P21AB code meaning
Reductant Level Sensor B Circuit High
Powertrain system Generic code P21xx codes Check engine light
What P21AB means
P21AB is the high-side counterpart: GM sets it when level sensor 2 shows an open load (between 3.56 and 4.74 V, read 1.5 ms after the test pulse) or a short to battery voltage (above 4.74 V), each for more than 3 s, as Type A on the 6.6L LML and the 2014 Cruze diesel. GM's preliminary bulletin PIP4887B for 2010–2011 Silverado, Sierra, Express and Savana with the LML or LGH engine names P21AB together with P203D and P21B0 and the message Service Exhaust Fluid System: inspect wiring, connectors and terminal tension also when the faults are merely stored, and replace the DEF tank only when the wiring is sound. For the 2011 model year GM sorted P21AB into its tamper-related group.
P21AB 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 P21AB
- Check engine light on at once
- Service Exhaust Fluid System message
- Several level sensor codes stored together
Common causes of P21AB
- Most likelyOpen signal wire or spread terminal at the tank connector
- PossibleSignal wire shorted to a voltage source
- PossibleLevel sensor B open inside the tank assembly
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 P21AB 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. |
| AB | The exact fault in that area. |
What to do next
- Note P21AB 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 P21AB
What does P21AB mean?
P21AB means "Reductant Level Sensor B Circuit High". P21AB is the high-side counterpart: GM sets it when level sensor 2 shows an open load (between 3.56 and 4.74 V, read 1.5 ms after the test pulse) or a short to battery voltage (above 4.74 V), each for more than 3 s, as Type A on the 6.6L LML and the 2014 Cruze diesel. It is a generic code, so it means the same on every make.
Is it safe to drive with P21AB?
Drive gently and only to a workshop. With P21AB the car can go into limp mode (reduced power) to protect itself.
Will P21AB fail an emissions test?
Yes, it can. P21AB 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 P21AB to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P21AB clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.