P0079 Exhaust Valve Control Solenoid Circuit Low (Bank 1)

A P0079 trouble code can look straightforward because it specifically points toward the exhaust valve control solenoid circuit. However, the word “Low” is important here. It does not necessarily mean that the engine has low oil pressure, low camshaft position, or that the exhaust valve itself is stuck.

The code means the engine control module (ECM/PCM) has detected an electrical condition in the Bank 1 exhaust valve control solenoid circuit that is lower than the expected value.

That distinction matters because replacing the solenoid immediately may not solve the problem. A damaged wire, poor connector, short to ground, or a problem with the control circuit can produce exactly the same code.

What Is the Exhaust Valve Control Solenoid?

Modern engines often use variable valve timing (VVT) to change when the exhaust valves open and close.

The camshaft does not always need to operate with one fixed timing position. Depending on engine speed, load, temperature, and other operating conditions, the ECM may command the exhaust camshaft to advance or retard.

The exhaust valve control solenoid, often called a VVT solenoid, controls engine oil flow to the camshaft timing actuator.

A simplified sequence is:

ECM command → VVT solenoid → oil flow → camshaft actuator → exhaust camshaft position

The solenoid itself is electrically controlled, but its job ultimately affects a hydraulic and mechanical system.

This is why P0079 can involve more than just an electrical component.

What Does “Bank 1” Mean?

Bank 1 identifies the cylinder bank that contains cylinder number 1.

On an inline four-cylinder or inline six-cylinder engine, there is normally only one cylinder bank, so Bank 1 is the only bank.

On V6, V8 and other engines with two cylinder banks, Bank 1 is one side and Bank 2 is the opposite side.

The exact location of the exhaust valve control solenoid depends on the engine design. It may be mounted directly on the cylinder head or near the camshaft timing mechanism.

The Important Part of P0079: What Does “Low” Mean?

This is where P0079 is frequently misunderstood.

“Low” primarily describes the electrical condition of the control circuit.

It does not automatically mean:

• low engine oil pressure

• low VVT pressure

• low exhaust pressure

• low engine power

• low camshaft position

• insufficient exhaust flow

The ECM monitors the electrical circuit controlling the exhaust valve control solenoid. If the circuit voltage or current behavior is outside the expected range in the low direction, it can set P0079.

Depending on the vehicle's circuit design, a low condition can be caused by a short to ground, an internally faulty solenoid, wiring damage, or a control-side problem.

How the Fault Can Actually Develop

Consider two engines that both display P0079.

In the first engine, the VVT solenoid has developed an internal electrical fault. The solenoid's internal resistance is no longer within the expected range, causing the control circuit to behave incorrectly.

In the second engine, the solenoid itself is perfectly functional, but part of the wiring harness has rubbed against the engine and shorted toward ground.

Both vehicles can produce P0079.

This is why the diagnostic process should not begin with “replace the solenoid.”

The correct question is:

Why is the Bank 1 exhaust valve control solenoid circuit being pulled lower than the ECM expects?

Common Causes of P0079

Several faults can create this condition.

Short to ground

A damaged wire touching the engine, cylinder head, or another grounded component can pull the control circuit low.

Faulty exhaust VVT solenoid

The solenoid may have an internal electrical problem. A shorted winding or another internal failure can alter the current flowing through the circuit.

Damaged wiring

Heat, oil contamination, vibration and contact with moving engine components can damage the wiring insulation.

Corroded or loose connector

A connector may appear connected while its terminals are corroded, spread, contaminated with oil or unable to maintain proper contact.

Incorrect previous repair

After engine or cylinder-head work, wiring can sometimes be routed incorrectly, trapped under a component or connected to the wrong location.

ECM/PCM control problem

The engine computer controls the solenoid circuit. Although less common than wiring or solenoid problems, an internal driver fault is possible.

Oil-related VVT problems

Dirty oil, incorrect oil viscosity, sludge or restricted oil passages can prevent the VVT system from operating correctly. However, an oil problem by itself does not automatically explain an electrical “Circuit Low” code.

What Symptoms Can P0079 Cause?

The symptoms depend heavily on the engine and how much the exhaust camshaft timing is affected.

Some vehicles may continue to drive almost normally apart from the check engine light.

Others can experience:

• Check Engine Light

• rough or unstable idle

• hesitation during acceleration

• reduced engine performance

• poor throttle response

• reduced fuel economy

• difficult starting

• engine stalling

• lack of low-speed torque

• weak acceleration at certain RPM ranges

• increased emissions

• limp-home or reduced-power operation

In some engines, the symptoms are particularly noticeable when accelerating from low RPM because the engine relies heavily on variable valve timing to produce torque.

Why a VVT Electrical Problem Can Affect Engine Performance

The ECM constantly changes valve timing according to operating conditions.

At one engine speed, a particular camshaft position may improve torque. At another speed, a different position may improve airflow and efficiency.

If the exhaust camshaft cannot move to the commanded position, the engine may continue operating with an unsuitable valve timing position.

This can affect the relationship between:

• intake airflow

• exhaust gas flow

• combustion timing

• engine speed

• load

• torque production

As a result, a relatively small electrical problem in the solenoid circuit can eventually create noticeable engine performance symptoms.

Start Diagnosis With the Wiring, Not the Parts Catalog

A good diagnosis of P0079 should begin with the complete fault-code picture.

If the vehicle has additional codes relating to camshaft position, VVT performance, low oil pressure, or other electrical circuits, they can provide important clues.

Freeze-frame data can also help show what the engine was doing when the code appeared.

Then inspect the Bank 1 exhaust valve control solenoid and its wiring.

Look carefully for:

• melted insulation

• wires touching hot exhaust components

• oil inside the connector

• broken connector locks

• corrosion

• loose terminals

• stretched wiring

• previous splices

• harness damage near the cylinder head

The connector should not be considered good simply because it looks connected.

Testing the Solenoid

The exhaust valve control solenoid can be electrically tested according to the manufacturer's procedure.

Its resistance can be measured, but there is no universal resistance value that applies to every engine.

The correct specification depends on the vehicle and solenoid design.

A resistance measurement that is normal on one engine may be completely wrong on another.

More importantly, resistance alone does not prove that a VVT solenoid works correctly under operating conditions.

A proper diagnostic procedure may also involve checking:

• supply voltage

• control-side operation

• current draw

• electrical continuity

• short-to-ground condition

• short-to-power condition

• ECM command

• solenoid response

• camshaft commanded position

• camshaft actual position

Check the Engine Oil Too

Because the solenoid operates the VVT system through engine oil, oil condition should not be ignored.

Check:

• oil level

• oil specification

• oil viscosity

• oil condition

• signs of sludge

• oil-change history

• contamination

If the engine has severe sludge, the VVT oil passages can become restricted.

The solenoid may receive the correct electrical command but still fail to move the camshaft correctly because the hydraulic portion of the system cannot respond.

This creates an important diagnostic distinction:

P0079 points to an electrical circuit condition, but the vehicle may also have a separate mechanical or hydraulic VVT problem.

Check Commanded and Actual Camshaft Position

On vehicles with suitable scan-tool data, this can be one of the most useful tests.

The ECM may command a particular exhaust camshaft position and monitor the actual camshaft position through the camshaft position sensor.

If the command changes but the actual position does not respond, the problem may extend beyond the electrical circuit.

Possible causes can include:

• restricted oil flow

• faulty VVT actuator

• sticking camshaft mechanism

• incorrect engine timing

• camshaft position sensor problems

• mechanical damage

If the solenoid circuit itself is confirmed faulty, however, the electrical problem should be resolved first.

Could Low Engine Oil Cause P0079?

It can contribute to VVT problems, but the answer needs some qualification.

Low or poor-quality engine oil can interfere with variable valve timing operation because the camshaft actuator depends on oil pressure and flow.

However, P0079 specifically identifies a low electrical condition in the exhaust valve control solenoid circuit.

Therefore, simply adding oil and clearing the code is not a proper diagnosis.

If the oil level is low, correct it. But the solenoid circuit should still be electrically inspected.

P0079 Does Not Automatically Mean the Solenoid Is Bad

This is probably the most important point when dealing with this code.

A diagnostic trouble code identifies the system and condition the ECM has detected. It does not necessarily identify the failed component.

For P0079, the possible fault path can look like:

ECM → wiring → connector → VVT solenoid → oil control → camshaft actuator → camshaft position feedback

The actual failure could be anywhere relevant to that chain.

Replacing the solenoid without testing the wiring can therefore result in an unnecessary repair.

P0079 vs P0078

These codes are closely related.

P0078 – Exhaust Valve Control Solenoid Circuit (Bank 1)

This is a broader circuit malfunction code.

P0079 – Exhaust Valve Control Solenoid Circuit Low (Bank 1)

This specifies that the electrical circuit has been detected in a low condition.

So P0079 provides more information about the nature of the electrical fault than P0078.

P0079 vs P0080

P0080 is generally associated with:

Exhaust Valve Control Solenoid Circuit High (Bank 1)

The distinction is important.

P0079 indicates a low circuit condition, while P0080 indicates a high circuit condition.

The physical causes can overlap, but the electrical behavior detected by the ECM is different.

A technician should therefore diagnose the circuit according to the manufacturer's wiring diagram rather than assuming every VVT code requires the same repair.

Can You Drive With P0079?

Sometimes the vehicle can still be driven, especially if the only symptom is the Check Engine Light and the engine is running normally.

But continued driving is not ideal.

A VVT problem can affect fuel economy, emissions and engine performance. If the camshaft timing becomes significantly incorrect, the vehicle may develop rough running, stalling or reduced power.

Driving should be avoided or minimized if you experience:

• severe engine shaking

• major power loss

• repeated stalling

• abnormal engine noise

• low oil-pressure warning

• severe misfire

• flashing Check Engine Light

In particular, an oil-pressure warning should never be treated as simply another VVT fault.

The Correct Repair Depends on What the Test Finds

If testing confirms an internally shorted exhaust VVT solenoid, replacing the solenoid may solve the problem.

If the wiring is shorted to ground, the wiring must be repaired correctly.

If the connector terminals are damaged, the connector or terminals may need repair.

If the electrical circuit is functioning correctly but the camshaft does not respond, attention should move toward the hydraulic and mechanical VVT system.

And if the circuit and mechanical system are both confirmed good, the ECM control side may need further investigation.

This is why P0079 should be approached as a diagnostic path, rather than a parts-replacement instruction.

Final Takeaway

P0079 means the engine control module has detected a low electrical condition in the Bank 1 exhaust valve control solenoid circuit.

The exhaust VVT solenoid is responsible for controlling oil flow to the mechanism that changes exhaust camshaft timing. When its electrical control circuit develops a problem, the engine may lose the ability to adjust valve timing as commanded.

The most common areas to investigate are the solenoid, wiring, connector and circuit control, followed by the oil supply and mechanical VVT system when the electrical side checks out.

The key is not to interpret “Low” as simply “low oil pressure” and not to assume that the solenoid itself is automatically defective. A proper diagnosis follows the circuit from the ECM to the solenoid and then verifies whether the camshaft timing system responds as commanded.