P040BPowertrain
Powertrain · SAE
EGR Temperature Sensor A Performance
Meaning
The EGR temperature sensor A reads implausible values: temperature does not rise during EGR operation or falls outside the physical range. On diesel engines this code may indicate EGR cooler blockage or an internal coolant leak.
Common causes
- Failed NTC/PTC temperature sensor (most common)
- EGR cooler heavily fouled with soot reducing gas flow
- Internal coolant leak inside EGR cooler (steam cooling exhaust gases)
- Intermittent wiring fault
- EGR valve stuck closed with no gas flow
Symptoms
- MIL illuminated
- EGR temperature monitoring degraded
- Possible white smoke if EGR cooler leaks coolant
- Reduced diesel engine performance
Severity
Moderate-to-high severity on diesel engines: an EGR cooler leaking coolant can cause engine damage if not addressed.
What to do
- Monitor EGR temperature sensor output versus coolant temperature at cold start
- Inspect EGR cooler for signs of coolant contamination (white deposits)
- Pressure-test the EGR cooler
- Replace the temperature sensor if the signal is flat or erratic