What P042E means
Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx.
How the engine computer detects it
P042E means the position-controlled EGR valve A is more open than commanded and cannot be closed. GM's diesels of 2016/17 set it when the valve stays too far open despite maximum closing duty (about 1–8 s); the 2018 tables check after switch-off whether it is below 5 % within 2 s – both with MIL on the first trip. Ford gasoline engines compare the position with limits for 4 s, Ford diesels a deviation above 15 % for 25 s. Too much EGR causes rough idle, stalling and smoke; EGR control is switched off.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on (GM after one trip)
- Rough idle, stalling, starting problems
- Loss of power, possibly limp mode
- Diesel: smoke, higher soot load
Common causes
- Valve or disc coked, does not close Most likely
- Actuator motor, gear or return spring faulty Possible
- Position sensor in the valve reads wrong Possible
- Weak supply to the drive or connector fault Less likely
How to diagnose P042E
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: egr valve, egr valve actuator, egr valve position sensor, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 4
- Auxiliary emission controls
- 2E
- Specific fault
Questions drivers ask
Can I drive with code P042E?
Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.
Will my car pass an emissions inspection with P042E?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.