The OBD2 code P0078 refers to “Exhaust Valve Control Solenoid Circuit High Bank 1,” highlighting an issue with the electrical circuit controlling the solenoid that manages the exhaust valve’s operation. This solenoid’s role is critical in optimizing the engine’s performance by adjusting the timing of exhaust valve opening and closing. Anomalies in this circuit can lead to engine inefficiency, rough idling, and power loss, as observed in various vehicle models.
P0078 quick overview
| Meaning | P0078: Exhaust Valve Control Solenoid Circuit High Bank 1 |
| Is it serious? | Yes, it can significantly affect the vehicle’s performance, leading to poor fuel economy and drivability issues. |
| Possible causes | – Faulty exhaust valve control solenoid – Damaged wiring harness or connectors – Incorrect oil flow to the solenoid – Problems with the engine control module (ECM) |
| How to diagnose? | Inspect wiring harness for damage or breaks. Test continuity and resistance in the solenoid circuit. Check for proper oil flow to the solenoid. Verify camshaft timing and solenoid operation. Inspect connectors and terminals for corrosion. Test MAF sensor functionality and verify ECM grounds. |
P0078 Meaning
When encountering the P0078 code, your car is signaling an electrical glitch in the system that controls when exhaust gases leave the engine. This system’s smooth operation is vital for your car’s power and efficiency.
Imagine trying to breathe with a stuffy nose; that’s how your car feels. The trouble might stem from simple issues like a bad wire or more complex ones like improper oil flow or a faulty solenoid. Addressing it promptly can restore your vehicle’s health, preventing further complications.
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How to fix P0078 – learn from mechanics
I looked into P0078 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Honda P0078
Vehicle information
Honda Accord, 2017, 2.4L engine
Issue + repair history
- Check engine light on intermittently
- Replaced exhaust valve control solenoid
- Replaced camshaft position sensor
- Symptoms include rough idling and loss of power
Other OBD2 Codes + Test Results
- P0078: Exhaust Valve Control Solenoid Circuit B1
- P0340: Camshaft Position Sensor Circuit Malfunction
- Live data shows erratic signal from exhaust valve control solenoid
Mechanic suggestions
- Inspect wiring harness for any damage or breaks
- Test continuity and resistance in the solenoid circuit
- Check for proper oil flow to the solenoid
- Verify camshaft timing
Final fix
Discovered damaged wiring harness near the exhaust valve control solenoid connector. Repaired wiring and cleared codes, issue resolved.
Case #2: Chevrolet P0078
Vehicle information
Chevrolet Silverado, 2015, 5.3L engine
Issue + repair history
- Check engine light stays on
- Replaced exhaust valve control solenoid
- Replaced engine control module (ECM)
- No noticeable improvement in performance
Other OBD2 Codes + Test Results
- P0078: Exhaust Valve Control Solenoid Circuit B1
- P0101: Mass Air Flow (MAF) Sensor Circuit Range/Performance
- Test results show low voltage at the solenoid
Mechanic suggestions
- Check for voltage supply to the solenoid
- Inspect connectors and terminals for corrosion
- Test MAF sensor functionality
- Verify ECM grounds
Final fix
Found corroded connector terminals at the exhaust valve control solenoid. Cleaned terminals and applied dielectric grease. Cleared codes and performed test drive, issue resolved.
Case #3: Toyota P0078
Vehicle information
Toyota Corolla, 2016, 1.8L engine
Issue + repair history
- Check engine light flashing
- Replaced exhaust valve control solenoid
- Replaced oxygen sensor
- Car hesitates during acceleration
Other OBD2 Codes + Test Results
- P0078: Exhaust Valve Control Solenoid Circuit B1
- P0135: Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
- Live data shows erratic readings from the solenoid
Mechanic suggestions
- Inspect wiring harness for any signs of damage
- Test continuity and resistance in the circuit
- Check for proper voltage supply to the solenoid
- Verify oxygen sensor functionality
Final fix
Discovered loose connection at the exhaust valve control solenoid connector. Secured connector and cleared codes, issue resolved.
How to diagnose P0078
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Brief Explanation |
|---|---|
| Inspect wiring harness and connectors | Checks for physical damage, wear, and disconnections that could interrupt circuit integrity. |
| Test continuity and resistance | Ensures electrical paths are clear and components are functioning within specification. |
| Check for proper oil flow to the solenoid | Verifies that the solenoid receives the necessary lubrication for operation. |
| Verify camshaft timing | Confirms that the engine’s timing aligns correctly for optimal performance. |
| Inspect connectors and terminals for corrosion | Looks for corrosion that might impede electrical flow and connectivity. |
| Test MAF sensor and verify ECM grounds | Ensures that the mass air flow sensor and ECM have proper grounding and functionality. |
| Check for voltage supply to the solenoid | Confirms that the solenoid receives the correct voltage needed for operation. |
| Verify oxygen sensor functionality | Checks if the oxygen sensor is accurately measuring exhaust gases for optimal engine performance. |
| Secure loose connections | Fixes any detected loose connectors to ensure stable electrical contacts. |
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko