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Home / DTC / P0EC6 — A/C Power Supply Relay Control Circuit/Open

P0EC6 — A/C Power Supply Relay Control Circuit/Open

Detailed page for trouble code P0EC6.

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Code

P0EC6

Generic P — Powertrain

A/C Power Supply Relay Control Circuit/Open

Brand: Generic
Type: P — Powertrain
Views: UK: 10 EN: 20 RU: 13
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Page language: EN

Causes

  • Blown A/C fuse or fusible link in the relay supply
  • Open or corroded wiring to the A/C power supply relay coil or control pin
  • Faulty A/C power supply relay (coil or contacts open)
  • Poor ground at relay or controller
  • Faulty ECM/BCM/climate control module driver output
  • Intermittent connector or terminal contact (corrosion, bent pins)

Symptoms

  • A/C compressor will not engage
  • No air conditioning or minimal cooling
  • A/C clutch/relay not clicking when A/C requested
  • DTC P0EC6 stored and possibly related A/C codes
  • Possible MIL illumination depending on vehicle

What to check

  • Read freeze frame and live data with a scan tool to confirm conditions when code set
  • Visually inspect relay, fuse, relay socket and related wiring for damage or corrosion
  • Check battery voltage and charging system health (low voltage can affect circuits)
  • Verify A/C relay clicks when A/C is commanded (listen/feel at relay)
  • Measure voltage at relay supply terminal and at relay control terminal with A/C ON
  • Inspect and wiggle connectors while monitoring live data to reproduce code or loss of control

Signal parameters

  • Relay supply (B+) at relay battery input: ~12 V (vehicle off) to ~13–14.5 V (engine running)
  • Relay coil/control input when commanded: switched to ground or +12 V depending on design (use wiring diagram). Expected to change state when A/C is commanded
  • Typical relay coil resistance: ~70–200 ohms (varies by relay type) — measure and compare to specification
  • Control driver current: generally low (tens to a few hundred mA); module should be able to switch coil current
  • Compressor clutch feed when relay closed: near battery voltage (within ~1 V)

Diagnostic algorithm

  1. Retrieve freeze frame and full set of stored codes. Note ignition key position and A/C request conditions when code set.
  2. Visually inspect A/C relay, fuse(s), relay socket and harness for obvious damage, corrosion, or a blown fuse. Replace blown fuse(s) as needed and retest.
  3. With a scan tool, command A/C clutch/relay ON while monitoring relay operation. If relay does not click, proceed.
  4. Measure battery voltage at relay supply terminal. Then measure voltage at relay control terminal while A/C is commanded. If there is no change at control terminal, suspect open control circuit or driver.
  5. Check continuity between the relay control terminal and the controlling module pin with ignition OFF (ignore if manufacturer requires powering module off). Repair any open circuits. Do not short any pins; use a low-voltage continuity tester or DMM.
  6. Check module ground(s) related to the relay control circuit for low resistance to chassis ground. Clean or repair poor grounds.
  7. Swap the suspect relay with a known-good relay of the same type (if available) and recheck operation. If swapping fixes the issue, replace relay.
  8. If control wire is present but relay still not energized, back-probe module output while commanding A/C to confirm driver output (active low or high per wiring diagram). If module does not switch, test the module output per manufacturer procedure.
  9. Repair wiring harness faults (broken wires, corroded connectors, poor pin contact) and secure harness away from heat or rubbing points. Replace relay or module as required.
  10. Clear codes, perform A/C operation test in different conditions, and verify the code does not return. Road test or run the vehicle to confirm proper A/C function.

Likely causes

  • Failed A/C relay (most common)
  • Blown inline fuse or fusible link feeding the relay coil or relay supply
  • Open control wire from ECM/BCM to relay coil (broken wire, pin pushed out)
  • Poor chassis or module ground at relay or control module
  • Connector corrosion or water intrusion at relay socket

Fault status

⚠️ Status
A/C power supply relay control circuit open — control module detects no valid control signal to the A/C relay (relay coil not being energized).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5 - 2.5 hours

Similar codes

P0EC5 P0EC7 P0627 P0562
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