Faulty reductant metering unit temperature sensor; Damaged or corroded wiring harness or connector at the sensor; Short to ground in the sensor signal circuit; Open circuit in the sensor ground or signal circuit; Poor electrical connection at the powertrain control module; Extreme cold temperatures causing sensor signal out of range (if applicable)

DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20AE

P20AEReductant Metering Unit Temperature Sensor Circuit Low

Q: What does code P20AE mean?

Reductant Metering Unit Temperature Sensor Circuit Low. P20AE indicates that the powertrain control module has detected a low voltage signal from the reductant metering unit temperature sensor circuit, which monitors the temperature of the diesel exhaust fluid injector assembly. The sensor's signal is below the expected range, suggesting a short to ground, an open circuit, or a faulty sensor.

P20AE indicates that the powertrain control module has detected a low voltage signal from the reductant metering unit temperature sensor circuit, which monitors the temperature of the diesel exhaust fluid injector assembly. The sensor's signal is below the expected range, suggesting a short to ground, an open circuit, or a faulty sensor.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Reduced engine power or limp mode due to emissions system protection
Possible poor fuel economy or increased diesel exhaust fluid consumption
In rare cases, a no-start condition if the system interprets the fault as critical
Driver may notice a message on the dashboard indicating a reductant system fault

Common causes, most likely first

Faulty reductant metering unit temperature sensor
Damaged or corroded wiring harness or connector at the sensor
Short to ground in the sensor signal circuit
Open circuit in the sensor ground or signal circuit
Poor electrical connection at the powertrain control module
Extreme cold temperatures causing sensor signal out of range (if applicable)

How to diagnose and fix it

Verify the code with a scan tool and check for any related codes in the reductant system
Inspect the sensor connector and wiring for damage, corrosion, or loose pins
Measure the sensor resistance and compare to manufacturer specifications
Check for a short to ground or open circuit in the signal and ground circuits using a multimeter
If wiring is intact, replace the reductant metering unit temperature sensor
Clear the code and perform a road test to verify the repair
If the code persists, diagnose the powertrain control module or seek professional help

Common misdiagnosis traps for P20AE

A low signal code often results from a short to ground in the wiring, not a failed sensor, so always inspect the harness before replacing parts.
The reductant metering unit temperature sensor is sometimes integrated into the diesel exhaust fluid injector, requiring replacement of the entire unit rather than just the sensor.
Extreme cold weather can cause the sensor to read out of range temporarily, setting a false code that may not return after clearing.
Corrosion at the connector pins is a frequent culprit, especially in areas with road salt exposure, and can mimic a sensor failure.
This code can be set by a low battery voltage or poor ground connection, so check the vehicle's charging system and grounds first.

Can I keep driving with P20AE?

You can generally continue driving with this code, but avoid heavy loads or long trips until repaired, as the vehicle may enter limp mode and increase emissions. Monitor for other warning lights and address the issue promptly to prevent more severe reductant system faults.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.