P21AD code meaning
Reductant Level Sensor C Circuit
Powertrain system Generic code P21xx codes Check engine light
What P21AD means
P21AD covers the electrical circuit of the third reductant level sensor, so it only exists on tanks with at least three level points. GM's 6.6L Duramax and 2014 Cruze diesel are such cases: the tank electronics test sensors 1 to 3 separately and pass each status to the ECM over CAN. GM uses the specific codes P21AF and P21B0 instead of this summary code. If P21AD shows up together with P21A8 and P203A, a shared supply, ground or the tank connector is far more likely than three failed sensors at once. Since the level information feeds the DEF range and refill warnings, drivers may see a missing or wrong range message besides the MIL. CARB asks for circuit monitoring of such inputs in 13 CCR 1968.2 (f)(15.2.1).
P21AD 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 P21AD
- Check engine light on
- DEF range message missing or implausible
- Further level sensor codes stored
Common causes of P21AD
- Most likelyFault in a supply, ground or connector shared by the level sensors
- PossibleLevel sensor C in the tank assembly failed
- PossibleSensor C signal wire damaged
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant level sensor
What each part of P21AD means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 1 | Area: fuel and air metering. |
| AD | The exact fault in that area. |
What to do next
- Note P21AD 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 P21AD
What does P21AD mean?
P21AD means "Reductant Level Sensor C Circuit". P21AD covers the electrical circuit of the third reductant level sensor, so it only exists on tanks with at least three level points. It is a generic code, so it means the same on every make.
Is it safe to drive with P21AD?
Drive gently and only to a workshop. With P21AD the car can go into limp mode (reduced power) to protect itself.
Will P21AD fail an emissions test?
Yes, it can. P21AD 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 P21AD to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P21AD clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.