P0E79Coolant Bypass Valve A Control Stuck/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P0E79 reports that bypass valve A apparently remains open although the module has asked it to close. The control unit cannot see the valve directly; it infers the position from temperatures, typically by comparing two coolant sensors that should drift apart when the loops are separated. No manufacturer documents P0E79 publicly. Ford's 2019 hybrid summary describes exactly this logic for its older code P26AB, a valve stuck in the combined loop: if the heater-loop sensor reads more than 5 °F above the engine sensor within 60 seconds after a circuit fault, the valve is taken as stuck. An open valve lets heat escape into the larger loop, so cabin heat in electric mode suffers and the engine may warm up differently. CARB requires functional monitoring of such outputs. The opposite case is P0E7A.
- What you may notice
- Weak cabin heat in electric mode
- Engine starts more often to supply heat
- Check engine light
- Likely causes
- LikelyValve A jammed open by debris or a broken internal part
- PossibleActuator no longer moves the valve
- RareHoses swapped at the valve after a repair
- RareSkewed coolant temperature sensor misleading the check
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €150 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.