What it means
This code indicates a low voltage condition in the reductant metering unit temperature sensor circuit.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The temperature sensor in the DEF metering unit sends a signal used by the control module to monitor temperature and manage dosing. P20AE sets when the sensor circuit voltage is lower than expected, which can result from a short to ground or excessive resistance at a connection.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Save freeze-frame data and check live metering-unit temperature and sensor signal to see whether the low reading is present continuously.
- Inspect the sensor connector and harness for chafing, damaged insulation, corrosion, or a loose terminal that could pull the signal low.
- Check connector contact condition and wiring continuity, paying attention to high-resistance or corroded terminals.
- With power isolated as directed by the manufacturer, test the sensor circuit for a short to ground.
- Test the sensor and circuit against the manufacturer's specification to determine whether the fault is in the sensor, wiring, or module.
Common fixes
- Clean or repair corroded sensor connector terminals.
- Repair chafed sensor wiring that is contacting ground.
- Replace a damaged wire or sensor that tests shorted or out of specification.
- Repair the control module only if the sensor and wiring pass the manufacturer's tests.
Can I keep driving?
The vehicle may remain driveable, but a falsely low temperature signal can disrupt DEF metering and raise emissions; a restart countdown may follow. Follow dashboard warnings and arrange repair promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.