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.

Real-world scan data

Seen in

1,238

scans in the past year

Found in

0.2%

of scans

0.3%

of scans that found faults

Appears alongside · share of P042F scans

P0401in 43.7% of scans

P042Ein 27.9% of scans

P0645in 24.0% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P042F yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX