Reductant Quality Performance
The engine control module detected a problem with the quality of the DEF fluid in the system.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The engine's computer checks the quality of the diesel exhaust fluid (DEF) to ensure it's not contaminated. If it finds something wrong, it throws this code.
What the computer is actually seeing
The engine control module monitors the quality of the DEF using measurements from the DEF quality sensor or by evaluating the DEF injection system's performance.
What a healthy reading looks like
DEF should have a urea concentration of 32.5%; measurements out of range may trigger this code.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check the DEF fluid level and quality; make sure it's fresh, with a 32.5% urea concentration.
- 22. Inspect the wiring and connectors between the DEF quality sensor and the ECM for any damage or corrosion.
- 33. If the fluid and connections are good, use a scan tool to check if the DEF quality sensor voltage and signals are within specified limits (typically around 0.5V to 4.5V depending on quality).
- 44. If the sensor is out of spec, replace it. If it's within spec, consider checking the DEF injector and system pressure.
Common causes
- Contaminated DEF fluid
- Faulty DEF quality sensor
- DEF heater malfunction
- Wiring issues to the sensor or module
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Not ideal. Vehicle may enter limp mode, so fix this soon.
Will this code come back after clearing it?
If the underlying issue isn't addressed, yes, it'll likely return.
Why does this code occur alongside P20E8?
P20E8 indicates specific emissions issues relating to DEF quality; they often occur together.
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