Powertrain, generic (extended)

P26C2 Engine Coolant Bypass Valve D Stuck Closed

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P26C2 is the closed-side partner of P26C0, and GM again applies it to the block rotary valve of its engines. The test is the same comparison of commanded and actual angle, at least 10° apart in the 2019 L3B table (Type A, one trip) and 5° in the 2025 table 25OBDG03B (Type B), but here the raw feedback stays below 50°, so the valve is judged closed. The diagnostic is skipped while the end stops are being learned and when system voltage is under 11 V. GM bulletin 21-NA-149 includes P26C2 in its list of codes from a chafed engine harness. A block valve that stays shut stops coolant from circulating through the block, so local hot spots and engine overheating are the real risk; reduced power or a warning may follow.

Likely causes

Block valve seized on the closed side
Chafed engine harness (GM bulletin 21-NA-149)
Weak actuator motor unable to open the valve

Symptoms

  • Check engine light, immediately on GM 2019 L3B
  • Rising coolant temperature or overheat warning
  • Reduced engine power

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

P26C0P26C1P26BCP0217

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