Powertrain, generic (extended)

P26A4 Engine Coolant Bypass Valve A Position Sensor Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

Many electric coolant valves carry a potentiometer or Hall element that reports the actual valve angle back to the controller. P26A4 is the general circuit code for that feedback on valve A: the signal is missing or cannot be assigned to a more specific low, high or erratic fault. No manufacturer documents P26A4 itself in public. GM's Volt tables cover the same sensor only through P26A6/P26A7, and Subaru bulletin 09-80-21 (Forester, Outback, Legacy, Crosstrek 2019–2021) mentions P26A-series codes in general when water reaches the sensor portion of the thermo control valve. CARB requires input signals to be checked for continuity. Without valid feedback the controller loses track of the valve, so warm-up and cooling may run on a fallback setting.

Likely causes

Moisture or corrosion inside the valve's position sensor section
Loose, corroded or damaged connector or feedback wiring
Missing 5 V reference or ground for the position sensor

Symptoms

  • Check engine light
  • Slow warm-up or weak cabin heat
  • Possible additional valve or coolant temperature codes

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–900
Time0.5–4 h

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

Parts involved

coolant bypass valve aposition sensorwiring harness

Related codes

P26A5P26A6P26A7P26A8P2681

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