P0079 — Exhaust Valve Control Solenoid

The diagnostic trouble code P0079 generally indicates an issue related to the exhaust valve control solenoid. This component is part of the vehicle’s variable valve timing (VVT) system, which optimizes engine performance, fuel efficiency, and emissions by controlling the exhaust valve timing. When this code appears, it suggests that the vehicle’s engine management system has detected a fault affecting the operation of this solenoid. Please note that labels for this code may vary slightly depending on the OEM (Original Equipment Manufacturer).

Manufacturer variations for trouble code P0079

Depending on the manufacturer, the P0079 code may be stored under different labels or with different code formats. These variations are standard practice as each OEM may assign specific codes to particular engine or system issues. Common label variations include:

• Ford: P0079
• Honda: P0079
• Mercedes-Benz: 0079
• BMW: P0079
• Hyundai/Kia: P0079
• Other brands: Similar codes with slight variations, but P0079 remains most common

What does trouble code P0079 mean?

In simple terms, P0079 indicates that the vehicle’s engine control module (ECU) has detected a problem with the exhaust valve control solenoid. This component is responsible for adjusting the timing of the exhaust valves in some engines—particularly those equipped with variable valve timing systems. The ECU monitors signals from sensors and compares them to expected parameters. When the solenoid’s operation deviates from the norm—due to electrical or mechanical issues—the code P0079 is triggered.

This code typically appears in contexts where there is a malfunction in the VVT system, which can affect engine efficiency, emissions, and performance. It may occur gradually as components wear, or suddenly if an electrical fault occurs. Recognising the circumstances of its appearance helps target the root cause during diagnosis.

Severity and risks of trouble code P0079

The severity of P0079 involves the potential impact on engine performance and emissions. If left unaddressed, it can lead to decreased fuel economy, increased emissions, rough idling, or even engine damage in severe cases. While sometimes the vehicle can continue to operate, ongoing issues may cause further damage or reduce drivability.

In most situations, driving with this code is limited. It’s advisable not to ignore it for long—especially if accompanied by noticeable symptoms—because continuing to drive could stress other engine components or lead to more costly repairs.

Symptoms of trouble code P0079

The presence of P0079 can manifest through various engine symptoms. Although not always all symptoms present, common signs include:

• Reduced engine performance or power loss, especially during acceleration
• Rough idling or stalling
• Decreased fuel efficiency
• Illuminated check engine light
• Erratic engine behaviour or hesitation during throttle changes
• In some vehicles, exhaust noise or abnormal engine sounds

Most likely causes of trouble code P0079

The causes of P0079 revolve around electrical, mechanical, or sensor-related issues affecting the exhaust valve control solenoid. Here are the most common causes, ordered from most to least typical:

1. Electrical Faults: Damaged wiring, poor connections, or blown fuses affecting the solenoid’s circuit
2. Faulty Exhaust Valve Control Solenoid: The solenoid itself may be defective or worn out, preventing proper operation

3. Engine Oil Issues: Low or dirty oil can interfere with solenoid activation, especially if the system relies on oil pressure or quality for operation

4. Hydraulic or Mechanical Blockages: Build-up or blockage within the VVT system that impairs the movement or response of the exhaust valve mechanism

5. ECU Software or Sensor Malfunction: Less common, but possible, where a software fault or malfunctioning sensor gives incorrect signals to the ECU

How to diagnose trouble code P0079

Diagnosing P0079 involves a systematic approach to identify electrical, mechanical, or sensor failures. Here are general steps to follow:

1. Visual Inspection: Check wiring harnesses, connectors, and fuses related to the VVT system for signs of damage or corrosion.
2. Scan Live Data: Use an OBD-II scanner capable of reading live sensor parameters. Confirm the status of the exhaust valve control solenoid and related sensors.
3. Inspect the Solenoid and Circuit: Test the solenoid’s electrical resistance and verify circuit continuity with a multimeter.
4. Check Oil Condition and Level: Ensure that engine oil is at proper level and free of contaminants, as oil quality can influence the system.
5. Perform Functional Tests: Command the solenoid on and off via the scanner, observing if it responds correctly or if there are anomalies.
6. Evaluate Sensors: Confirm the proper functioning of related sensors, such as the camshaft position sensor, which may influence the VVT system’s operation.

Possible repairs for trouble code P0079

Addressing P0079 involves repairs targeting electrical, mechanical, or software issues identified during diagnosis. The following actions are common:

• Replace or Repair Wiring and Connectors: Professional repair or replacement of damaged wiring harnesses, ensuring proper connections and insulation.
• Replace the Exhaust Valve Control Solenoid: If the solenoid is defective, replacing it with OEM or equivalent quality parts is essential. This is usually a professional repair.
• Change Engine Oil: If oil quality or level is the issue, perform an oil change with recommended specifications to restore proper lubrication and system operation.
• Clean or Unblock the VVT System: Mechanical cleaning or removal of obstructions within the system may be necessary, often performed by a qualified technician.
• Update ECU Software: In some cases, a software update may resolve operational discrepancies, but this requires dealer or expert intervention.

Vehicles commonly associated with trouble code P0079 in Europe

Although the specific prevalence varies, P0079 is frequently found in certain vehicle brands and engine families recognized for their VVT systems. Typically associated models include:

Ford: Focus, Fiesta, Mondeo (with Ecoboost engines)

Honda: Civic, Accord (certain models with variable valve timing)

Mercedes-Benz: E-Class, C-Class (with VVT engines)

BMW: 3 Series, 5 Series (with VALVETRONIC engines)

Hyundai/Kia: Elantra, Kia Sorento (vehicles with Gamma or Nu engines)

Frequent mistakes with trouble code P0079

When diagnosing or repairing P0079, some common pitfalls can lead to unnecessary costs or missed faults. Preventing these mistakes ensures more accurate diagnosis and effective repairs:

• Assuming the problem is solely electrical without visual inspection: Electrical issues may originate from mechanical failures or vice versa.
• Ignoring related sensors or system components: Focusing only on the solenoid without checking the camshaft or crankshaft sensors can overlook root causes.
• Replacing parts without proper testing: Swapping components like the solenoid or wiring without proper diagnostics may lead to unnecessary expenses.
• Overlooking engine oil condition: Poor oil quality can mimic electrical failures, yet is often overlooked.

FAQ — trouble code P0079

Can this code disappear on its own? In some cases, temporary issues like electrical glitches or sensor anomalies can clear themselves, especially after a restart, but persistent P0079 indicates an underlying fault that needs rectification.

Can I keep driving? It depends on your symptoms. Mild symptoms or a stored, inactive code may allow safe driving temporarily, but prolonged driving with this code can risk further damage or emission non-compliance. It’s best to diagnose and repair promptly.

Why does the code return after clearing? If the root cause—be it wiring, the solenoid, or mechanical blockage—is not addressed, the fault will likely recur as soon as the ECU performs its self-test and detects the problem again.