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Home / DTC / P0EC7 — A/C Power Supply Relay Control Circuit Low

P0EC7 — A/C Power Supply Relay Control Circuit Low

Detailed page for trouble code P0EC7.

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Code

P0EC7

Generic P — Powertrain

A/C Power Supply Relay Control Circuit Low

Brand: Generic
Type: P — Powertrain
Views: UK: 12 EN: 15 RU: 13
AI status
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Page language: EN

Causes

  • Blown fuse for A/C power/relay circuit
  • Failed A/C power supply relay (stuck open or internal short)
  • Short to ground in the relay control wiring or connector
  • Open or high-resistance wiring between relay and ECM/PCM
  • Corroded or loose relay socket/connector pins
  • Faulty ECM/PCM driver transistor or internal circuit

Symptoms

  • A/C compressor/clutch will not engage or cycles unpredictably
  • Reduced or no cabin cooling
  • Possible A/C-related warning messages or MIL illumination
  • No relay click when A/C requested from controls

What to check

  • Retrieve freeze frame and live data with a scan tool; confirm A/C request and stored conditions
  • Visually inspect fuses and A/C relay for damage or corrosion
  • Locate A/C power supply relay and inspect socket/connector for corrosion, bent pins, or melted plastic
  • Backprobe relay control and supply pins with ignition and A/C request active; measure voltage
  • Check for continuity/short to ground on control wire with relay removed
  • Compare measured voltages to battery voltage and ground reference

Signal parameters

  • Ignition ON, A/C OFF: control pin typically at vehicle-specific inactive level (often ~0 V or battery voltage depending on circuit design)
  • A/C request ON (relay energized): control pin should change to the expected commanded level (commonly near battery voltage if relay coil is switched to battery, or pulled to ground if PCM grounds the coil). Refer to vehicle wiring diagram for exact expected polarity
  • Typical relay coil resistance: commonly 40–200 ohms (vehicle specific) — measure with relay removed
  • Short-to-ground fault condition: control circuit reads very low voltage (near 0 V) when it should be high during A/C request

Diagnostic algorithm

  1. Obtain full wiring diagram and connector pinouts for the A/C power supply relay and ECM/PCM driver
  2. Verify the code and note freeze-frame data and A/C request status using a scan tool
  3. Visually inspect relay, socket, fuse, and wiring for obvious damage or corrosion
  4. With ignition OFF, remove the A/C relay and inspect pins for corrosion, melting, or bent terminals; clean or repair as needed
  5. Measure coil resistance on the removed relay; if out of spec, replace relay
  6. With relay removed, ignition ON and A/C request active, backprobe the relay control and supply terminals: verify supply (battery) voltage on the feed terminal and expected control signal on the control terminal. If control terminal is low when it should be high, proceed
  7. If control terminal is low, disconnect the harness at the ECM/PCM and check continuity of the control wire to the relay socket and for short to ground. If short to ground exists between relay socket and ground, isolate and repair wiring
  8. If wiring checks OK, backprobe the ECM/PCM control pin with connector attached and command A/C ON; if the PCM is not producing the correct control signal, verify grounds/power to ECM and consult OEM guidance before replacing ECM
  9. After repair or component replacement, clear codes and perform functional test with scan tool and A/C system operation cycles to confirm the fault does not return
  10. If unsure or ECM suspected, consult OEM service information and consider professional electrical diagnostics

Likely causes

  • A/C relay stuck or internally shorted
  • Pin-to-pin short between relay control wire and ground (chafing, pinched harness)
  • Blown or intermittent fuse supplying relay/coils
  • Corroded relay socket or poor connector contact
  • PCM/ECM output driver failure (less common)

Fault status

⚠️ Status
A/C Power Supply Relay control circuit voltage is lower than expected when commanded. Possible short to ground, relay or wiring fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0EC6 P0627 P0562 P0563
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