P2D1CCold Start EGR A/B Ratio Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2D1C belongs to engines with two exhaust gas recirculation paths, A and B, whose share of the total recirculated flow is scheduled differently right after a cold start. The code says that during the cold start strategy the split between both paths did not follow its target. CARB obliges diesels to verify EGR valve position and EGR cooler bypass while the cold start monitoring window applies (at least 6 h soak, ambient from -6.7 °C). GM's 2025 table for the 3.0 l LZ0 diesel shows the layout: EGR A is the high pressure loop (P0401), EGR B the low pressure loop (P049B), steered by a desired LP split; there the cold start HP valve is checked under P034F (tracking error over 10 %, Type B). No manufacturer documents P2D1C publicly. P04DD and P04DE judge EGR A flow alone; expect higher NOx after cold starts.
- What you may notice
- Check engine light after cold starts, often without noticeable driveability change
- Rough or smoky running in the first minutes after starting
- Further EGR flow codes such as P0401 or P049B stored alongside
- Likely causes
- LikelyEGR valve A or B sooted or sluggish, so it cannot reach its cold start position
- PossibleRestricted EGR cooler or leaking pipe in one of the two loops
- PossibleFaulty pressure, temperature or position signal used to estimate the flows
- RareEngine control software that misjudges the split in cold weather
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €1,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.