Powertrain, generic

P0E77 Coolant Bypass Valve A Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P0E77 is logged when valve A's drive line carries more voltage than the driver should allow, typically because the wire has rubbed through against a 12 V feed. A low-side driver then sees battery voltage while it is trying to pull the line down and usually reports overcurrent; with some designs an open line can float high and end up here too. In either case the valve no longer follows commands reliably. No manufacturer documents P0E77 publicly. Ford's 2019 hybrid summary handles the same situation on its bypass valve as P2683, again set after more than 5 seconds of driver fault status. CARB expects such outputs to be checked for circuit faults. A grounded line is P0E76 and an interrupted one P0E75; replacing the valve without checking the harness first rarely helps.

Likely causes

Control wire shorted to a battery or ignition feed
Open circuit that the driver interprets as high
Faulty valve A actuator electronics

Symptoms

  • Check engine light
  • Cabin heat unstable or missing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–450
Time0.5–2.5 h

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

Parts involved

coolant bypass valve awiring harness

Related codes

P0E75P0E76P0E78P0E7DP2683

References: fordservicecontent.com, law.cornell.edu.