NOx Sensor Circuit Bank 1 Range/Performance (Generic)
The P4025 code means the vehicle's onboard diagnostic system has detected: NOx Sensor Circuit Bank 1 Range/Performance (Generic). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $300 - $800 (parts and labor)
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Common Symptoms
- Check Engine Light on
- DEF system warning
- Reduced SCR efficiency
- Higher than normal DEF consumption
- Possible speed limitation countdown
Probable Causes (Ranked by Likelihood)
- Contaminated NOx sensor element Very High
- NOx sensor calibration drift High
- Exhaust leak near NOx sensor Moderate
- SCR catalyst degradation affecting readings Low
Step-by-Step Diagnostic Procedure
-
Check NOx sensor readings against expected values
-
Inspect for exhaust leaks near sensor location
-
Verify DEF quality and concentration
-
Compare pre-SCR and post-SCR NOx values
Frequently Asked Questions
Can bad DEF cause P4025?
Yes, contaminated or diluted DEF can cause the SCR system to not reduce NOx properly, which the NOx sensor will detect as a range or performance issue.
Can I drive with P4025?
You can drive short distances but a countdown timer may start. If the timer reaches zero, the vehicle will be limited to 5 mph until repaired.
How do I check DEF quality?
DEF should be 32.5% urea concentration. You can buy a DEF refractometer for about $30 to test it.
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