P0079 code definition
Exhaust Valve Control Solenoid Circuit Low (Bank 1)
What the P0079 code means
P0079 indicates an issue that is found when the Engine Control Module (ECM) tries to control the Bank 1 exhaust valve solenoid and finds the system readings to be out of range. Specifically, this code is found when the ECM detects low system voltage. This code is similar to P0078 and P0080.
What causes the P0079 code?
- Faulty exhaust valve control solenoid, Bank 1
- Open or short in wiring harness
- Faulty Engine Control Module
- Poor connection issues or failed connector
What are the symptoms of the P0079 code?
- The ECM sets the Check Engine Light to be illuminated on the dashboard
- The ECM disables variable valve timing (in most cases)
- Vehicle may suffer from poor acceleration
- Poor fuel economy may be noticed.
How does a mechanic diagnose the P0079 code?
Hooks up a scanner to the Data Link Connector (DLC) port to check for all OBD2 codes
Observes the freeze frame data, noting all vehicle conditions such as speed, temperature, coolant temperature, and engine load
Clear the codes and performs a road test to the same conditions noted earlier from the freeze frame data
If the P0079 code returns:
Performs a visual inspection of the exhaust valve control solenoid, Bank 1 harness
Checks all connectors for damage and proper connection
Uses an advanced scan tool to monitor the exhaust valve control solenoid circuit, looking for low system voltage and improper readings
If the control solenoid checks out, then a manufacturer specific test will be performed on the Engine Control Module to test.
Common mistakes when diagnosing the P0079 code
Most common mistakes made when diagnosing P0079 can be avoided by simply following all steps in the proper order and not missing any. The control solenoid must be tested for proper operation before it is replaced to confirm whether it is necessary; replacing the solenoid will only solve the issue if it has failed testing. This code may be only seen intermittently.
How serious is the P0079 code?
The most serious fault associated with this code is usually limited to seeing the Check Engine Light on the dashboard. In addition, the variable valve control system is disabled and goes into failsafe mode, which can cause drivability issues such as poor acceleration and fuel economy. Any fault that causes a failsafe mode should be repaired to allow normal driving and safe operation of the vehicle.
What repairs can fix the P0079 code?
- Replacing the exhaust valve control solenoid
- Repairing or replacing faulty wiring
- Repairing connection issues
- Replacing the ECM
Additional comments for consideration regarding the P0079 code
Bank 1 is typically on the driver's side of the engine. Vehicles with a v configuration such as a V6 or V8 will have a Bank 1 and Bank 2; care should be taken to diagnose the correct side. Bank 1 can be found by finding the number 1 cylinder, typically. The solenoid should be found on the same side as the exhaust manifold.
An advanced level scan tool that is standard issue for professional technicians will be required to diagnose this code, and test the solenoid operation. These professional scan tools can graph data over time and show any changes as the vehicle goes through its operation range. This is required to ensure that the sensor is not replaced without being bad, which would be a waste of valuable time and money.
The exhaust valve control solenoid is part of the variable valve timing system. The variable valve timing is an important part of modern engines. It allows better acceleration and improves fuel economy.
Need help with a P0079 code?
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This article originally appeared on YourMechanic.com as P0079 OBD-II Trouble Code: Exhaust Valve Control Solenoid Circuit Low (Bank 1) and was authored by Spencer Clayton.