P0078

Universal

Exhaust Valve Control Circuit (Bank 2)

Definition source: General OBD-II reference catalog

Definition verification: Not independently verified for display.

Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium

Medium Severity

The engine computer has detected an electrical fault in the circuit controlling exhaust-valve operation on Bank 2. This circuit may operate a valve-timing control component, depending on the vehicle. The code does not by itself prove that a particular part has failed, and the engine may still run normally.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the engine runs very roughly, loses significant power, stalls, or the check-engine light flashes, stop driving when it is safe and arrange an inspection. Otherwise, drive cautiously and have the fault diagnosed soon. Follow the vehicle manual if an oil-pressure warning appears.

Common Symptoms

The check-engine light may be on, while the vehicle shows no noticeable change.
Reduced power or sluggish acceleration may occur if exhaust-valve control is limited.
Rough idle or uneven running may occur if valve operation is affected.
Fuel economy or emissions may worsen if exhaust-valve timing is not controlled as intended.

Common Causes

Damaged, loose, or corroded wiring or connectors in the Bank 2 control circuit.
An electrical fault in the exhaust-valve control solenoid or actuator.
A problem with circuit power, ground, or a related fuse, where applicable.
A fault in the engine computer's circuit driver, considered only after the wiring and controlled component are checked.
A mechanical or oil-related issue may affect valve-control operation, but does not by itself establish the cause of this circuit code.

Diagnostic Steps

Check whether the engine runs abnormally and note any other warning lights or symptoms; stop driving if it stalls, runs severely rough, or loses substantial power.
Use the owner’s manual to identify the correct engine oil specification, then check the oil level and condition as directed. This is a general valve-control check, not proof of the electrical fault’s cause.
With the engine off and cool, visually inspect accessible Bank 2 wiring and connectors for looseness, corrosion, damaged insulation, or contact with hot or moving parts. Avoid pulling on wires.
If you have a suitable scan tool, record the codes and available related data before clearing anything. A basic code reader cannot confirm which part has failed.
If the code returns or symptoms are present, ask a qualified technician to test the circuit and control component using vehicle-specific service information.

When to Call a Professional

Confirm the code and check for related codes, then inspect Bank 2 wiring and connectors. A technician can use scan data and supported actuator tests, and test the circuit and control component against vehicle-specific service information. Verify wiring and power or ground faults before considering a control-module fault or replacing parts.

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Commonly Asked Questions

Does P0078 prove the Bank 2 exhaust valve control solenoid is bad?

No. The code points to a fault detected in the control circuit. Wiring, connectors, power or ground, the controlled component, and in less common cases the engine computer need to be checked before choosing a repair.

What does Bank 2 mean?

On an engine with two banks of cylinders, Bank 2 is the bank that does not contain cylinder 1. Its exact location depends on the engine layout.

Can the vehicle have P0078 with no symptoms?

Yes. The check-engine light may be the only noticeable sign. A lack of symptoms does not identify the cause or confirm that the fault has gone away.

Is this code about actual valve timing or an electrical circuit?

The definition identifies the exhaust valve control circuit. A circuit fault can interfere with valve control, but the code alone does not establish whether the underlying issue is electrical, mechanical, or related to another system condition.

Can I keep driving with P0078?

If the vehicle runs normally, cautious short-term driving may be possible, but arrange diagnosis soon. Stop when safe if it stalls, runs severely rough, loses significant power, or displays an oil-pressure warning.

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