have a proper look. If it's caked in black carbon and the plunger feels gritty or won't move smoothly by hand, that's a cleaning job and you've likely found your answer. If the valve looks reasonably clean but the live data still shows actual position stuck open against a closed command, you're looking at the internal position sensor or a seized mechanism, and that's a replacement. The deciding factor is whether the plunger moves freely once the soot is off.
Can I clean it myself instead of buying a new one? +
On plenty of cars, yes. Get the valve off, soak the carboned area in EGR or carb cleaner, and work the deposits off with a stiff brush or a pick. Don't blast cleaner into the electrical connector. The catch is the passage behind the valve. If that's blocked too you may need to clean into the intake manifold, which on some engines means stripping a lot more off. If the valve's mechanically worn or the sensor's failed, cleaning buys you nothing.
If I clear the code does it stay gone? +
Only if you actually fixed what caused it. Clear a P042E on a valve that's still gummed open and the light comes straight back within a few drive cycles, often before you've left your street. Clean or replace the valve first, then clear it and road-test. If it stays off after a proper warm-up run, you're sorted. If it returns immediately, the valve still isn't seating or the position sensor is lying.
What happens if I just leave it? +
It'll keep getting worse rather than fixing itself. A valve stuck open dumps exhaust into the intake all the time, which fouls the inlet, drags your economy down and on a diesel can soot up the DPF faster. Long-term you risk extra carbon spreading through the intake and, if the running stays rich or rough, damage to the cat. Some cars will sit in limp mode too, which is no fun on a motorway slip road. Cheaper to deal with it while it's still a cleaning job.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →