P042F
EGR A Control Stuck Closed
EGR / emissions
Generic OBD-II
Medium
What it means
P042F means the exhaust gas recirculation (EGR) valve is stuck closed and won't open when commanded. With no EGR flow, combustion runs hotter and can ping or knock under load, and NOx emissions rise. It won't stop the car from running, but the most common cause is carbon buildup — often fixable by cleaning the valve and passages.
Medium
Can I keep driving? Usually driveable; with EGR stuck closed you may notice pinging or knock under load and higher combustion temperatures, so repair before long-term driving.
Common symptoms
What you'll notice
- Check-engine light on
- Pinging or knock under acceleration and load
- Possible slight loss of power at higher speeds
- May fail an emissions test (raised NOx)
Common causes
Most likely first
- Carbon buildup in the EGR passages or valve holding it shutLikely
- Faulty or seized EGR valveCommon
- Loss of vacuum or electrical signal to the EGR valveCommon
- Faulty EGR vacuum-supply solenoid (on vacuum-operated systems)Less often
- Failed engine control module (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the EGR is being commanded but not opening.
- Remove and inspect the EGR valve and passages for carbon buildup; clean the valve, tube, and ports.
- Check the control signal or vacuum supply reaching the valve.
- Command the EGR open with a scan tool and watch for flow/valve movement.
- Replace the EGR valve if it won't open with a good signal. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P042F?+
Short-term yes, but with EGR stuck closed the engine can ping under load, which over time stresses the engine. Repair it before extended driving.
Can I just clear P042F?+
It will clear, but returns until the stuck EGR valve is cleaned or replaced. Cleaning carbon buildup often fixes it.
Related codes
Often seen with P042F
Read & clear P042F yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX