Faulty Aftertreatment Diesel Exhaust Fluid Quality
The system has detected poor quality or contamination in 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 computer checks the DEF for quality. If it’s not good, like too diluted or full of impurities, it triggers this code.
What the computer is actually seeing
The Engine Control Module (ECM) monitors the quality of the DEF via a sensor. It expects a certain level of urea concentration, typically around 32.5% for proper operation. If the level drops below this threshold, it records SPN 587.
What a healthy reading looks like
DEF should have a urea concentration of 32.5% with a freezing point of -11°C (12°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.
- 11. Start with a visual inspection of the DEF tank and lines. Look for any leaks or signs of contamination. Decision: If leaks or contamination are found, address those issues first.
- 22. Check the DEF quality sensor connections for corrosion or loose fittings. Decision: Repair any bad connections found.
- 33. Test the DEF quality using a refractometer or a DEF quality tester. Decision: If the DEF is below 30% urea concentration or contaminated, replace the DEF.
- 44. Clear the code after taking these actions and perform a test drive. Decision: If the code returns and the DEF is good, suspect a faulty DEF quality sensor.
Common causes
- Contaminated or diluted DEF
- Faulty DEF quality sensor
- Incorrect DEF type used (e.g., agricultural grade instead of automotive)
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It is not recommended to drive long distances with this code, as it may lead to reduced engine performance and emissions compliance issues.
Will this code come back after I clear it?
If the underlying issue isn't fixed, yes, the code will likely return.
What happens if I use the wrong DEF?
Using the wrong DEF can result in sensor faults, system damage, and can cause vehicle restrictions.
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