P2457: EGR Cooler A Efficiency Below Threshold
P2457 means the engine computer has decided that exhaust gas cooler A is not removing enough heat from the recirculated exhaust. The check engine light comes on and emissions (NOx) rise, but the data does not describe a direct safety risk, so the code is a repair-soon problem rather than an emergency.
You can drive, but get it checked soon
The data lists no limp mode for this code, so the truck normally keeps running. The fault still raises NOx, and some engines may reduce EGR or power. If the cooler is also leaking, coolant loss or white smoke can follow, and driving on low coolant can damage the engine. Have it checked soon and watch the coolant level.
What it means
An EGR cooler is a small heat exchanger that uses engine coolant to cool the exhaust gas sent back into the intake (EGR stands for exhaust gas recirculation). The cooled gas helps keep NOx emissions down. The computer judges the cooler by comparing gas temperature with coolant temperature. Depending on the manufacturer, it measures how much heat the cooler removes or how hot the gas is when it leaves the cooler. If the result misses the limit, it sets P2457. The check usually runs on diesel engines and needs a drive cycle (a set pattern of driving) to complete, so the light may take a while to come on and to clear after a repair. Cooler A is the first cooler; the second cooler sets P241F instead.
Likely causes
- Cooler passages fouled with soot and lacquerVery likely
Deposits coat the inside of the cooler and insulate the gas from the coolant, so less heat is removed.
- Bypass flap stuck in bypass position or bypass module loosePossible
If the gas is routed around the cooler, it leaves hot; Ford traced this code on some 2018 to 2019 F-150 3.0 L diesels to loose screws in the bypass module.
- EGR outlet temperature sensor reading too highPossible
A sensor that reports more heat than is really there makes a healthy cooler look inefficient.
- Low coolant level or poor coolant flow through the coolerLess likely
Without enough coolant moving through it, the cooler cannot carry heat away.
- Monitor software misjudging efficiency (known on some trucks)Less likely
On some trucks, such as certain 2012 Hino models, the fix was a software update rather than hardware.
What you may notice
- Check engine light (malfunction indicator lamp) on
- Higher NOx emissions, sometimes reduced EGR or reduced power
- Coolant loss or white smoke if the cooler is also leaking
What to check, cheapest first
- 1Check the coolant level when the engine is cold and look for signs of leaks around the EGR cooler and hoses. · you can do it
- 2Read the code and freeze-frame data, and look for related codes such as P241F, P24A5, P245B, P0401 or P2425. · mechanic
- 3Check for software updates or service bulletins that apply to the vehicle's EGR cooler monitor. · mechanic
- 4Compare the EGR outlet temperature sensor reading with coolant temperature on a cold engine to see whether the sensor is accurate. · mechanic
- 5Inspect the bypass flap and bypass module for sticking, and check that the module's mounting screws are tight. · mechanic
- 6Inspect the cooler for soot and lacquer buildup and test coolant flow through it; clean or replace the cooler if it is fouled. · mechanic
Related codes
Frequently asked questions
Can I drive with P2457?+
Usually yes for a short time, since limp mode is not listed for this code. Watch the coolant level and temperature, and have it diagnosed soon because NOx emissions are elevated.
Can a loose gas cap cause P2457?+
No. The code concerns how well the EGR cooler removes heat, not the fuel system. It is mainly a diesel code, so a gas cap is not a cause.
Will P2457 pass an emissions test?+
Probably not. The check engine light is on and the code is emissions-related, so the fault generally needs to be repaired and the monitor must finish its drive cycle before a retest.
Can I fix P2457 myself?+
Checking coolant level is easy, but the repair is rated hard and not suited to most DIY work. Cooler cleaning or replacement can take from half an hour to about eight hours.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10