P0078 code definition
Exhaust Valve Control Solenoid Circuit (Bank 1)
What the P0078 code means
P0078 is a generic OBD2 code indicating that the Engine Control Module (ECM) has tried to control the Bank 1 exhaust valve control solenoid, and found an issue present. This code may be seen in addition to P0079 and P0080.
What causes the P0078 code?
- An open or short in wiring
- Poor or faulty electrical connections
- Failed control valve solenoid
- Faulty ECM
What are the symptoms of the P0078 code?
How does a mechanic diagnose the P0078 code?
Hooks up a professional grade scan tool to the vehicle's OBD2 port to detect any codes present
Observes the freeze frame data to note the conditions of the car when the Check Engine Light was first illuminated
Clears the codes and performs a road test under the circumstances seen in the freeze frame data
If the code reappears during the test drive:
Performs a visual inspection for all wiring and connectors associated with the valve control circuit
Uses a scan tool to observe the data from the exhaust valve control solenoid and its changes over time
If the sensor is operating properly, then the manufacturer's test of the ECM should be performed.
Common mistakes when diagnosing the P0078 code
Any Check Engine Light can be easy to diagnose, or difficult due to intermittent issues and other factors. Following all steps in the proper order and not condemning any part until it is inspected and tested is the route to success. The most common mistake is replacing the solenoid before proper diagnosis is performed.
How serious is the P0078 code?
The P0078 code typically just elicits the Check Engine Light without any other adverse engine issues noticed. In the circumstances where the vehicle accelerates poorly or the fuel mileage suffers, this code should be diagnosed by a qualified technician as soon as possible to ensure safe driving and normal operation.
What repairs can fix the P0078 code?
- Repairing or replacing an open or short in wiring
- Replacing faulty exhaust valve control solenoid
- Replacing the ECM
- Correcting any connection issues
Additional comments for consideration regarding the P0078 code
The exhaust valve control solenoid plays an important factor in modern engines that have variable valve timing and is needed for proper operation of this system. Variable valve timing adds better fuel economy and aides in acceleration in vehicles equipped with it. Most modern engines use variable valve timing of some type.
A professional level scan tool that allows you to see the advanced sensor data such as live readings, sensor voltage, and sensor resistance is required to accurately diagnose this code.
Need help with a P0078 code?
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230 to have this issue resolved.
This article originally appeared on YourMechanic.com as P0078 OBD-II Trouble Code: Exhaust Valve Control Solenoid Circuit (Bank 1) and was authored by Spencer Clayton.