P20AF code meaning
Reductant Metering Unit Temperature Sensor Circuit High
Powertrain system Generic code P20xx codes Check engine light
What P20AF means
P20AF means the metering unit temperature signal has risen above its permitted band. For an NTC thermistor, the likely design though not publicly confirmed for this part, that looks like an extremely cold module. Electrically it is usually an open signal or ground wire, a terminal backed out of the connector or a short to a voltage source. Corrosion deserves attention: Hino's bulletins SB-16-015 and SB-16-016 explain that frozen DEF can damage the pump and let fluid creep into the pump connector and SCR harness; Hino names its own P142A there, not P20AF. Believing the module frozen, the control unit holds back dosing and may keep heating. No maker publishes P20AF itself.
P20AF at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P20AF
- Module temperature shown far below ambient in live data
- DEF warning and delayed or missing dosing
- Further SCR codes if the harness is corroded
Common causes of P20AF
- Most likelyOpen signal or ground wire to the temperature sensor
- PossibleDEF intrusion and corrosion in the pump connector or harness
- PossibleSensor element in the metering unit open
- Less likelySignal wire shorted to a supply voltage
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 P20AF 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. |
| AF | The exact fault in that area. |
What to do next
- Note P20AF 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 P20AF
What does P20AF mean?
P20AF means "Reductant Metering Unit Temperature Sensor Circuit High". P20AF means the metering unit temperature signal has risen above its permitted band. It is a generic code, so it means the same on every make.
Is it safe to drive with P20AF?
Drive gently and only to a workshop. With P20AF the car can go into limp mode (reduced power) to protect itself.
Will P20AF fail an emissions test?
Yes, it can. P20AF 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 P20AF to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P20AF clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.