Reductant Quality Issue
The engine control module has detected a problem with the quality of the diesel exhaust fluid (DEF).
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 vehicle's computer is saying the DEF is either too diluted or contaminated, meaning it's not working properly to reduce emissions.
What the computer is actually seeing
The ECM expects the DEF to meet specific quality standards, typically calculated based on the fluid's urea concentration, which should be around 32.5%. If diluted, it's below that. If faulty, the sensor readings fluctuate outside of established thresholds.
What a healthy reading looks like
DEF should have a urea concentration of 32.5% +/- 1%. The temperature of the DEF should be above freezing (0°C or 32°F) during operation.
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.
- 1Check the DEF level in the tank. If low, refill with appropriate DEF. Decision: If level is good, proceed to next step.
- 2Inspect the DEF quality sensor wiring and connectors for signs of damage or corrosion. Decision: If damaged, repair/replace as needed and retest. If no issues, go to next step.
- 3Test the DEF fluid quality using a refractometer. Ensure it reads at 32.5% urea concentration. Decision: If bad, replace with fresh, quality DEF. If good, proceed to next step.
- 4Check the DEF quality sensor with a scan tool for proper operation and voltage (should be around 0.5-4.5V depending on quality). Decision: If out of range, replace sensor and retest.
Common causes
- Contaminated or diluted diesel exhaust fluid
- Faulty DEF quality sensor
- Wiring or connector issues in the DEF system
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's advisable to fix it soon, as it can affect emissions and lead to reduced performance.
Will this code come back after clearing?
If the underlying issue isn't fixed, yes, it will likely return.
Why does this code pair with P20B9?
Both codes are related to DEF quality issues and indicate problems with the same system.
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