Exhaust Gas Recirculation Sensor A Circuit Low
The DURAMAX-P0405 (Duramax) diesel fault code means: Exhaust Gas Recirculation Sensor A Circuit Low. This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- intermediate
- Estimated cost
- $400-$900
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Common Symptoms
- Reduced engine power / limp mode
- Check Engine Light
- Poor throttle response
- Possible DPF regen occurring more often (if DPF-related)
Probable Causes (Ranked by Likelihood)
- EGR position sensor low voltage / short to ground Very Likely
- Carbon / soot accumulation in EGR system (chronic Duramax issue) Likely
- Damaged EGR cooler — coolant leak into intake (LLY) Possible
- Wiring or connector fault to sensor/actuator Possible
Step-by-Step Diagnostic Procedure
Connect scan tool and check EGR commanded vs. actual position in live data
Command EGR open/closed with bidirectional scanner and verify smooth operation
Remove EGR valve and visually inspect for carbon packing — clean or replace as needed
If EGR cooler is suspect, pressure test for internal leaks (coolant getting into intake)
After cleaning, clear code and monitor for return — if returns, consider a replacement EGR valve
Frequently Asked Questions
What is P0405 on a Duramax?
Duramax code P0405 (Exhaust Gas Recirculation Sensor A Circuit Low) is a moderate-severity diagnostic trouble code triggered by the engine control module when it detects a problem in the associated system. Duramax EGR systems carbon up quickly — many owners install an EGR cleaning schedule every 75K miles.
Is a Duramax P0405 safe to drive?
Short-term driving is acceptable, but prolonged limp-mode operation indicates the EGR or DPF system needs service to prevent DPF damage.
How much does it cost to fix P0405 on a Duramax?
Typical repair runs $400-$900 depending on whether the valve can be cleaned or requires replacement.
P0405 on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown: