P20AC code meaning
Reductant Metering Unit Temperature Sensor Circuit
Powertrain system Generic code P20xx codes Check engine light
What P20AC means
P20AC is the general circuit code for the temperature sensor built into the reductant metering unit, meaning the DEF supply or dosing module that pressurises the fluid. The control unit typically relies on this value to judge whether the module has thawed and may start pumping. The code stands for an electrical fault the software cannot assign to a low or high signal; those cases carry their own numbers, P20AE and P20AF. No manufacturer documents P20AC publicly. Hino, for example, files faults of its DEF pump temperature sensor under the maker-specific P142A instead. CARB requires such inputs to be watched continuously for circuit continuity. Drivers see a DEF or engine warning and, if it is ignored, speed or restart limits.
P20AC 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 P20AC
- Malfunction indicator or DEF/SCR warning lamp on
- Dosing delayed or stopped in cold weather
- Inducement countdown with speed or restart limit
Common causes of P20AC
- Most likelyCorroded or loose connector at the DEF supply/metering module
- PossibleDamaged sensor wiring between module and control unit
- PossibleTemperature sensor inside the metering unit failed (usually replaced with the module)
- Less likelyInput fault in the dosing or engine control unit
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant metering unitReductant metering temp sensor
What each part of P20AC 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. |
| AC | The exact fault in that area. |
What to do next
- Note P20AC 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 P20AC
What does P20AC mean?
P20AC means "Reductant Metering Unit Temperature Sensor Circuit". P20AC is the general circuit code for the temperature sensor built into the reductant metering unit, meaning the DEF supply or dosing module that pressurises the fluid. It is a generic code, so it means the same on every make.
Is it safe to drive with P20AC?
Drive gently and only to a workshop. With P20AC the car can go into limp mode (reduced power) to protect itself.
Will P20AC fail an emissions test?
Yes, it can. P20AC 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 P20AC to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P20AC clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.