Cause
Faulty EGR temperature sensor
The sensor measuring the temperature of recirculated exhaust gas, which the module uses to confirm that recirculation is actually happening. It is a flow check performed with a thermometer — gas flowing through the cooler and into the intake carries heat with it, so a temperature rise is the evidence that the valve did what it was told.
A faulty sensor therefore breaks the verification rather than the function. Recirculation may be working perfectly while the module concludes it is not, and it will store flow and performance codes accordingly. A flow code alongside a valve that demonstrably moves is worth pointing at this sensor before the valve or the passages are disturbed.
It sits in soot, which is what fails it. A coated element responds slowly rather than incorrectly, so correlation checks against a second sensor trip while each reading looks reasonable on its own. Watch how quickly it responds when recirculation is commanded, not what it reads at rest — a sluggish sensor is the finding, and a reading taken at one moment will not show it.
Typically a moderate job.
Codes this can cause (4)
Codes where this is a likely explanation first, rather than merely a possible one.
- P040B Exhaust Gas Recirculation Temperature Sensor A Circuit Range/Performance Likely for this code Moderate
- P040F Exhaust Gas Recirculation Temperature Sensor A/B Correlation Likely for this code Moderate
- P040D Exhaust Gas Recirculation Temperature Sensor A Circuit High Moderate
- P04D0 Exhaust Gas Recirculation Temperature Sensor C Circuit Low Moderate
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