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P0612Fuel Injector Control Module Relay Control

There is a fault in the circuit the engine computer uses to control the fuel injector control module's power relay.

Definition

On engines with a separate injector driver module, the PCM controls a relay that supplies main power to that module and monitors the relay control circuit for opens, shorts, and correct feedback. P0612 sets when the commanded relay state and the monitored circuit disagree. If the relay fails to energize, the injector module gets no power and the engine will crank but not start; an intermittent circuit can cause sudden stalling. The MIL illuminates when the fault is detected.

Common causes

  • Failed injector control module power relay
  • Open, shorted, or chafed wiring in the relay control circuit
  • Corroded relay socket terminals or blown feed fuse
  • Poor connection at the PCM or injector driver module connectors
  • Faulty PCM relay driver (least common)

Common misdiagnoses

  • Replacing the injector driver module when its power relay or feed circuit is at fault
  • Replacing fuel injectors for a no-start caused by an unpowered driver module
  • Replacing the fuel pump for a crank/no-start that is actually an injector power issue
  • Condemning the PCM before testing the relay and its wiring

Troubleshooting steps

  1. 1.Test the relay itself

    Remove the relay and bench-test it: coil resistance typically 50-120 ohms, and the contacts should close with 12 V applied; swap with a known-good identical relay as a quick check.

  2. 2.Verify power and control at the relay socket

    Check for battery voltage on the relay feed terminals and confirm the PCM-side control terminal switches when the key is cycled.

  3. 3.Confirm the injector module receives power

    With the relay energized, verify battery voltage at the injector control module's main power input pin.

  4. 4.Inspect and test the control wiring

    Check the control wire from relay to PCM for continuity, short to ground, and short to power with connectors disconnected.

  5. 5.Wiggle-test for intermittents

    Monitor the circuit while flexing the harness and tapping the relay to reproduce stalling-type intermittent faults before releasing the vehicle.

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