P0E79 code meaning
Coolant Bypass Valve A Control Stuck/Open
Powertrain system Generic code P0Exx codes Check engine light
What P0E79 means
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.
P0E79 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor1 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of P0E79
- Weak cabin heat in electric mode
- Engine starts more often to supply heat
- Check engine light
Common causes of P0E79
- Most likelyValve A jammed open by debris or a broken internal part
- PossibleActuator no longer moves the valve
- Less likelyHoses swapped at the valve after a repair
- Less likelySkewed coolant temperature sensor misleading the check
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Coolant bypass valve aCooling system
What each part of P0E79 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 79 | The exact fault in that area. |
What to do next
- Note P0E79 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0E79
What does P0E79 mean?
P0E79 means "Coolant Bypass Valve A Control Stuck/Open". P0E79 reports that bypass valve A apparently remains open although the module has asked it to close. It is a generic code, so it means the same on every make.
Is it safe to drive with P0E79?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0E79 fail an emissions test?
Yes, it can. P0E79 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0E79 to fix?
Difficulty: medium. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will P0E79 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.