P2042 code meaning
Reductant Temperature Sensor A Circuit
Powertrain system Generic code P20xx codes Check engine light
What P2042 means
P2042 concerns reductant temperature sensor A, which is a different part from the tank temperature sensor of P205A ff. The makers that document it place it outside the tank: Deutz assigns P2042 to the DEF temperature sensor of the SCR system (J1939 SPN 4337), while its tank sensor (SPN 3031) uses P205A; failure type 13 marks an open circuit, F0 a ground fault. Volvo and Mack describe P2042-01 (US17/OBD16 engines) as a test of the temperature sensor in the DEF pump and warn in KC-2015 that low battery voltage with ambient and tank below 0 °C logs it with nothing wrong; then the pump must not be replaced. Hino also separates tank and pump sensors. Short to ground and to battery are P2044 and P2045. Drivers see the MIL and a DEF warning.
P2042 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P2042
- MIL and DEF system warning
- DEF heating or dosing may be restricted
Common causes of P2042
- Most likelyOpen circuit or loose connector at the pump/supply module
- PossibleFalse setting at low battery voltage in frost (Volvo/Mack)
- PossiblePoor sensor ground
- Less likelyTemperature sensor in the pump unit defective
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant temperature sensorReductant pump
What each part of P2042 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| 42 | The exact fault in that area. |
What to do next
- Note P2042 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P2042
What does P2042 mean?
P2042 means "Reductant Temperature Sensor A Circuit". P2042 concerns reductant temperature sensor A, which is a different part from the tank temperature sensor of P205A ff. It is a generic code, so it means the same on every make.
Is it safe to drive with P2042?
Drive gently and only to a workshop. With P2042 the car can go into limp mode (reduced power) to protect itself.
Will P2042 fail an emissions test?
Yes, it can. P2042 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P2042 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P2042 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.