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P codepowertrainMedium severity

P0079Exhaust Valve Control Solenoid Circuit Low (Bank 1)

The Bank 1 exhaust valve control solenoid circuit is reading lower voltage than expected, typically from a short to ground or an open circuit.

Definition

P0079 sets when the PCM detects voltage on the Bank 1 exhaust valve control solenoid circuit below the expected threshold, indicating a short to ground, open wiring, or a failed solenoid coil. The PCM illuminates the MIL and defaults the exhaust valve control system to its base position, which can reduce power and fuel economy and raise emissions until the circuit fault is repaired.

Common causes

  • Solenoid control or feed wire shorted to ground
  • Open circuit from broken wiring or a failed connector terminal
  • Open or internally shorted solenoid winding
  • Corrosion from water intrusion at the connector
  • Harness chafed through at a bracket or the valve cover edge
  • Failed PCM driver holding the circuit low

Common misdiagnoses

  • Replacing the solenoid when a grounded harness is the cause
  • Replacing the PCM before isolating the short
  • Treating the code as a mechanical VVT or oil pressure problem
  • Replacing the exhaust cam sensor, which does not share this circuit

Troubleshooting steps

  1. 1.Measure winding resistance

    Check the Bank 1 exhaust solenoid coil against spec; near-zero ohms means a shorted coil, infinite means an open coil.

  2. 2.Test for short to ground

    With both ends of the circuit disconnected, verify no continuity between each circuit wire and chassis ground.

  3. 3.Confirm supply voltage

    Key on, verify battery voltage on the feed terminal at the solenoid connector; absence points to a blown fuse or open feed wire.

  4. 4.Inspect harness routing

    Look for rub-through points where insulation is worn to bare copper against metal, especially near engine mounts and harness clips.

  5. 5.Verify PCM switching

    Scope or test-light the control wire while commanding the solenoid; correct switching with a good coil and wiring clears the PCM as a suspect.

  6. 6.Repair, clear, and retest

    Fix the identified fault, clear the DTC, and confirm normal exhaust valve control response on a warm-engine road test.

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