SCR Inlet NOx Sensor Circuit Fault
The SCR inlet NOx sensor is malfunctioning or has a circuit issue.
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What it means (plain English)
The SCR inlet NOx sensor measures nitrogen oxides in the exhaust to help the engine manage emissions. A fault here means it can't provide accurate data, affecting emissions control.
What the computer is actually seeing
The engine control module (ECM) expects a voltage signal from the NOx sensor that varies between 0.2V to 4.5V depending on NOx concentration. If it sees a constant voltage or no signal, a fault is flagged.
What a healthy reading looks like
Normal NOx sensor voltage should be between 0.2V to 4.5V; typical operational range would show fluctuations based on exhaust composition.
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. Inspect the wiring and connector for the SCR inlet NOx sensor for any damage or corrosion. Are there any visible issues? If yes, repair/replace as necessary and retest.
- 22. Measure the voltage at the NOx sensor connector with the engine running. Is the voltage within the expected 0.2V to 4.5V range? If no, proceed to step 3. If yes, consider the sensor faulty and replace it.
- 33. Disconnect the NOx sensor and test the wiring back to the ECM for continuity using a multimeter. Is there continuity? If yes, replace the NOx sensor. If no, repair the wiring and retest.
Common causes
- Wiring issue in the NOx sensor circuit
- Faulty SCR inlet NOx sensor
- Corrosion or poor connection at the sensor connector
- Exhaust leaks near the sensor
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 lead to increased emissions and possible regulatory issues; however, it may still be drivable.
Will this fault code come back after I clear it?
If the underlying issue isn't resolved, yes, the code will likely return.
Why does this code often pair with SPN 5118?
Both codes relate to NOx sensor performance issues; addressing one may clear or highlight the other.
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