P21CE: Reductant Quality Module Performance

What does P21CE mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Check engine light on
• DEF system error message in the display
• Erratic DEF level reading

Common causes

• High Contaminated or degraded DEF disturbing the measurement
• Medium Quality module internally faulty
• Medium Crystals or air bubbles on the sensing element
• Low Poor contact at the module connector

Likelihood is a general estimate across vehicles; your make and model may differ.