P26A8 Engine Coolant Bypass Valve A Position Sensor Circuit Intermittent/Erratic

P26A8 targets a feedback signal that jumps or drops out briefly instead of staying wrong. No manufacturer publishes a definition for this exact code. The closest documented logic is in GM's 2011 Volt table, where under P26A9 the controller flags a reading that changes by more than 6 % between samples ten steps apart (8 of 10 or 80 of 100 samples) although no movement was commanded. Subaru's bulletin 09-80-21 lists P26A-series codes as consequences of moisture reaching the sensor of the thermo control valve on 2019–2021 models. CARB asks for rationality checks on inputs that affect emissions. In practice a loose terminal, a cracked solder joint or a worn sensor track causes it, often only with vibration or heat.

Likely causes

Symptoms

• Check engine light that may come and go
• Erratic heater output or engine temperature
• Code returns after clearing, often on rough roads

Repair estimate

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

Parts involved

Related codes

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