Powertrain, generic

P0EC8 A/C Power Supply Relay Control Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P0EC8 indicates that the relay control circuit for the A/C power supply carries too high a voltage, typically a short to a battery-fed wire. A low-side driver then pushes current straight into that short when it switches on; modern output stages detect the overcurrent, turn themselves off and log this code, so the relay stays open and the A/C components get no power. With a high-side driver the same fault can hold the relay on permanently. No manufacturer documents P0EC8 publicly. CARB explicitly lists shorts toward a higher voltage as a circuit fault that output component monitoring must catch. Look for wires rubbing on a powered conductor or a shorted coil. Low side: P0EC7; clutch relay analogue: P0647.

Likely causes

Control line shorted to a battery-fed wire
Relay coil with too low resistance overloading the driver
Incorrect relay type fitted

Symptoms

  • A/C has no power and stays off
  • Relay may stay energised permanently on high-side switched designs

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€20–350
Time0.5–2 h

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

Parts involved

ac power supply relayhvac control modulewiring harness

Related codes

P0EC6P0EC7P0647

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