DEF Quality Fault
The engine control module detected a problem with the DEF quality.
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 is not getting the right quality of diesel exhaust fluid (DEF), which is crucial for reducing emissions. If it detects poor fluid quality, it can limit engine power or even prevent starting until it’s resolved.
What the computer is actually seeing
The ECM monitors DEF quality by checking conductivity and urea concentration. It expects specific conductivity values (around 1100 - 1500 microsiemens). If the readings are out of range, it triggers this fault.
What a healthy reading looks like
Conductivity should be around 1100 - 1500 microsiemens, urea concentration near 32.5%.
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 DEF fluid level in the tank; it should be at least half full. If low, refill with quality DEF and clear codes.
- 2Inspect DEF fluid for contamination. Look for discoloration or particles; if found, drain and flush the system.
- 3Verify the wiring and connectors for the DEF quality sensor. Look for fraying or corrosion that could cause poor connections.
- 4Using a scan tool, check the actual conductivity values reported by the DEF quality sensor; compare with expected values.
- 5If readings are outside normal, replace the DEF quality sensor and retest the system.
Common causes
- Poor quality or contaminated DEF fluid
- DEF tank contamination
- Faulty DEF quality sensor
- Wiring issues to the DEF quality sensor
- ECM calibration error
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
No, do not drive the vehicle as it can enter limp mode or refuse to start due to emissions control issues.
Will this code come back after I fix it?
If the underlying issue is resolved and all connections are secure, this code should not reappear.
Why does this code pair with SPN 6818?
SPN 6818 relates to DEF quality sensor voltage failures, which can occur alongside quality issues, indicating broader problems in the DEF system.
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