P0079 – Exhaust Valve Control Solenoid Circuit Low Bank 1

P0079 is one of those engine codes that sounds scarier than it usually is, but you still don’t want to ignore it. This code points to a problem with the exhaust valve control solenoid circuit on Bank 1, which affects how your engine breathes and manages emissions. You might notice a rough idle, reduced power, or a check engine light with no obvious drivability issue. In this guide, you’ll learn what P0079 means, common symptoms and causes, how a mechanic diagnoses it, and what it typically costs to repair.

What Does P0079 Mean?

DTC P0079 stands for “Exhaust Valve Control Solenoid Circuit Low (Bank 1).” Your engine uses variable valve timing (VVT) to adjust when the valves open and close. The exhaust valve control solenoid is an electrically controlled valve that directs oil pressure to change exhaust cam timing on Bank 1 (the side of the engine with cylinder #1).

When the engine control unit (ECU) sees a voltage or signal level that’s lower than expected in this solenoid’s control circuit, it sets P0079. This usually indicates an electrical issue such as high resistance, a short to ground, or a failing solenoid coil, rather than a purely mechanical engine problem.

Quick Reference

• Code: P0079
• Meaning: Exhaust valve control solenoid circuit low, Bank 1
• System: Variable valve timing (VVT) / valve control
• Typical causes: Bad solenoid, wiring fault, poor connector, rare ECU fault
• Severity: Moderate – may affect performance and emissions
• Common fix: Repair wiring or replace exhaust VVT solenoid

Real-World Example / Field Notes

In the shop, I see P0079 most often on higher-mileage engines where oil changes were stretched too far. One example: a mid-2000s sedan came in with a check engine light and slightly rough idle, but the owner said it “still runs fine.” Scan tool showed P0079 only. The exhaust VVT solenoid connector was full of old, baked-on oil and dirt, and the harness insulation was cracked. Cleaning the connector, repairing a chafed wire, and replacing the solenoid fixed the issue. After a few drive cycles, the code didn’t return and the idle smoothed out.

Symptoms of P0079

• Check engine light (MIL) – Often the only obvious sign, especially early on.
• Rough idle – Engine may feel shaky or uneven at stoplights.
• Reduced power – Noticeable lack of acceleration, especially at low to mid RPM.
• Poor fuel economy – You may see a drop in MPG due to incorrect valve timing.
• Hesitation or flat spots – Engine may stumble when you first press the throttle.
• Hard starting – In some cases, extended cranking or slow start when warm.
• Failed emissions test – Increased emissions or readiness monitors not completing.

Common Causes of P0079

Most Common Causes

• Faulty exhaust valve control solenoid (Bank 1) – Internal coil failure or sticking solenoid is the top cause. The ECU sees low circuit voltage or current out of range.
• Damaged wiring to the solenoid – Chafed, broken, or corroded wires between the solenoid and ECU can cause a low signal condition.
• Poor electrical connector contact – Loose pins, corrosion, or oil intrusion at the solenoid connector or intermediate harness plugs.
• Low or dirty engine oil – While P0079 is primarily an electrical code, heavily sludged oil can overheat or damage the solenoid and aggravate circuit issues.

Less Common Causes

• ECU (PCM) internal fault – Rare, but a failed driver circuit inside the ECU can cause low voltage to the solenoid.
• Aftermarket remote start or alarm wiring – Poorly installed accessories sometimes tap into engine harness wiring and create resistance or shorts.
• Previous engine work – Incorrectly routed or pinched harness after timing belt, head gasket, or camshaft work.
• Water intrusion – Moisture entering connectors or harness junctions, especially in vehicles driven through deep water or with missing splash shields.

Diagnosis: Step-by-Step Guide

To diagnose P0079 correctly, you’ll want a basic scan tool, a digital multimeter (DMM), and ideally a wiring diagram for your specific vehicle. A capable scan tool that can read live data and Mode $06 information is helpful but not mandatory for a DIYer. Always start with basic visual checks before diving into deeper electrical testing.

1. Confirm the code and check for others
   Plug in a scan tool and confirm P0079 is present. Look for related VVT or camshaft codes (like P0010–P0029). If multiple VVT codes are stored, you may have a shared power or ground problem.
2. Check freeze frame and operating conditions
   Review freeze frame data to see when the code set (RPM, engine temp, load). This can indicate if the fault occurs only when hot or at certain RPM ranges.
3. Visual inspection of solenoid and wiring
   Locate the Bank 1 exhaust valve control solenoid, usually near the exhaust cam or timing cover. Inspect the connector for oil, corrosion, broken locks, or loose pins. Follow the harness for any rubbing, melting, or previous repair splices.
4. Check engine oil level and condition
   Verify the oil is at the correct level and not thick, sludged, or burnt. While this won’t directly cause a low circuit voltage, poor oil can contribute to solenoid overheating or sticking.
5. Electrical connector and pin fit test
   With the key off, unplug the solenoid and inspect the terminals. Lightly tug each wire to ensure it’s secure. If pins are green, white, or oily, clean them with electrical contact cleaner and let them dry completely.
6. Measure solenoid coil resistance
   Using a multimeter, check resistance across the solenoid terminals. Compare the reading to the service manual spec or to the Bank 2 solenoid if your engine has one. A reading that’s open (infinite) or far outside normal range indicates a bad solenoid.
7. Check for power and ground at the connector
   With key on (engine off), back-probe the connector to confirm proper voltage supply and ground. One wire is typically battery or reference voltage, the other is ECU-controlled. If power is missing, trace back to fuses, relays, or shared power feeds.
8. Wiggle test the harness
   While monitoring live data or the solenoid circuit with your meter, gently move the harness in different spots. If the reading drops out or changes when you move it, you’ve likely found a broken or intermittent wire.
9. Check Mode $06 or actuator test (if available)
   On some scan tools, you can command the exhaust VVT solenoid on and off or review Mode $06 data to see if the ECU is detecting borderline performance. This helps confirm if the ECU is sending a signal but the solenoid or wiring isn’t responding correctly.
10. Evaluate ECU only after all else checks out
    If the solenoid, wiring, power, and ground all test good, and the problem persists, an ECU driver fault becomes more likely. At this point, professional diagnosis or ECU testing is recommended before replacement.

Pro tip: If your engine has both Bank 1 and Bank 2 exhaust solenoids and they’re easy to access, swap them side to side. If the code changes to the other bank (for example, becomes P0080), you’ve confirmed the solenoid itself is the problem.

Possible Fixes & Repair Costs

Most P0079 repairs involve addressing the exhaust valve control solenoid or its wiring. In many cases, replacing the solenoid and cleaning the connector solves the issue. If wiring is damaged, you may need to repair or replace sections of the harness, which can be more labor-intensive. ECU replacement is rare but possible on some models.

Typical repair costs vary depending on vehicle make, engine layout, and labor rates:

• Exhaust valve control solenoid replacement: $120–$350 parts and labor.
• Wiring/connector repair: $80–$250, depending on accessibility and extent of damage.
• ECU diagnosis and replacement (if needed): $500–$1,200+, including programming.

Costs are affected by how buried the solenoid is, whether intake or covers must be removed, local labor rates, and whether you use OEM or aftermarket parts.

Can I Still Drive With P0079?

In most cases, you can still drive with P0079 for a short period, especially if the only symptom is a check engine light and mild performance change. However, the engine may not adjust exhaust valve timing correctly, which can lead to reduced power, higher fuel consumption, and increased emissions. If you notice severe rough running, stalling, or poor acceleration, you should avoid driving and have the vehicle inspected as soon as possible. Treat P0079 as a “fix soon” code, not an emergency, but don’t ignore it for months.

What Happens If You Ignore P0079?

Ignoring P0079 long term can cause increased carbon buildup, poor fuel economy, and stress on the catalytic converter due to incorrect exhaust valve timing and mixture control. Over time, this can turn a relatively simple solenoid or wiring repair into more expensive issues, including failed emissions tests and potential damage to other engine components.

Last updated: February 13, 2026

Vehicles Commonly Affected by P0079

P0079 is most common on vehicles with advanced variable valve timing systems. You’ll often see it on:

• Hyundai and Kia 4-cylinder and V6 engines with CVVT systems.
• Volkswagen and Audi engines using electronically controlled cam phasing.
• GM (Chevrolet, GMC, Buick) models with VVT-equipped Ecotec and V6 engines.
• Toyota and Lexus engines with VVT-i, especially higher-mileage vehicles with poor oil change history.
• Subaru models using AVCS (Active Valve Control System) on the exhaust cams.

The code can appear on many other makes as well, but it’s especially frequent on engines where the exhaust VVT solenoids are mounted externally and exposed to heat, oil leaks, and road debris.