P2DE8Cold Start Engine Coolant Bypass Valve D Stuck Open
- 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
- P2DE8 is GM's cold-start variant of P26C0 for valve D, the block rotary valve that sits between two mechanical end stops and meters coolant through the engine block. In the 2025 ECM tables (25OBDG03B) a failure counts when requested and measured position differ by more than 5° while the raw feedback is above 50°, i.e. on the open side; 4 of 5 seconds give a Type B fault, MIL on the second trip. Unlike P26C0 it only runs in low-flow coolant mode with catalyst warm-up active. Further conditions: at least 11 V, command between −5° and 115° and steady within 5° for 3 s, block coolant above −34 °C, and no calibration run in the last 37 s. An open block valve lets the block lose heat during warm-up, which delays catalyst light-off. The closed-side counterpart is P2E81.
- What you may notice
- Check engine light on after two trips
- Slow warm-up, weak cabin heating in cold weather
- Possibly higher fuel consumption on short trips
- Likely causes
- LikelyBlock rotary valve sticking in an open position (deposits, wear)
- PossibleValve actuator unable to drive the valve to the closed side
- PossibleChafed or corroded engine harness to the valve
- RareEnd-stop learn values implausible after repair or power loss
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €150 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.