Powertrain, generic

P0E78 Coolant Bypass Valve A Control Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P0E78 is the plausibility code for the actuator circuit of bypass valve A. Neither an open nor a short is present, yet current, feedback or response time of the actuator do not fit what the module has commanded: a coil whose resistance has drifted, a motor that labours against a sticky shaft, or a supply that sags under load. For motor-driven valves with position feedback the module may also see the valve arrive late or stop short. No manufacturer documents P0E78 publicly. Ford's hybrid summary for 2019 shows the general idea of checking the actual valve position once an electrical problem is known, under P26AB. CARB asks for functional checks of output components in addition to circuit tests. Hard electrical faults are P0E75 to P0E77; a valve that stays put is P0E79 or P0E7A.

Likely causes

Deposits or wear making the valve A mechanism sluggish
High resistance at connector or ground of the valve circuit
Low supply voltage to the actuator under load

Symptoms

  • Check engine light
  • Heating output varies from trip to trip

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–550
Time0.5–3 h

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

Parts involved

coolant bypass valve awiring harness

Related codes

P0E75P0E76P0E77P0E79P0E7AP0E7E

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