P21CE code meaning
Reductant Quality Module Performance
Powertrain system Generic code P21xx codes Check engine light
What P21CE means
P21CE says the DEF quality module as a unit is not working properly: it is supplied and talking to the controller, but its self-test or the plausibility of its output fails, so the controller cannot rely on the concentration it reports. This differs from P206B to P206D, which grade the measured concentration, and from P21CD, which concerns the module supply. Nissan uses P21CE on the 2019 Titan XD with the Cummins 5.0 L V8, often with P1349 for an erratic tank level, and a DEF system message may appear. Bulletin NTB20-005 has the technician follow the normal diagnosis and, if it leads to part replacement, first drain the tank and refill it with fresh fluid, reinstalling the pump with a new seal. Ford's 2023 diesel summary reports an internal quality sensor error as P206B instead.
P21CE 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 P21CE
- Check engine light on
- DEF system error message in the display
- Erratic DEF level reading
Common causes of P21CE
- Most likelyContaminated or degraded DEF disturbing the measurement
- PossibleQuality module internally faulty
- PossibleCrystals or air bubbles on the sensing element
- Less likelyPoor contact at the module connector
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant quality sensor
What each part of P21CE 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. |
| CE | The exact fault in that area. |
What to do next
- Note P21CE 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 P21CE
What does P21CE mean?
P21CE means "Reductant Quality Module Performance". P21CE says the DEF quality module as a unit is not working properly: it is supplied and talking to the controller, but its self-test or the plausibility of its output fails, so the controller cannot rely on the concentration it reports. It is a generic code, so it means the same on every make.
Is it safe to drive with P21CE?
Drive gently and only to a workshop. With P21CE the car can go into limp mode (reduced power) to protect itself.
Will P21CE fail an emissions test?
Yes, it can. P21CE 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 P21CE to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P21CE clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.