P2ACE

Code

Generic P — Powertrain

Reductant Temperature Sensor B Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 20 EN: 30 RU: 24

AI status

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Page language: EN

Causes

Short to ground in the sensor signal or power circuit
Poor or corroded connector or pin at the sensor
Failed/redundant Reductant Temperature Sensor B (internal short or low output)
Open or high-resistance wiring (intermittent connection)
Blown fuse or removed/disabled supply or ground
Contamination of sensor (urea crystals, corrosion) affecting reading

Symptoms

Malfunction Indicator Lamp (MIL) / check engine light illuminated
Stored freeze-frame and P2ACE code(s)
Possible SCR/aftertreatment warning or reduced emissions system performance
Reduced engine power or limp mode in some vehicles (aftertreatment protection)
Inability to perform/complete DEF dosing or regeneration events
Possible dashboard message indicating DEF system fault

What to check

Read and record freeze-frame and live data for reductant temperature sensors (A and B) with a scan tool
Compare sensor B reading to sensor A and to ambient; note if B is stuck at very low value
Visually inspect sensor connector, pins and wiring for damage, contamination or corrosion
Perform a wiggle test on wiring while monitoring live data to reveal intermittent faults
Backprobe the connector and measure signal voltage, reference supply and ground with key ON (engine OFF) per wiring diagram
Measure sensor resistance (with connector disconnected) and compare to expected type behavior (thermistor: resistance changes with temperature)

Signal parameters

Typical thermistor-type reductant temperature sensor: resistance changes with temperature (higher resistance at low temp, lower at high temp); exact values are manufacturer-specific
Expected signal voltage range (varies by design): approx. 0.1–5.0 V; a constant near 0.0–0.5 V typically indicates 'low circuit' or short to ground
With connector disconnected, infinite/open or very high resistance indicates open circuit; a near-zero ohm reading indicates short to ground
Compare Sensor B vs Sensor A readings: large discrepancy suggests wiring/sensor fault on B

Diagnostic algorithm

Use a scan tool to confirm P2ACE is active and capture freeze-frame and live reductant temperature readings for Sensor B and Sensor A.
Visually inspect sensor B, connector, and harness for damage, contamination (urea crystals) or corrosion. Clean or replace connector as needed.
With ignition ON (engine OFF), backprobe the sensor connector and measure: a) signal voltage, b) reference supply voltage (if applicable), and c) ground continuity. Compare to expected behavior: signal stuck low or 0V indicates short to ground or no supply.
With connector disconnected, measure sensor resistance at ambient temperature. If the sensor is a thermistor, verify resistance is sensible for ambient temperature (manufacturer spec). A near-zero resistance indicates internal short; infinite/open indicates open sensor.
Perform a wiggle/pressure test on the harness while monitoring live data to find intermittent wiring faults.
Check for shorts to ground/voltage using an ohmmeter between the signal wire and chassis ground; repair damaged wiring or replace pigtails as needed.
Repair or replace the sensor or harness as indicated. Replace corroded connectors and any damaged wiring; ensure proper sealing against DEF contamination.
Clear codes, perform a functional test and a road test or required drive cycle. If code returns, expand diagnosis to power/ground circuits and control module outputs, and consult vehicle-specific wiring diagrams and manufacturer technical service information.

Likely causes

Damaged/chafed wiring shorted to chassis ground near sensor
Corroded/loose connector at the reductant temperature sensor
Failed sensor element (thermistor or internal electronics)
Connector contamination from DEF/urea crystallization
Faulty or missing reference supply (fuse/relay) to sensor

Fault status

⚠️ Status

P2ACE — Reductant Temperature Sensor B Circuit Low: controller detects abnormally low voltage/reading from DEF/reductant temperature sensor B; inspect for short to ground, connector/corrosion, or failed sensor.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-1.5 hours