Powertrain, generic · Auxiliary emission controls

P040B EGR Temperature Sensor A Circuit Range/Performance

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. P040B is its plausibility check: after a cold start the sensor must warm up once hot exhaust flows. Ford diesels set the code if it rises by less than 10 °C after load; GM diesels if it barely changes after at least 8 hours off and a defined EGR flow (MIL after two trips). A sooted sensor tip or a lack of EGR flow are typical causes.

Likely causes

Sensor sluggish, tip sooted
Sensor drifting or faulty
No EGR flow (valve or cooler blocked), sensor sees no heat
Contact resistance in the connector

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

P040AP040CP040DP040FP041BP0401

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