Aftertreatment Diesel Exhaust Fluid Quality Fault
Indicates a fault 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 truck's computer is detecting that the diesel exhaust fluid isn't up to standard, which can affect emissions control and performance.
What the computer is actually seeing
The computer reads signals from the DEF quality sensor. If the sensor measures fluid conductivity, temperature, or concentration outside the expected range, it triggers the code.
What a healthy reading looks like
DEF should have a urea concentration of 32.5% at a temperature between 10°C to 30°C (50°F to 86°F).
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 tank level and quality. Make sure it meets EPA standards for purity.
- 2Inspect wiring and connectors around the DEF quality sensor for damage or corrosion.
- 3Test the DEF quality sensor using a scan tool to see if it is outputting valid data (check against expected values).
- 4If DEF fluid is contaminated or incorrect, replace it with fresh, certified DEF and clear the code. If the code returns, consider replacing the sensor.
Common causes
- Bad diesel exhaust fluid (impure or incorrect formulation)
- DEF quality sensor failure
- Wiring issue to the DEF quality sensor
- Incorrect DEF nozzle or tank contamination
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's best to fix it soon, as poor DEF quality can affect emissions controls and lead to reduced performance.
Will this code come back after clearing it?
If the underlying issue is not resolved, such as a bad sensor or contaminated DEF, it will likely return.
Why did my truck go into limp mode after this code?
The system limits performance to protect the engine and emissions controls when it detects a DEF quality issue.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
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