NOx Sensor Circuit Bank 1 Low Input (Generic)
The P4026 code means the vehicle's onboard diagnostic system has detected: NOx Sensor Circuit Bank 1 Low Input (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
- NOx reading unusually low
- SCR system may over-inject DEF
- DEF consumption increased
- Possible inducement timer active
Probable Causes (Ranked by Likelihood)
- NOx sensor reading low due to contamination Very High
- Faulty NOx sensor module High
- Wiring issue causing low signal Moderate
- SCR catalyst over-performing masking issue Low
Step-by-Step Diagnostic Procedure
-
Check NOx sensor readings at idle and under load
-
Inspect sensor connector and wiring
-
Verify DEF injection rate is correct
-
Test NOx sensor with diagnostic scan tool
Frequently Asked Questions
What happens if the NOx sensor reads too low?
The SCR system may inject too much DEF because it thinks more NOx reduction is needed. This wastes DEF and can cause DEF crystallization in the exhaust system.
Can I drive with P4026?
You can drive short distances but the DEF system warning may escalate. On some vehicles, a countdown timer will start limiting speed if the issue is not resolved.
Is P4026 covered by emissions warranty?
On many diesel vehicles, the NOx sensor is covered under the federal emissions warranty for 5 years or 50,000 miles. Check with your dealer.
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