Cause
Faulty reductant temperature sensor
The sensor reporting the temperature of the AdBlue in the reductant system has failed.
Reductant is a urea solution injected into the exhaust to convert NOx, and its temperature is measured because it freezes at a temperature the car will routinely meet — about −11 °C. That is an ordinary winter night across most of Europe and North America.
The design accommodates freezing rather than preventing it. The tank is built so expanding ice does not damage it, and the vehicle is permitted to run without dosing while it thaws — so a delay before dosing begins on a cold morning is normal behaviour, not a fault. The system carries heaters, and this sensor is what decides when to use them and when dosing may safely resume.
Temperature matters for a second and less obvious reason: dosing quantity depends on the solution's concentration, and concentration is inferred from properties that vary with temperature. So a wrong reading produces a wrong dose rather than no dose — which is harder to detect and shows up as NOx conversion efficiency rather than as an obvious failure.
The consequence of leaving it is what makes this urgent. Emissions legislation requires the vehicle to enforce its own aftertreatment: a persistent reductant fault leads to reduced power and eventually a refusal to restart, on a mandated countdown the dashboard will state in miles. It is drivable now and it will not stay that way.
Typically a moderate job.
Codes this can cause (21)
Codes where this is a likely explanation first, rather than merely a possible one.
- P2042 Reductant Temperature Sensor A Circuit Likely for this code Moderate
- P2043 Reductant Temperature Sensor A Circuit Range/Performance Likely for this code Moderate
- P2044 Reductant Temperature Sensor A Circuit Low Likely for this code Moderate
- P2045 Reductant Temperature Sensor A Circuit High Likely for this code Moderate
- P2046 Reductant Temperature Sensor A Circuit Intermittent Likely for this code Moderate
- P209F Reductant Tank Heater Control Circuit Performance Likely for this code Moderate
- P20BA Reductant Heater A Control Circuit Performance Likely for this code Moderate
- P20BE Reductant Heater B Control Circuit Performance Likely for this code Moderate
- P20C2 Reductant Heater C Control Circuit Performance Likely for this code Moderate
- P20C6 Reductant Heater D Control Circuit Performance Likely for this code Moderate
- P24FF Reductant Temperature Too High Likely for this code Moderate
- P2ACC Reductant Temperature Sensor B Circuit Likely for this code High
- P2ACD Reductant Temperature Sensor B Circuit Range/Performance Likely for this code High
- P2ACE Reductant Temperature Sensor B Circuit Low Likely for this code High
- P2ACF Reductant Temperature Sensor B Circuit High Likely for this code High
- P2AD0 Reductant Temperature Sensor B Circuit Intermittent Likely for this code High
- P2ADA Reductant Tank Temperature Sensor B Circuit Range/Performance Likely for this code High
- P2ADB Reductant Tank Temperature Sensor B Circuit Low Likely for this code High
- P2ADC Reductant Tank Temperature Sensor B Circuit High Likely for this code High
- P2ADD Reductant Tank Temperature Sensor B Circuit Intermittent/Erratic Likely for this code High
- P2ADE Reductant Tank Temperature Sensor B Circuit Likely for this code High
Information, not instruction
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