P2ACF: Reductant Temperature Sensor B Circuit High

What it means

Voltage on the reductant temperature B sensor signal line is above the expected window. Wire shorted to B+ or sensor open.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

Reductant temperature sensor B sends the control module a voltage signal for the temperature of the AdBlue/DEF aftertreatment fluid. This code sets when the signal voltage is above its expected range, which can result from a signal wire shorted to battery voltage, an open circuit, or a failed sensor.

Common causes

Most likely first.

1. Signal wire shorted to B+
2. Open or high-resistance signal/ground circuit
3. Sensor fault

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

1. Save freeze-frame data and check sensor B's live temperature for an implausibly high or fixed reading.
2. Inspect the sensor B connector and harness for loose terminals, corrosion, fluid ingress, or damaged insulation.
3. Check the signal, supply, and ground circuits for an open or high resistance using the vehicle wiring information.
4. With the circuit isolated as specified for the vehicle, test whether the sensor B signal wire is shorted to battery voltage.
5. Test sensor B and its circuit against the manufacturer's specification to pinpoint an open circuit or sensor fault.

Common fixes

• Reseat or clean loose and corroded sensor B connector terminals.
• Repair an open, high-resistance, or shorted wire in the sensor B circuit.
• Replace reductant temperature sensor B if it fails the specified test.

Can I keep driving?

Driving may be possible initially, but an active NOx warning or AdBlue/DEF countdown may lead to restricted operation or a no-start condition. Arrange repair promptly and heed any countdown shown.