P2042: Reductant Temperature Sensor A Circuit
What to do
No effect on how the car drives. Worth repairing before winter rather than after: the system will not dose while it is unsure the fluid has thawed, and prolonged non-dosing is what eventually restricts the vehicle. If the fault appeared in cold weather, mention that.
What this code means
A fault in the sensor measuring the temperature of the reductant solution. The reason a urea system cares so much about temperature is one of its least-known properties, and it explains a great deal of the hardware bolted to the tank.
Reductant solution freezes at about minus eleven degrees Celsius. That is an ordinary winter night across much of the world, not an extreme, so these systems are built expecting it: the tank carries a heater, the supply lines are heated, and the module will not attempt to dose until it is satisfied the fluid is liquid. Freezing does the fluid no harm — it thaws and works normally — but dosing slush is a reliable way to produce the crystallised deposits that block an injector.
So this sensor governs whether dosing is attempted at all in cold weather. Without a trustworthy reading the module takes the conservative route and suspends dosing, which starts the sequence described under P2047. A temperature sensor fault is therefore considerably more consequential in January than in July, and worth reporting with the season attached.
Likely causes
Start here
- Faulty reductant temperature sensor · moderate
- Corroded or loose connector · easy
Less common
- Faulty reductant tank heater · moderate
- Open circuit in sensor wiring · moderate
- Road damage to underfloor wiring · moderate
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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