Reductant System Performance Problem
The reductant system is not functioning correctly, affecting emissions.
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What it means (plain English)
The engine control module noticed that the diesel exhaust fluid (DEF) system isn't working right, meaning it may not be treating emissions properly. This can cause higher pollution levels.
What the computer is actually seeing
The engine control module (ECM) evaluates the performance of the reductant system based on feedback from various sensors, such as temperature and level sensors, as well as the NOx sensors downstream. It looks for an expected reduction in NOx emissions post-treatment but notes that the expected results aren't achieved.
What a healthy reading looks like
Temperature of DEF: between 32°F (0°C) and 122°F (50°C). DEF level should be above 25% for proper operation. NOx levels should be within manufacturer's specifications, typically under 200 ppm after treatment.
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. Ensure level is above 25% and fluid is not frozen or contaminated. If it's low or contaminated, refill with fresh DEF or replace it.
- 22. Inspect the wiring and connectors to the DEF injector and NOx sensors for damage or corrosion. Repair as needed.
- 33. With the ignition on and engine off, use a scan tool to read live data from the NOx sensors. Confirm readings match expected values. If readings are outside range, replace the faulty NOx sensor.
- 44. Test the DEF injector operation. Command the injector to activate using a scan tool and confirm DEF is being injected. If not, replace the DEF injector.
- 55. If all components check out but the code persists, consider updating the ECM software to the latest version. Some codes can be resolved through software. Perform a reset after updates.
Common causes
- Low DEF level or concentration
- Faulty DEF injector
- Blocked DEF lines or nozzle
- Faulty NOx sensor
- ECM software issue
Typical repair cost
$$ - $$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not ideal to drive with this code as it can affect emissions compliance, but the vehicle may still be drivable unless limp mode activates.
Will this issue come back after clearing the code?
If the root cause isn't fixed, yes, the code will likely return after a short distance.
Why does this code pair with others?
This code is likely to show alongside others related to the NOx reduction system because they affect the same components and performance.
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