Powertrain, generic · Auxiliary emission controls

P040C EGR Temperature Sensor A Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

EGR temperature sensor A measures the gas temperature in the EGR path – for cooler monitoring, component protection and the EGR model. Whether it sits before or after the cooler depends on the maker: GM diesels have sensor A after and B before the cooler, Ford diesels sensor B after it. Like a coolant sensor it is an NTC, so a low voltage means hot. P040C means the signal is below its lower limit – very hot or a signal wire shorted to ground. Thresholds: GM's Duramax LML below 0.46 V for 5 s, GM 2014 below 0.14 V, GM 2018 a resistance below 404 Ω, Ford diesel below 0.69 V for 5 s; MIL after two trips. A substitute value is used and the EGR cooler check is suspended.

Likely causes

Signal wire shorted to ground (chafed on the exhaust)
Sensor shorted internally
Water in the connector
Actual extreme gas temperature (EGR cooler faulty)

Symptoms

  • Check engine light on
  • Usually no change in driving
  • Substitute value used, EGR cooler check suspended

Repair estimate

DifficultyEasyDIY possible
Parts and labour€50–250
Time0.5–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

egr temperature sensor aegr coolersensor wiringengine control module

Related codes

P040AP040BP040DP040EP041C

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, fordservicecontent.com.