P20AD code meaning
Reductant Metering Unit Temperature Sensor Circuit Range/Performance
Powertrain system Generic code P20xx codes Check engine light
What P20AD means
P20AD covers a metering unit temperature reading that is electrically valid but does not make sense. A typical check compares it after a long cold soak with other temperatures that ought to agree, or watches whether it climbs once the module heater or warm coolant has had time to act. Hino gives a practical yardstick in tech tip TT-16-014: with the engine at ambient temperature, DEF tank, DEF pump and coolant readings should lie within 8 °C (14 °F) of each other; Hino applies that to its coolant valve code P20B2, not to P20AD. No manufacturer publishes P20AD with its own limits. Because the verdict rests on behaviour over time, confirmation usually needs a complete drive cycle, and a skewed value can mislead the thaw and heating logic.
P20AD at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor1 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P20AD
- Warning lamp after a cold start or longer drive
- DEF dosing starts late or not at all in winter
- Live data shows module temperature out of line with tank and coolant
Common causes of P20AD
- Most likelyTemperature sensor in the metering unit drifted (reads plausible but wrong)
- PossibleComparison sensor (DEF tank or coolant temperature) itself faulty
- PossibleContact resistance in the connector shifting the signal
- Less likelyModule heating or coolant heating not working, so the expected rise never comes
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 P20AD 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. |
| AD | The exact fault in that area. |
What to do next
- Note P20AD 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 P20AD
What does P20AD mean?
P20AD means "Reductant Metering Unit Temperature Sensor Circuit Range/Performance". P20AD covers a metering unit temperature reading that is electrically valid but does not make sense. It is a generic code, so it means the same on every make.
Is it safe to drive with P20AD?
Drive gently and only to a workshop. With P20AD the car can go into limp mode (reduced power) to protect itself.
Will P20AD fail an emissions test?
Yes, it can. P20AD 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 P20AD to fix?
Difficulty: medium. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will P20AD clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.