Exhaust Pressure Control Valve Position Sensor Circuit Low (Generic)
The P4079 code means the vehicle's onboard diagnostic system has detected: Exhaust Pressure Control Valve Position Sensor Circuit Low (Generic). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $100 - $400 (parts and labor)
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Common Symptoms
- Check Engine Light on
- Valve position reading too low
- Exhaust pressure control compromised
- Possible EGR flow issues
Probable Causes (Ranked by Likelihood)
- Short to ground in sensor circuit Very High
- Sensor reading low due to failure High
- Corroded connector Moderate
- Valve physically stuck open Low
Step-by-Step Diagnostic Procedure
-
Test sensor voltage output across valve travel range
-
Check for shorts to ground
-
Inspect connector for corrosion
-
Verify valve moves freely through full range
Frequently Asked Questions
Can a stuck valve cause P4079?
Yes, if the valve is physically stuck open, the position sensor will correctly read low.
Can I drive with P4079?
You can drive short distances. The exhaust pressure control system is compromised but not dangerous.
How do I tell if it is the sensor or the valve?
Manually move the valve while watching the sensor output. If the sensor tracks the movement, the valve is the issue.
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