P0078 Code: Meaning, Symptoms, Causes & Fix

Overview

P0078 is triggered when monitoring logic identifies an issue with Exhaust Valve Control Circuit (Bank 2) affecting powertrain controls.

Symptoms

check engine light
rough operation in certain conditions
reduced performance

Common causes

Disconnected or loose connector affecting exhaust valve control circuit (bank 2)
Broken terminal inside harness
Connector pin damage/corrosion or harness stress near related components

How to diagnose P0078

Confirm P0078 and capture freeze-frame data with a professional scan tool.
Inspect wiring, connectors, and grounds related to exhaust valve control circuit (bank 2) for obvious defects.
Use a continuity test from module pin to component to identify opens/high resistance.
Check for related DTCs to identify the root-cause chain before replacing parts.
After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code P0078

Moderate: This code is moderate severity: the vehicle may still operate, but fault progression can increase repair cost over time.

Can you drive with P0078?

Most vehicles can be driven short-term with P0078, but postpone heavy load/highway driving until repaired.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

Repair obvious wiring/connector faults first to prevent repeat parts replacement.
Address the root fault mode (open) in the exhaust valve control circuit (bank 2) circuit/system.
Apply the required relearn/adaptation procedure if specified by service information.
Road-test and verify P0078 remains cleared under the conditions that originally set the code.

Fix options

Clear corrosion and protect terminals.
Restore continuity and verify pin tension.
Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$200-$900

Common mistakes when diagnosing P0078

Replacing parts without verifying voltage, ground, and signal integrity first.
Ignoring related stored/pending codes that indicate upstream faults.
Skipping post-repair verification drive cycle and readiness checks.

P0078 in common vehicles

P0078 appears across makes such as BMW, Mercedes-Benz, Audi, Volvo. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes P0078?

P0078 is commonly set by open faults affecting exhaust valve control circuit (bank 2).

How much does it cost to fix P0078?

For P0078, repair costs are typically $200-$900 depending on exact root cause, labor rates, and part quality.

Can I clear P0078 without repair?

You can clear P0078 temporarily, but the code usually returns until the underlying fault is corrected.