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P0078 Code Explained: Exhaust Valve Control Solenoid Circuit High Bank 1 Causes, Symptoms & Fixes

P0078 code shown on an OBD-II scanner beside the Bank 1 exhaust valve control solenoid with highlighted VVT wiring and camshaft actuator.

If your OBD-II scanner displays P0078, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected a higher-than-expected electrical signal in the Bank 1 exhaust valve control solenoid circuit.

The generic OBD-II definition for P0078 is:

Exhaust Valve Control Solenoid Circuit High Bank 1

Depending on the manufacturer, this code may also appear as:

The exhaust valve control solenoid is responsible for controlling oil flow to the Bank 1 exhaust camshaft actuator (cam phaser). By adjusting exhaust valve timing, the ECM can improve engine performance, fuel economy, idle quality, emissions, and turbocharger efficiency.

Unlike timing-performance codes, P0078 is an electrical fault code. It indicates the ECM sees a circuit voltage or feedback signal that remains higher than expected, often because of an open circuit, disconnected solenoid, broken wiring, or a short to battery voltage.

Common causes include:

Typical symptoms include:

For additional diagnostic guides, see:

P0078 Quick Facts

ItemInformation
OBD-II CodeP0078
DescriptionExhaust Valve Control Solenoid Circuit High Bank 1
CategoryPowertrain
SystemVariable Valve Timing (VVT)
SeverityModerate
Safe to Drive?Usually for short distances
Typical Repair Cost$100–$900

What Does P0078 Mean?

P0078 means the ECM detects the Bank 1 exhaust valve control solenoid circuit remains at a voltage higher than its expected operating range.

This commonly happens because:

Unlike P0079 (performance/intermittent faults), P0078 specifically indicates an electrical high-voltage condition.

What Is the Exhaust Valve Control Solenoid?

The exhaust valve control solenoid is an electronically controlled oil valve that regulates oil pressure to the exhaust camshaft actuator.

Manufacturers may call it:

The ECM constantly adjusts exhaust valve timing based on:

This improves:

How the Circuit Works

Most exhaust VVT solenoids use:

The PCM rapidly switches the ground circuit using pulse-width modulation (PWM).

The ECM monitors:

If the ECM commands the circuit low but continues seeing battery voltage, it stores P0078.

What Does “Circuit High” Mean?

“Circuit High” refers to the electrical signal, not engine oil pressure.

It typically means:

It does NOT mean:

Symptoms of P0078

Drivers may notice:

Many vehicles simply disable variable valve timing until repairs are completed.

Common Causes of P0078

1. Failed Exhaust VVT Solenoid

The internal winding can fail, producing:

2. Open Solenoid Coil

An open coil prevents current flow entirely.

The ECM sees battery voltage remaining on the circuit.

3. Disconnected Connector

One of the most common causes after engine work.

Always verify the connector is fully locked.

4. Broken Wiring

Damaged wiring near the cylinder head commonly causes:

Inspect for:

5. Short to Battery Voltage

The control wire may contact:

This prevents the PCM from properly controlling the solenoid.

6. Corroded Connector

Corrosion increases resistance and interrupts normal current flow.

Inspect for:

7. Failed Fuse or Relay

If the power supply is abnormal, the ECM may detect incorrect voltage behavior.

Inspect shared VVT fuses and relays.

8. Incorrect Replacement Solenoid

Wrong aftermarket parts sometimes have:

Always verify OEM specifications.

9. PCM Driver Failure

Rare, but possible after:

Always eliminate external wiring faults first.

Is P0078 Serious?

P0078 is considered moderately serious.

The vehicle usually remains drivable, but:

Driving should be avoided if:

Can You Drive With P0078?

Usually yes—for a short distance.

Do not continue driving if:

How to Diagnose P0078

Step 1

Scan all stored codes.

Look for related codes including:

Step 2

Verify oil level and oil condition.

Dirty oil won’t usually create P0078 directly, but it can contribute to VVT problems.

Step 3

Locate the Bank 1 exhaust VVT solenoid.

Inspect:

Step 4

Measure coil resistance.

Compare with factory specifications.

Infinite resistance usually indicates an open coil.

Step 5

Verify power supply.

Confirm:

Step 6

Check the control wire.

Inspect for:

Step 7

Command the solenoid using a bidirectional scan tool.

Watch:

Step 8

Repair the fault.

Clear codes.

Complete a drive cycle.

Verify P0078 does not return.

Common Repairs

RepairTypical Cost
Reconnect connector$0–50
Repair wiring$150–600
Replace VVT solenoid$150–500
Replace connector$100–250
Oil service$60–180
Replace PCM$1,000–2,500

Common Diagnostic Mistakes

Avoid these errors:

Sometimes the “major engine problem” turns out to be a connector that was left unplugged during yesterday’s valve cover gasket replacement. Humbling? Yes. Expensive? Only if you skip the basics.

Frequently Asked Questions

What does P0078 mean?

The ECM detects a high electrical signal in the Bank 1 exhaust valve control solenoid circuit.

Can a bad VVT solenoid cause P0078?

Yes.

An open internal coil is one of the most common causes.

Can dirty oil cause P0078?

Not directly.

Dirty oil causes hydraulic VVT problems, while P0078 is primarily an electrical circuit fault.

Can I drive with P0078?

Usually for a short distance, provided there are no oil pressure warnings or severe drivability issues.

Is P0078 expensive to fix?

Most repairs range from $150–500.

Major wiring repairs or PCM replacement increase costs significantly.

Final Thoughts

P0078 indicates that the Bank 1 exhaust valve control solenoid circuit remains electrically high, preventing the ECM from properly controlling exhaust camshaft timing.

The most common repairs involve:

Begin with the simple checks first. Variable valve timing may sound like advanced engineering—and it is—but more than a few P0078 repairs have ended with the timeless automotive diagnosis of, “Yep… that connector was never plugged back in.”

Related Articles

Continue your diagnosis with these Pro Street guides:

You can also browse the complete OBD-II Diagnostic Code Library, plus the B-Code and C-Code libraries on Pro Street Online.

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