Powertrain, generic (extended)

P2DE8 Cold Start Engine Coolant Bypass Valve D Stuck Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Block rotary valve sticking in an open position (deposits, wear)
Valve actuator unable to drive the valve to the closed side
Chafed or corroded engine harness to the valve
End-stop learn values implausible after repair or power loss

Symptoms

  • Check engine light on after two trips
  • Slow warm-up, weak cabin heating in cold weather
  • Possibly higher fuel consumption on short trips

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€150–900
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

coolant bypass valve d

Related codes

P2E81P26C0P26C2P2DE7P2DE9

References: gsi.ext.gm.com, law.cornell.edu.