P0EC8: A/C Power Supply Relay Control Circuit High

What it means

The A/C power supply relay control circuit voltage is higher than expected. The module sets this code when it detects high voltage in the monitored relay control circuit.

How it works

The A/C power supply relay routes electrical power to the air-conditioning system, and its control circuit carries the module's command and feedback. P0EC8 sets when that circuit reads higher than expected, such as when relay wiring is shorted to voltage or the relay or module driver is not switching correctly.

Common causes

Most likely first.

1. Short to voltage in relay wiring
2. Faulty A/C relay
3. Loose or corroded connector
4. Failed control module driver

Symptoms

• A/C may not operate
• A/C warning light
• Hybrid or EV warning light

How to diagnose it

1. Save freeze-frame data and review A/C relay command and control-circuit live data to identify when the high reading appears.
2. Inspect the A/C relay and its connector for corrosion, loose terminals, damaged insulation, or wiring contacting a power feed.
3. Check the relay and control wiring for a short to voltage, following the vehicle's wiring diagram and manufacturer procedure.
4. Test relay operation and the relevant control-circuit connections against the manufacturer's specification.
5. If the relay and wiring check out, verify the module driver output using the manufacturer's diagnostic procedure.

Common fixes

• Secure or clean a loose or corroded relay connector.
• Repair wiring shorted to a voltage feed.
• Replace a faulty A/C relay.
• Repair or replace a failed module driver after confirming the circuit is sound.

Can I keep driving?

If only A/C operation is affected, you may be able to drive, but cooling and window defogging may be unavailable. If a hybrid or EV warning or reduced-power condition occurs, stop safely and follow the vehicle's instructions.