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Error Code P0078: What It Means & What To Do?

OBD Code P0078 - Exhaust Valve Control Solenoid Circuit B1

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The P0078 fault code is defined as Exhaust Valve Control Solenoid Circuit Bank 1. It is a generic code indicates that the engine control module has tried to control the Bank 1 exhaust valve control solenoid and at the same time has found some issue. You can see this code in addition to P0079 and P0080 codes.

Learn More about OBD Error Code P0078

Oil pressure as well as an electrical solenoid is used by the exhaust valve control solenoid to control the position of the exhaust valve. The vehicles which are new are well equipped with variable valve timing. The opening and closing of the exhaust valve is adjusted by the engine control module with a motive of improving fuel consumption and at the same time would make sure to provide performance to the driver. The PCM would set the P0078 fault code if it determines that there is some issue with the exhaust control solenoid.


What causes this problem with the Exhaust Valve Control Solenoid Circuit B1?


  • There can be some faults in the exhaust valve timing control magnet retarder
  • You may experience some issues with the VT solenoid valve like there can be an open circuit in the solenoid coil.
  • There can be an open or short in wiring
  • Some sort of faults in the engine control module or powertrain control module
  • The car engine may not start
  • The engine oil level/pressure may be low
  • The electrical wiring may be loosened up or the connectors in the VVT circuit might be corroded
  • The issue of short to ground

Replace/Repair These Parts To Fix OBD Code P0078

  1. Valve Timing Solenoid - OBD Error Code P0078 can simply be due to faulty Valve Timing Solenoid. Replace old and damage components now!
  2. Engine Control Module - If there is any fault detected in the Engine Control Module, it will flash OBD Code P0078. Replace faulty ECM components now!
  3. Exhaust Valve Control Solenoid - OBD Code P0078 can flash if the Exhaust Valve Control Solenoid is damaged. You must replace it with a brand new one online with us.
  4. Powertrain Control Module - Did your mechanic just found out that there is some fault in the Powertrain Control Module? Buy top notch PCM parts from us at economical prices.

Symptoms Of OBD Error Code P0078

You might be thinking that how would you diagnose these problems? We at Parts Avatar Canada would help you diagnose the major symptoms easily. The P0078 would start producing a check engine light on the dash and would likely cause:


Common Symptoms


  • Check engine light may start illuminating
  • The car engine may suffer choppy acceleration and poor cruising fuel economy
  • Engine may not start functioning
  • The car engine will usually run fine, but you may start noticing rough idle
  • The overall engine performance
  • Warning light of service engine soon may start appearing

How To Correct P0078 Exhaust Valve Control Solenoid Circuit (Bank 1)

  • The car battery may be disconnected. If you want to access the module, then you must remove the trim panels
  • Then you must disconnect the engine control module connections to remove the module
  • Now the new module should be installed as well as secured. After that the electrical connections should be connected
  • Reconnect the battery and then connect the charger to maintain the battery charge if needed. Reinstall the removed access or trim panels
  • Program the engine control module to work with the vehicle for operation with an approved scan tool or methods
  • Disconnect the charger and road test the vehicle for proper operation

However, if you face any issue then you must visit us. We have stocked a wide range of best priced ECM, solenoid, check valve and a lot more to help you out in fixing your car.

Easy Diagnosis Of Engine Error OBD Code P0078

  • First of all, you must check for unplugged harness connections, look if there is any corrosion or some loose wires to connectors. The harness connectors from Solenoid and PCM should be unplugged, using a wiring diagram locate the + and - wires to the solenoid. The solenoid can be ground side or power side controlled; it all depends upon the application.
  • If you want to determine the power flow in the circuit, then you can check with factory wiring diagrams. Using a digital volt ohm meter (DVOM) set to the ohms setting, check for resistance between each end of the wire. An over limit reading on the DVOM may be an open in the wiring, loose connection or terminal.
  • Make sure that the resistance should be around 1 ohm or less, if there is excessive resistance there may be corrosion or bad wiring between the solenoid and the power control module or the engine control module.
  • Now with the electrical harness to the solenoid unplugged, using the DVOM set to ohms, you should check for resistance between each of the electrical terminals on the control solenoid itself.
  • You can use the factory specifications or a known good control solenoid if available to determine if there is excessive resistance in the solenoid. If there is an over limit or excessive resistance reading on the DVOM, then it means that there are some faults in the solenoid
  • Check for a short to ground through the control solenoid by putting either DVOM lead to a known good ground and the other to each terminal on the control solenoid. If there is resistance present, the solenoid may be shorted internally.
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made. Carefully inspect the electrical wiring and connectors for inconsistencies, including shorted or broken wiring and corroded connector faces
  • All the timing components should be properly aligned and that engine oil level and engine oil pressure should be within acceptable specifications
  • If all these checks are acceptable, then you must test the system components and voltage/resistance with the help of manufacturer’s reference voltage and resistance figures


Common Mistakes When Diagnosing the P0078 Code


The intermittent issues as well as many other factors play a very important role while diagnosing a check engine light. You must follow all the steps mentioned above in proper order and should not hurry in getting any car part replaced without getting it inspected properly and then you will surely be able to correct the issue. The most common mistake which people make is by replacing the solenoid before performing proper diagnosis.

Other Diagnostic Codes Related To OBD Code P0078

P0079 - Exhaust Valve Control Solenoid Circuit Low (Bank 1)

P0080 - Exhaust Valve Control Solenoid Circuit High (Bank 1)

P0027 - Exhaust Valve Control Solenoid Circuit Range/Performance Bank 1