P2AD0: Reductant Temperature Sensor B Circuit Intermittent/Erratic

What it means

The reductant temperature B sensor signal drops out or jumps intermittently. Loose connector or noisy ground.

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 reports the temperature of the AdBlue/DEF aftertreatment fluid through an electrical signal. This code sets when the signal drops out or jumps intermittently, so the control module cannot rely on sensor B's reading.

Common causes

Most likely first.

1. Intermittent wiring or connector fault
2. Intermittent sensor fault
3. Poor ground connection

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 monitor sensor B's live temperature for dropouts or jumps, including while gently moving the harness.
2. Inspect the sensor B connector for looseness, corrosion, fluid ingress, or terminals with weak contact.
3. Trace the harness for chafing, broken conductors, or damage where it is exposed to heat or vibration.
4. Check the sensor B ground, supply, and signal connections for intermittent contact while observing the live reading.
5. If the wiring is sound, test sensor B against the manufacturer's specification for intermittent output.

Common fixes

• Secure the sensor B connector and clean or repair intermittent terminal contact.
• Repair damaged or chafed wiring in the sensor B circuit.
• Restore a poor sensor ground or circuit connection.
• Replace sensor B if its output remains intermittent with sound wiring.

Can I keep driving?

Driving may be possible at first, but the emissions system may show a NOx warning or begin a countdown that can restrict operation or prevent restarting. Diagnose it promptly, especially if a countdown appears.