NOx Sensor Circuit Low
The NOx sensor's circuit is reading below normal levels.
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What it means (plain English)
The NOx sensor is tracking nitrogen oxide levels in the exhaust, and it's showing less voltage than it should, which indicates a potential problem. Normally, the sensor should read between 0.1 to 4.9 volts under different load conditions; if it's too low, it could mean a wiring issue or a bad sensor.
What the computer is actually seeing
The computer expects the NOx sensor to output a voltage signal that varies with the concentration of nitrogen oxides. A reading below 0.1 volts consistently indicates a fault in the circuit or the sensor itself.
What a healthy reading looks like
NOx sensor voltage should be between 0.1V (low NOx levels) and 4.9V (high NOx levels).
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 wiring and connectors to the NOx sensor for damage or corrosion. Ensure all connections are secure.
- 22. Measure the voltage at the NOx sensor connector: key on, engine off. You should see a voltage reading around 0V. If it's much lower, investigate the wiring.
- 33. Start the engine and let it run until operating temperature; check the NOx sensor voltage output. It should fluctuate between 0.1V and 4.9V. If it's still low, it's likely the sensor is bad.
- 44. If no faults found in wiring and the sensor output is still low, replace the NOx sensor and clear the fault code.
- 55. After replacement, verify the operation by running the engine and checking that the voltage returns to normal. If the issue persists, further investigate the engine control module.
Common causes
- Faulty NOx sensor
- Damaged wiring or connectors
- Open or short circuit in the NOx sensor circuit
- Contamination of the sensor
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not recommended to drive long distances as it can lead to emissions problems and might damage the catalyst.
Will this fault come back?
If the underlying issue isn't solved, yes, the code will likely return after clearing it.
Why might this code appear with SPN 3361?
Both codes are related to exhaust emissions control; a fault in the NOx sensor can trigger both codes.
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