P2457
EGR Cooler A Efficiency Below Threshold
Auxiliary emissions (EGR)
Generic OBD-II
Medium
What it means
P2457 means the EGR cooler isn't lowering the temperature of recirculated exhaust gas as much as the ECM expects. The cooler helps reduce combustion temperatures and NOx emissions, so poor efficiency — usually from carbon clogging or a failing cooler — raises emissions and can trip a reduced-power mode on diesels.
Medium
Can I keep driving? Usually drivable, but the EGR cooler isn't cooling exhaust gas enough — expect higher emissions and possible reduced power or limp mode on diesels, so get it checked soon.
Common symptoms
What you'll notice
- Check-engine light on
- Reduced power or limp mode (common on diesels)
- Higher exhaust/NOx emissions or a failed emissions test
- Coolant loss or overheating if the cooler is leaking internally
Common causes
Most likely first
- Clogged or carbon-fouled EGR cooler restricting flowLikely
- Internally leaking or failed EGR coolerCommon
- Stuck or sticking EGR valveCommon
- Low coolant flow through the cooler (thermostat, blockage, air pocket)Less often
- Inaccurate exhaust gas temperature sensor feeding the efficiency calculationLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for companion EGR and temperature-sensor codes.
- Inspect the EGR cooler for carbon clogging, cracks, or internal coolant leaks.
- Verify the EGR valve opens and closes freely without sticking.
- Confirm good coolant flow to the cooler (level, thermostat, no air pockets).
- Clean or replace the EGR cooler, then clear the code and re-test.
FAQ
Quick answers
Is it safe to drive with P2457?+
Short term usually yes, but if the cooler leaks coolant internally or the car drops into limp mode, get it fixed promptly to avoid overheating and higher emissions.
Can I just clear P2457?+
It will return once the ECM re-runs the EGR cooler efficiency test unless the actual cooling or flow problem is repaired.
Related codes
Often seen with P2457
Read & clear P2457 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