Engine

P0079 — Exhaust Valve Control Solenoid Circuit Low (Bank 1)

Severity: medium Drive with care, to a shop

What P0079 means

The engine control module drives a solenoid that adjusts exhaust valve operation or exhaust cam timing in variable valve timing systems. P0079 sets when the voltage in the Bank 1 solenoid circuit is lower than expected. The cause may be the solenoid itself, a short to ground in the wiring, or a poor connection.

Symptoms

  • Check Engine light on
  • Rough or unstable idle
  • Reduced engine power
  • Worse fuel economy
  • Hesitation when accelerating

Possible causes

  1. Faulty exhaust valve control solenoid
  2. Open or shorted wiring or connector
  3. Signal wire shorted to ground
  4. Poor or high-resistance ground connection
  5. Dirty, incorrect or old engine oil affecting the timing system
  6. Failed engine control module (rare)

How to diagnose

  1. Read all codes and freeze frame data, clear the code and see if it returns.
  2. Check oil level and condition, and confirm it meets the manufacturer's spec.
  3. Inspect the Bank 1 solenoid connector and harness for chafing, corrosion, oil and damaged locks.
  4. Measure the solenoid coil resistance with a multimeter and compare it to spec.
  5. Check power and ground at the connector, and test the signal wire for a short to ground.
  6. Command the solenoid with a scan tool and watch for a response.
  7. Test the wiring to the ECM for opens and shorts.
  8. If the circuit is good, check the ECM driver and look for software updates.

Common fixes

  • Replace the exhaust valve control solenoid
  • Repair or replace damaged wiring and connectors
  • Clean and tighten ground connections
  • Change the oil and filter to the specified type
  • Replace or reprogram the ECM (last resort)

Questions and answers

What does P0079 mean?

It means the Bank 1 exhaust valve control solenoid circuit has a low signal. The PCM sees lower voltage than expected, most often due to the solenoid or its wiring.

Can I drive with P0079?

Short, careful trips such as getting to a shop are usually fine. Expect rough running, lost power and higher fuel use, so don't put off the repair.

How do I fix P0079?

Check the oil, the connector and the wiring first, then measure the solenoid resistance. Wiring repair or solenoid replacement fixes most cases.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.