Powertrain, generic (extended)

P26AA Engine Coolant Bypass Valve A Position Sensor Maximum Stop Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P26AA is the upper-limit partner of P26A9: the controller cannot confirm or learn the maximum end stop of valve A, or the reported value at full travel lies outside the expected window. No manufacturer publishes criteria for this code. GM's Volt logic for P26A9 shows how such checks work: the valve is driven to an end, given a fixed time to arrive and relearned several times before a fault is stored. Subaru's bulletin 09-80-21 names the P26A family in general for sensor corrosion on its thermo control valve. CARB expects the OBD system to notice when such an output ignores its commands, wherever a test of its response is feasible. Likely causes are mechanical binding near full open, a damaged stop, or a sensor that saturates early.

Likely causes

Valve binding before reaching its maximum position
Worn or broken mechanical end stop or gear
Position sensor out of calibration near its upper end

Symptoms

  • Check engine light
  • Reduced cooling under high load
  • Heater or engine temperature not as expected

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€0–900
Time0.3–4 h

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

Parts involved

coolant bypass valve aposition sensor

Related codes

P26A9P26A5P26A3P26AB

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.