Powertrain, generic (extended)

P26C0 Engine Coolant Bypass Valve D Stuck/Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

GM uses P26C0 for the block rotary valve, which controls coolant flow through the engine block between two mechanical end stops; its tables label it as the engine block coolant valve stuck open. The ECM counts a failure when requested and measured position differ by at least 10° while the raw feedback sits at 50° or more, i.e. on the open side. The 2019 L3B table grades it Type A, one trip; the 2025 table 25OBDG03B lowers the gap to 5° and grades it Type B. The check is suspended during the valve's calibration run and needs at least 11 V. GM bulletin 21-NA-149 lists P26C0 among codes caused by a chafed engine harness on 2019–2021 trucks. An open block valve lets the block stay cooler than intended, slowing warm-up.

Likely causes

Block valve jammed on the open side
Chafed engine harness disturbing drive or feedback (GM 21-NA-149)
Position feedback reporting a wrong angle

Symptoms

  • Check engine light
  • Longer warm-up, especially in cold weather
  • 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 dthermostat housing

Related codes

P26C1P26C2P26BDP26BAP0128

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.