Powertrain, generic · Auxiliary emission controls

P040A EGR Temperature Sensor A Circuit

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. P040A is its general circuit code. No manufacturer document available to us uses it – GM and Ford report this sensor as P040B to P040E – so the description follows CARB's requirement to check input circuits for continuity and range. A substitute value is used and the EGR cooler check is suspended.

Likely causes

Connector or wire at the sensor (heat, corrosion)
Sensor faulty
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

P040BP040CP040DP040EP040FP041A

References: law.cornell.edu, fordservicecontent.com, gsi.ext.gm.com.