Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Garage soon
Code P2457: EGR cooler performance
P2457 means: exhaust gas recirculation (EGR) cooler performance.[1][2][3] The control unit checks that the EGR cooler lowers the temperature of the recirculated gases as much as expected. TaT describes it as a plausibility fault: the signal is within its electrical range, but its value does not match what is expected. The control unit estimates the expected temperature from engine load, coolant temperature and the commanded EGR flow, and stores the code if the cooler falls short for a monitored period.[1][2]
What code P2457 means
The control unit checks that the EGR cooler lowers the temperature of the recirculated gases as much as expected. TaT describes it as a plausibility fault: the signal is within its electrical range, but its value does not match what is expected. The control unit estimates the expected temperature from engine load, coolant temperature and the commanded EGR flow, and stores the code if the cooler falls short for a monitored period.[1][2]
Wikipedia explains that EGR gas is usually cooled in a heat exchanger, which allows a greater mass of gas to be recirculated and reduces NOx further, and that cooled EGR components withstand sudden temperature changes, which can eventually cause coolant leaks.[4]
Car Verif rates it as moderate severity (“plan it”) and says the car can be driven with caution. It is a generic code of the OBD-II standard (it starts with P2), with the same definition on any brand.[2][5]
Original definition (SAE J2012): Exhaust Gas Recirculation Cooling System Performance[1][2][3]
Causes of P2457
From most to least likely, according to the sources.
- 1EGR cooler blocked internally: TaT refers to soot and oil vapours that build up in the core, insulating it and restricting flow; Car Verif adds scale deposits that reduce coolant flow. Car Verif lists it as the most frequent cause.[1][2]
- 2Lack of coolant or a coolant leak, which prevents the gases from being cooled properly.[2]
- 3Faulty temperature sensor giving wrong readings even though the cooler works properly.[2]
- 4Damaged wiring or connectors on the sensor.[2]
- 5Dirty EGR valve, which indirectly affects cooler performance.[2][6]
- 6Control unit misreading the EGR data, considered unlikely.[2]
Symptoms
- Engine fault warning light on.[2]Engine warning light: faults that cause it
- Loss of power.[2]Less power: faults that cause it
- Higher fuel consumption.[2]Uses more fuel: faults that cause it
- Black smoke from the exhaust.[2]Black smoke: faults that cause it
- Possible engine overheating, according to Car Verif.[2]Overheating: faults that cause it
How to diagnose P2457
In order: from the most likely and cheapest to check to the most expensive.
- 1Read all the codes, note the associated ones, clear them and carry out a road test to see whether they return.[2]
- 2Check the coolant level in the expansion tank and observe whether it drops quickly, which points to a leak. Do not open the circuit with the engine hot.[2]
- 3Inspect the EGR cooler and its surroundings for soot, leaks or corrosion, and photograph anything suspicious.[2]
- 4Check the wiring and connectors of the EGR temperature sensor: that they are securely fixed and free of rust or damage.[2]
- 5Clean the EGR valve and the cooler with a suitable product, if the manufacturer allows it, and refit them.[2][6]
- 6With live data, compare the EGR inlet and outlet temperatures at idle and under acceleration. A very small difference confirms the fault and may also indicate a sensor problem.[2]
- 7After any work, clear the codes and drive about 50 km in varied conditions. If P2457 returns, take your notes and photos to a diesel or emissions specialist.[2]
Can I keep driving with P2457?
Garage soon
Car Verif rates it as moderate severity (“plan it”) and says the car can be driven with caution; TaT does not rate the severity. However, the symptoms it cites include loss of power and possible overheating, and Wikipedia mentions coolant leaks in cooled EGR components. If the coolant level drops or the temperature rises, do not delay.[2][4]
Parts related to code P2457
The parts that most often cause this code. The code points to the circuit, not always the part: diagnose before you buy.
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Documented faults related to P2457
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
EGR valve: the most serious faults by engine and car
- Critical severityFrequency: Very frequentBMW B47EGR cooler leaks with risk of engine fireYes: the EGR valve cooler can suffer internal coolant leaks which, mixed with soot and oil, can reach combustion temperatures; BMW has launched several technical campaigns since 2018 to inspect and replace it because of the risk of engine fire.Repair (garage): €500–€1,500
- Critical severityFrequency: Very frequentBMW N57EGR cooler leaks with risk of engine fireYes: like the N47 and B47, the N57 is covered by BMW's service campaign for EGR cooler leaks, which can mix coolant with soot and oil to combustion temperatures. BMW checks free of charge the 6-cylinder engines built between July 2012 and June 2015 because of the fire risk.
- High severityFrequency: Very frequentOM651EGR and particulate filter clogging, and emissions software updatesThe particulate filter and EGR clog up with short journeys, as on any diesel with these systems. In addition, Germany's KBA required software updates on several models with this engine between 2018 and 2021 because of a function that reduced EGR outside a temperature range.Repair (garage): €800–€2,500
- Medium severityFrequency: Very frequentOM642Emissions defeat device (AdBlue/EGR) and software update campaignGermany's KBA found indications of emissions manipulation in cars with the OM642 engine (alongside the OM651): AdBlue dosing and the EGR changed between the test bench and the road. Mercedes-Benz denied it, but in 2018 it recalled hundreds of thousands of diesels in Europe.
Engine sensors: the most serious faults by engine and car
- High severityFrequency: Occasional2.0 DTI and 2.2 DTIVP44 injection pump and air mass meter failureGerman Wikipedia documents recurring failures of the Bosch VP44 injection pump and the air mass meter in the early years of this engine. An owner testimony for this engine describes the pump being replaced at 192,500 km, at a cost the owner calls «prohibitive».
- Medium severityFrequency: Common2.0 TDIClogged particulate filter or faulty pressure sensorThe 2.0 TDI's particulate filter clogs if the car mostly makes short journeys, because it never gets to regenerate; sometimes the fault is just the differential pressure sensor. Cleaning it costs around €200 and replacing it, €800 to €3,000.Repair (garage): €800–€3,000
- Medium severityFrequency: Common1.4 and 1.6 8vCrankshaft position sensor failure (TDC sensor)The crankshaft position sensor (capteur PMH, or TDC sensor) appears repeatedly in the reliability sources for the Clio II, the Kangoo I and the Dacia Logan I with this engine, with hard cold starting or stalling as the main symptoms. It is a cheap part, but the failure can leave you stranded.
- Medium severityFrequency: Common1.4 and 1.6 16vCrankshaft position sensor failureThe crankshaft position sensor (capteur PMH) appears repeatedly in the reliability sources for almost every generation with this engine, with hard cold starting, stalling or the car cutting out unexpectedly. It is a cheap part, but the failure can leave you stranded.
Frequently asked questions
What does the EGR cooler do?
It cools the exhaust gases before they return to the intake. According to Wikipedia, this cooling allows a greater mass of gas to be recirculated and so reduces NOx further; it also uses the heat to warm the coolant sooner after a cold start.[4]
Does P2457 mean the EGR valve needs replacing?
No. Car Verif places the blocked cooler as the most frequent cause, with a dirty EGR valve as a less common cause that affects the cooler indirectly. A faulty temperature sensor or a coolant loss can also be the cause.[2]
Can I keep driving with P2457?
Car Verif says the car can be driven with caution and rates it as moderate severity. If you notice the coolant dropping, the temperature rising or the car losing power, take it to a workshop without waiting.[2]
Will I pass the MOT with code P2457?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[7]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- P2457 - Exhaust Gas Recirculation Cooling System Performance | TaTThe Automotive Technician (TaT) · Technical documentation · consulted 31 October 2026
- Code défaut P2457 — Émissions auxiliaires / EGRCar Verif · Technical documentation · consulted 31 October 2026 · in French
- p2457 Generic DTC: Exhaust Gas Recirculation Cooling System PerformanceDTCSearch.com (OBD Solutions) · Technical documentation · consulted 31 October 2026
- Exhaust gas recirculationWikipedia · Other source · consulted 31 October 2026
- On-board diagnosticsWikipedia · Other source · consulted 31 October 2026
- ¿Qué es el sistema antipolución del coche y qué averías puede sufrir?RACE · Motoring press · consulted 31 October 2026 · in Spanish
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish