Powertrain, generic (extended)

P26BB Engine Coolant Bypass Valve C Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P26BB is GM's main functional code for its rotary coolant flow control valve. The ECM compares commanded and measured angle; a gap above 12° after the target has settled, or movement slower than calibrated, counts as a fault. In the 2019 L3B table this is Type A (4 of 5 s), in the 2025 diesel table Type B (8 of 10 s). Several GM bulletins concern it: 21-NA-256 (2019–2022 engines LSY, L3B, L3T) blames a break-in phase of the valve under about 2,000 miles and calls for a new valve only on repeat; 20-NA-100 (2.7L L3B pickups 2019–2020) and 22-NA-082 (3.0L diesel 2020–2022) prescribe new ECM software; PIE0697 gathered field data on the diesel with P2B60. A sluggish valve can let the engine run too warm or too cool.

Likely causes

New valve still in its break-in phase (GM, low mileage)
ECM calibration needing an update per GM bulletin
Valve or actuator sticking or worn
Inaccurate valve position feedback

Symptoms

  • Check engine light
  • Coolant temperature higher or lower than normal
  • Code may disappear after further driving on a new valve

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–900
Time0.4–4 h

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

Parts involved

coolant bypass valve cthermostat housing

Related codes

P26BAP26BCP26B7P23C4P23C5P2B60

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