Powertrain, generic · Auxiliary emission controls

P040D EGR Temperature Sensor A Circuit High

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. P040D means the signal is above its upper limit – very cold or, far more often, an open circuit (connector off, broken wire). Thresholds: GM's Duramax LML above 4.84 V for 5 s, GM 2014 above 4.98 V, GM 2018 a resistance above 1268 Ω (40 of 50 samples, MIL after two trips); Ford diesel lists the code without figures. A substitute value is used.

Likely causes

Connector off, broken wire or open circuit
Sensor open internally
Ground wire open or short to positive
Engine module input

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

P040AP040BP040CP040EP041D

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