OBD Engine Coolant Bypass Valve B Stuck/Open
What it means
P26AF stands for Engine Coolant Bypass Valve B Stuck/Open. P26AF is a P code, so the fault sits in the engine, transmission and emissions systems. For P26AF, the second digit places it in computer output circuits. For P26AF, work through the cause list below, cheapest checks first.
Where it lives
For P26AF, the part to look at first is the valve named here.
What to check first
For P26AF, clear the code, drive a short distance and read it again, since a code that comes back is still there and one that does not was history.
Check these first
- P26AF: Faulty sensor or actuator in the control circuit
- P26AF: Wiring, connector, or fuse problem for the affected output
- P26AF: Low or unstable system voltage from the battery or charging system
- P26AF: Failed PCM/ECM or a software error
- P26AF: Poor ground connection for the control module
What to do next
P26AF is a fault in the computer output circuits system. The steps below are general, so what actually failed on your vehicle may not be what P26AF names.
- P26AF: Verify battery voltage and charging system health first
- P26AF: Read all related module codes with an OBD-II scanner
- P26AF: Inspect wiring, connectors, and grounds for the affected circuit
- P26AF: Test the sensor or actuator with live data and actuation commands
- P26AF: Check for PCM software updates or TSBs before replacing modules
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Updated
Generic SAE J2012 definition. Last updated 2026-08-30.