P0400Gmc SierraYears: 1996 - 2026
Exhaust Gas Recirculation (EGR) Flow Malfunction
Reviewed by ASE Certified Technician
What does this mean?
Code P0400 indicates the EGR system flow is not within the expected parameters. The EGR system recirculates exhaust gases back into the intake to reduce NOx emissions.
Disclaimer: This diagnostic code is part of the standard OBD2 system and can apply to Gmc Sierra models manufactured from 1996 to 2026. However, please note that the presence of this specific code depends on your vehicle's exact engine configuration, options, and production year.
Advertisement (In-Article)
Common Causes
Stuck or faulty EGR valve
Clogged EGR passages
Damaged, chafed, or broken wiring harness
Vacuum leak in intake system
PCM/ECM software needs update (TSB)
Symptoms to Watch For
- Check Engine Light is illuminated
- Rough or unstable idle
- Engine knocking or detonation noise
- Failed emissions test
- Significant loss of engine power
- Engine stalling or dying unexpectedly