OBDII Error Code P0079: Exhaust Valve Control Solenoid Circuit Low (Bank 1)

As a content creator for autelfrance.com and an expert in auto repair, this article will provide a comprehensive guide on the OBDII error code P0079, specifically focusing on the keyword “Eobd/obdii Error P0079”. This guide aims to be more informative and SEO-optimized for an English-speaking audience than the original article.

Understanding the P0079 Code

The error code P0079 indicates a problem within the exhaust valve control solenoid circuit low for Bank 1 of your engine. This diagnostic trouble code (DTC) signals that the Engine Control Module (ECM) has detected an abnormally low voltage in the control circuit for the exhaust valve solenoid on engine bank 1. This malfunction can impact your vehicle’s engine performance and fuel efficiency.

Vehicles Commonly Affected by Code P0079:

While P0079 is a generic OBDII code, it is frequently observed in vehicles from various manufacturers, including:

Audi: A4, A5, Q5
BMW: 1 Series, 3 Series, X5
Mercedes-Benz: C-Class, E-Class, GLC
Volkswagen: Golf, Passat, Tiguan
Volvo: S60, XC60, XC90
Ford: Escape, Focus, Fusion
Chevrolet: Cruze, Equinox, Malibu
Toyota: Camry, Corolla, RAV4
Honda: Accord, Civic, CR-V
Nissan: Altima, Rogue, Sentra

Decoding the P0079 OBDII Error

To properly understand the P0079 code, it’s crucial to break down the components involved. The Engine Control Module (ECM) is the central computer of your vehicle, responsible for monitoring and regulating numerous engine functions to ensure optimal performance and minimize emissions.

In this context, the ECM is attempting to control the exhaust valve control solenoid for Bank 1. The exhaust valve solenoid plays a vital role in the vehicle’s exhaust system. It regulates the flow of exhaust gases by opening and closing the exhaust valve at precise moments, contributing to efficient engine operation.

When the ECM registers a “circuit low” condition for the P0079 code, it signifies that the voltage in the control circuit of the Bank 1 exhaust valve solenoid is lower than expected. This low voltage reading points towards a potential issue within the electrical circuit or with the solenoid itself.

It’s worth noting that P0079 is part of a family of codes related to exhaust valve control solenoid issues, including P0078 and P0080. These codes provide mechanics with valuable starting points when diagnosing exhaust system problems.

Potential Causes of the P0079 Error Code

Several factors can trigger the P0079 code. Identifying the root cause is essential for effective repair. Common culprits include:

Faulty Exhaust Valve Control Solenoid (Bank 1): The solenoid itself might be malfunctioning, preventing proper electrical signal or mechanical operation. This is the most direct cause related to the code’s definition.
Wiring Harness Issues: Damage to the wiring harness connecting the exhaust valve control solenoid to the ECM can cause a short circuit, open circuit, or increased resistance, leading to a low voltage reading. This includes frayed wires, corrosion, or breaks in the wiring.
ECM Malfunction: In rarer cases, a defective ECM might be sending incorrect signals or misinterpreting feedback from the solenoid circuit. While less frequent, ECM issues should be considered, especially after ruling out other causes.
Poor Electrical Connections: Loose or corroded connectors in the solenoid circuit can disrupt electrical flow, leading to a “circuit low” condition. This includes connectors at the solenoid, ECM, and along the wiring harness.

Symptoms Associated with OBDII Code P0079

When the P0079 code is present, you may observe several symptoms affecting your vehicle’s performance:

Check Engine Light Illumination: This is the most immediate and common symptom. The ECM activates the Check Engine Light on the dashboard to alert the driver of a detected issue.
Variable Valve Timing (VVT) System Disablement: The ECM may disable the VVT system as a precautionary measure to protect the engine from potential damage. This is because the exhaust valve control is crucial for VVT operation.
Reduced Engine Performance/Poor Acceleration: With the VVT system potentially disabled and exhaust valve control compromised, you might experience sluggish acceleration and a general decrease in engine power.
Decreased Fuel Economy: Engine inefficiency due to improper valve timing and exhaust flow can lead to increased fuel consumption, resulting in noticeable poor fuel economy.

Diagnosing the P0079 Code: A Mechanic’s Approach

A skilled mechanic will follow a systematic approach to diagnose the P0079 code accurately:

Initial OBDII Scan: The mechanic will connect an OBDII scanner to the vehicle’s Data Link Connector (DLC) port. This retrieves all stored DTCs, providing a starting point for diagnosis.
Review Freeze Frame Data: Analyzing freeze frame data is crucial. This data captures vehicle parameters (speed, engine temperature, etc.) at the moment the P0079 code was triggered, helping to understand the conditions under which the fault occurred.
Code Clearing and Test Drive: After noting the freeze frame data, the mechanic will clear the codes and perform a test drive under similar conditions to see if the P0079 code reappears. This verifies if the fault is consistent or intermittent.

If the P0079 code returns, the mechanic will proceed with more in-depth diagnostics:
Visual Inspection: A thorough visual inspection of the Bank 1 exhaust valve control solenoid, wiring harness, and connectors is performed. This aims to identify any obvious damage, such as frayed wires, corrosion, or loose connections.

Alt text: Mechanic performing a visual inspection of engine components, checking for wiring and connector issues related to the exhaust valve control solenoid.
Connector and Wiring Checks: Each connector in the circuit is carefully inspected for damage, corrosion, and proper connection. Wiring is checked for continuity and shorts using a multimeter.

Alt text: Close-up of a mechanic using a multimeter to check the voltage and continuity of an electrical connector in a car engine, during diagnosis of OBDII code P0079.
Advanced Scan Tool Circuit Monitoring: An advanced scan tool is used to monitor the exhaust valve control solenoid circuit in real-time. This allows the mechanic to observe voltage readings and identify any inconsistencies or low voltage conditions.
Exhaust Valve Control Solenoid Testing: If circuit issues are ruled out, the solenoid itself is tested. This may involve checking its resistance and ability to actuate properly using manufacturer-specific procedures or specialized tools.
ECM Testing (Last Resort): If the solenoid tests fail and wiring is confirmed good, ECM malfunction is considered. Manufacturer-specific ECM tests are performed to determine if the ECM is the source of the problem.

Common Diagnostic Mistakes to Avoid with P0079

Accurate diagnosis is key to resolving P0079 effectively. Common mistakes to avoid include:

Premature Solenoid Replacement: Avoid replacing the exhaust valve control solenoid without thorough testing. Wiring issues or ECM problems can also cause P0079, and solenoid replacement alone might not fix the underlying problem. Always test before replacing parts.
Ignoring Intermittent Codes: P0079 can sometimes be intermittent. Don’t dismiss it if it doesn’t reappear immediately. Thorough testing and symptom analysis are crucial even with intermittent faults.

Severity of the P0079 Code

While the P0079 code is not indicative of a catastrophic engine failure, it should not be ignored. The primary concern is the potential disabling of the variable valve timing (VVT) system and the engine entering a fail-safe mode.

In fail-safe mode, engine performance is limited, and fuel economy suffers. While drivable, prolonged operation in this mode is not recommended and can lead to:

Continued Poor Performance: Reduced power and acceleration remain until the issue is resolved.
Worsening Fuel Economy: Increased fuel consumption adds to running costs.
Potential for Further System Damage: While less likely in the short term, neglecting electrical faults can sometimes lead to further component damage over time.

Therefore, addressing the P0079 code promptly is advisable to restore optimal engine performance, fuel efficiency, and prevent potential long-term issues.

Repair Solutions for OBDII Error Code P0079

The necessary repairs for P0079 depend on the underlying cause identified during diagnosis. Common solutions include:

Exhaust Valve Control Solenoid Replacement (Bank 1): If testing confirms a faulty solenoid, replacement with a new, quality solenoid is the primary solution.

Alt text: A brand new exhaust valve control solenoid component, ready for installation in the engine to resolve OBDII code P0079.
Wiring Harness Repair or Replacement: If damaged wiring is found, repair or replacement of the affected section of the wiring harness is necessary. This might involve splicing wires, replacing connectors, or replacing the entire harness section.
Electrical Connection Repair: Cleaning corroded connectors, tightening loose connections, and ensuring proper contact are crucial steps in addressing connection-related issues.
ECM Replacement (Rare): If the ECM is diagnosed as faulty (after ruling out all other possibilities), ECM replacement and reprogramming may be required. This is a less common and more expensive repair.

It is highly recommended to have repairs performed by a qualified mechanic to ensure proper diagnosis and correct repair procedures are followed.

Estimated Cost for P0079 Diagnosis and Repair

The cost to diagnose and repair the P0079 error code can vary based on several factors:

Vehicle Make, Model, and Year: Parts and labor costs can differ between vehicle manufacturers and models.
Complexity of the Fault: Whether it’s a simple solenoid replacement or a more complex wiring issue impacts labor time.
Labor Rates: Workshop labor rates vary by location and shop type.

Typically, the diagnostic process begins with an OBDII scan. Many workshops offer a basic scan for a fee.

For a comprehensive diagnostic service, which is recommended for P0079, costs can start from around $60 – $150 USD. This includes a thorough diagnosis to pinpoint the root cause, not just reading the code.

Repair costs will depend on the necessary parts and labor. A solenoid replacement might range from $150 to $400 USD or more, including parts and labor. Wiring repairs can vary, while ECM replacement is significantly more expensive.

It’s always advisable to get a quote from a reputable repair shop for your specific vehicle and the diagnosed fault. Choosing a workshop that offers a comprehensive diagnostic approach ensures accurate problem identification and the most effective repair, saving time and money in the long run.