P042F
Exhaust Gas Recirculation A Control Stuck ClosedP042F is a generic OBD-II powertrain diagnostic trouble code: Exhaust Gas Recirculation A Control Stuck Closed. It is logged by the engine control unit when the egr monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P042F means
P042F — Exhaust Gas Recirculation A Control Stuck Closed — is set by the ECM/PCM when the EGR valve position feedback indicates the valve has failed to open, or opens significantly less than commanded, over a monitored drive cycle. The EGR system recirculates a controlled portion of exhaust gas back into the intake manifold to lower combustion temperatures and reduce NOx emissions. When the valve is stuck closed, no exhaust gas is recirculated, combustion temperatures rise, and NOx output exceeds regulatory limits.
On diesel engines the EGR valve is typically an electrically actuated butterfly or poppet valve with an integrated position sensor (potentiometer or Hall-effect). The ECM commands a position, reads back the sensor signal, and compares the two. If the delta exceeds the calibrated threshold — for example, 10% error held for several seconds — the fault is set and the MIL illuminates. Carbon build-up in the EGR passage or on the valve seat is the single most common cause on high-mileage diesels.
The vehicle usually remains fully drivable because the engine management system compensates through injection timing and throttle. However, running indefinitely with EGR disabled causes elevated NOx emissions, possible turbocharger stress from altered exhaust backpressure, and on some architectures can trigger a torque derate after repeated fault confirmations.
Common causes
Most-frequently reported root causes when P042F is logged.
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1
Carbon/soot build-up on EGR valve seat preventing opening
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2
Failed EGR actuator motor or solenoid (electrically open or shorted)
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3
Damaged or corroded EGR valve position sensor / feedback potentiometer
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4
Wiring harness chafing, broken wire, or corroded connector at EGR valve
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5
Blocked EGR cooler causing excessive back-pressure that holds valve closed
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6
Failed EGR vacuum solenoid (on vacuum-actuated valves)
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7
ECM internal driver fault or corrupt EGR calibration table
Symptoms drivers notice
How to diagnose P042F
A typical diagnostic flow when this code is present.
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1
Connect a scan tool, record all stored codes and freeze-frame data; note engine load/rpm at fault confirmation
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2
Inspect EGR valve connector and harness for corrosion, chafing, or spread terminals; repair any wiring faults
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3
Use live data to command EGR valve open and monitor position feedback — if position does not change, the valve or its actuator has failed
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4
Remove EGR valve and inspect for heavy carbon fouling; attempt manual actuation of the valve plate by hand — if stuck, clean or replace
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5
Check EGR cooler for blockage by measuring pressure drop across it; replace if restricted
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6
Verify EGR position sensor supply voltage and ground at the connector with a DVOM; compare signal voltage to manufacturer specification
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7
If actuator and wiring test good but fault persists, check for ECM software updates / TSBs before condemning the ECM
Vehicles where we've handled P042F
Platforms in our catalogue with confirmed P042F 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
Can I drive with P042F active?
Yes, the vehicle is typically drivable, but the EGR system is not functioning correctly. Prolonged operation increases NOx emissions and, on some ECM maps, may eventually trigger a torque derate. Repair promptly.
Will cleaning the EGR valve fix P042F?
In many cases on high-mileage diesels, yes — carbon fouling is the most common cause. Remove the valve, clean with EGR/throttle cleaner, verify the plate moves freely, and reinstall. Clear the code and perform a drive cycle to confirm the fix.
Does P042F always mean the valve is physically stuck?
Not always. A faulty position sensor can report the valve as closed even when it is mechanically opening. Always verify with live data commands before replacing the valve itself.
Is P042F specific to diesel engines?
No. P042F is an SAE generic code that applies to any gasoline or diesel engine with an EGR system. However, it is disproportionately common on diesel engines because of higher soot loads that foul EGR passages quickly.
Disabling P042F in software
RaceTune can permanently disable P042F — 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 P042F 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 P042F in your scan?
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