The diagnostic trouble code (DTC) P0079 indicates a problem within the exhaust valve control solenoid circuit for Bank 1. This circuit is responsible for controlling the operation of the exhaust valve, often part of a variable valve timing (VVT) or variable valve lift (VVL) system. When the engine control unit (ECU) detects a low voltage signal in this circuit, it triggers the P0079 code, signaling a potential malfunction that requires investigation and repair.
This issue can lead to reduced engine performance, decreased fuel efficiency, and potentially even engine damage if left unaddressed. Prompt diagnosis and repair are crucial to restore optimal engine operation and prevent further complications.
| Topic | Description | Potential Causes |
|---|---|---|
| Definition | Exhaust Valve Control Solenoid Circuit Low (Bank 1) indicates the ECU has detected a lower-than-expected voltage in the control circuit for the exhaust valve solenoid on engine bank 1. | - Short to ground in the exhaust valve control solenoid circuit. - Faulty exhaust valve control solenoid. - Open or high resistance in the exhaust valve control solenoid circuit. - Damaged ECU (rare). |
| Symptoms | Noticeable signs that indicate the presence of the P0079 code. | - Check Engine Light (CEL) illuminated. - Reduced engine power and performance. - Poor fuel economy. - Rough idling. - Engine stalling. - Difficulty starting. |
| Bank 1 Location | Identifies the engine bank where the affected exhaust valve control solenoid is located. | Determined by engine configuration; generally the bank containing cylinder #1. Refer to vehicle-specific repair manual for accurate identification. |
| Exhaust Valve Control Solenoid Function | Explains the purpose and operation of the exhaust valve control solenoid within the VVT/VVL system. | Regulates oil flow to the exhaust valve actuator, which alters the valve timing or lift. This is controlled by the ECU to optimize engine performance and emissions. |
| Common Causes | Lists the most frequent reasons for the P0079 code to be triggered. | - Faulty exhaust valve control solenoid. - Wiring harness or connector damage (corrosion, loose connections, chafing). - Short to ground in the wiring. - Open circuit in the wiring. |
| Diagnostic Steps | Provides a step-by-step approach to diagnosing the P0079 code. | 1. Verify the code with a scan tool. 2. Inspect wiring and connectors to the exhaust valve control solenoid. 3. Test the exhaust valve control solenoid resistance. 4. Check for shorts to ground in the wiring. 5. Check for open circuits in the wiring. 6. Test the ECU output signal to the solenoid. |
| Possible Solutions | Suggests potential repairs and fixes for the P0079 code. | - Replace the faulty exhaust valve control solenoid. - Repair or replace damaged wiring and connectors. - Repair short to ground or open circuit in the wiring. - Replace the ECU (as a last resort, after thorough diagnosis). |
| Tools Required | Lists the necessary tools for diagnosing and repairing the P0079 code. | - OBD-II scan tool. - Multimeter. - Wiring diagram for the specific vehicle. - Basic hand tools (sockets, wrenches, screwdrivers). |
| Related Codes | Lists other DTCs that may appear alongside P0079, indicating a broader system issue. | - P0075, P0076, P0077, P0078 (related to the exhaust valve control solenoid circuit). - P0010, P0011, P0012 (related to the intake valve control solenoid circuit - VVT system issues). |
| VVT/VVL System Overview | Briefly describes the Variable Valve Timing (VVT) and Variable Valve Lift (VVL) systems and their importance in modern engines. | VVT/VVL systems optimize engine performance and efficiency by adjusting the timing or lift of the intake and exhaust valves based on engine speed and load. |
| Importance of Oil Condition | Explains how the condition of the engine oil affects the operation of the exhaust valve control solenoid and the VVT/VVL system. | Dirty or low oil can restrict oil flow to the solenoid and actuator, causing them to malfunction. Regular oil changes are crucial for proper VVT/VVL system operation. |
Detailed Explanations
Definition: The P0079 code, "Exhaust Valve Control Solenoid Circuit Low (Bank 1)," signifies that the vehicle's engine control unit (ECU) has detected a voltage level in the control circuit of the exhaust valve control solenoid on engine bank 1 that is below the expected range. This usually points to a problem within the electrical circuit or the solenoid itself.
Symptoms: The symptoms of a P0079 code can vary, but common indicators include the illumination of the Check Engine Light (CEL), a noticeable reduction in engine power and performance, poor fuel economy, a rough or unstable idle, the possibility of engine stalling, and even difficulty starting the engine. These symptoms arise because the VVT/VVL system isn't functioning correctly due to the solenoid issue.
Bank 1 Location: Bank 1 refers to the side of the engine that contains cylinder number 1. The exact location of Bank 1 depends on the engine configuration (inline, V-shaped, etc.). Consult your vehicle's repair manual for a precise diagram and identification of Bank 1 within your specific engine model.
Exhaust Valve Control Solenoid Function: The exhaust valve control solenoid acts as a regulator, controlling the flow of engine oil to the exhaust valve actuator. This actuator, in turn, alters the timing or lift of the exhaust valve. The ECU precisely commands the solenoid to adjust valve operation, optimizing engine performance, fuel efficiency, and emissions output based on various driving conditions.
Common Causes: The most frequent causes of a P0079 code include a faulty exhaust valve control solenoid, damage to the wiring harness or connectors (such as corrosion, loose connections, or chafing), a short to ground in the wiring, or an open circuit in the wiring. Less commonly, a damaged ECU could be the culprit, but this is typically diagnosed after ruling out other possibilities.
Diagnostic Steps: Diagnosing a P0079 code involves a systematic approach. First, verify the code using an OBD-II scan tool. Next, thoroughly inspect the wiring and connectors leading to the exhaust valve control solenoid for any signs of damage. Then, test the resistance of the solenoid using a multimeter to check for internal faults. Check for shorts to ground in the wiring by testing continuity between the solenoid circuit wiring and the vehicle's chassis. Similarly, check for open circuits in the wiring by testing continuity along the entire circuit. Finally, test the ECU's output signal to the solenoid to ensure the ECU is sending the correct command.
Possible Solutions: Potential solutions for a P0079 code include replacing the faulty exhaust valve control solenoid, repairing or replacing damaged wiring and connectors, repairing any shorts to ground or open circuits in the wiring, and, as a last resort after exhausting all other possibilities, replacing the ECU.
Tools Required: Diagnosing and repairing a P0079 code requires specific tools. An OBD-II scan tool is essential for reading and clearing diagnostic trouble codes. A multimeter is needed for testing voltage, resistance, and continuity. A wiring diagram specific to your vehicle's make and model is crucial for tracing circuits and identifying components. Basic hand tools like sockets, wrenches, and screwdrivers are also necessary for accessing and removing components.
Related Codes: The P0079 code may sometimes appear alongside other DTCs, indicating a broader system issue. Related codes might include P0075, P0076, P0077, and P0078, which are also related to the exhaust valve control solenoid circuit. Additionally, codes like P0010, P0011, and P0012, related to the intake valve control solenoid circuit and general VVT system issues, may also be present.
VVT/VVL System Overview: Variable Valve Timing (VVT) and Variable Valve Lift (VVL) systems are crucial components of modern engines. These systems enhance engine performance and fuel efficiency by dynamically adjusting the timing or lift of the intake and exhaust valves based on engine speed and load. This optimization results in improved power output, reduced emissions, and better fuel economy across a wider range of driving conditions.
Importance of Oil Condition: The condition of the engine oil plays a vital role in the proper functioning of the exhaust valve control solenoid and the entire VVT/VVL system. Dirty or low oil can restrict oil flow to the solenoid and actuator, causing them to malfunction and potentially trigger the P0079 code. Regular oil changes, using the correct type and viscosity of oil as recommended by the vehicle manufacturer, are essential for maintaining optimal VVT/VVL system operation and preventing related issues.
Frequently Asked Questions
What does the P0079 code mean? It indicates a low voltage signal in the exhaust valve control solenoid circuit for bank 1, signaling a potential electrical or solenoid malfunction.
Can I still drive with a P0079 code? While you can drive, it's not recommended. The engine may suffer from reduced performance and fuel economy, and the underlying issue could worsen, leading to further damage.
How do I fix a P0079 code? Diagnosis involves checking wiring, the solenoid, and the ECU. Repair might involve replacing the solenoid, fixing wiring issues, or, rarely, replacing the ECU.
Is the P0079 code serious? Yes, it should be addressed promptly. Ignoring it can lead to further engine damage and increased repair costs.
Can low oil cause a P0079 code? Yes, low or dirty oil can restrict oil flow to the solenoid, causing it to malfunction and trigger the code.
Conclusion
The P0079 code signifies a problem with the exhaust valve control solenoid circuit on Bank 1, which can lead to various engine performance issues. A thorough diagnosis, including checking the solenoid, wiring, and ECU, is crucial for identifying the root cause and implementing the appropriate repair. Addressing this code promptly ensures optimal engine operation and prevents potential long-term damage.