Technical Description of OBD-II Trouble Code
Shift Timing Solenoid B Range/Performance
What does that signify?
This is a standard diagnostic trouble code (DTC) for transmission issues and is commonly found in OBD-II vehicles with automatic transmissions. It can be applicable to various vehicle makes such as Chevrolet / Chevy, Volvo, GMC, Saab, Subaru, VW, BMW, Toyota, Ford, Dodge, etc.
The shift timing solenoid is a crucial component that enables smooth shifting in an automatic transmission based on your driving requirements. The TCM (Transmission Control Module) monitors and controls the functionality of the solenoid.
The main function of the solenoid is to regulate the internal flow of hydraulic fluid (ATF: Automatic Transmission Fluid) to facilitate smooth shifting of the transmission. Essentially, these solenoids act as electro-mechanical “pistons”. In most cases, there are multiple shift timing solenoids in the system, and the specific solenoid can be identified by referring to the letter mentioned in the code, depending on the make and model of your vehicle.
The ECM (Engine Control Module) triggers the MIL (Malfunction Indicator Lamp) and displays the code P078B, along with associated codes (P078A, P078C, P078D, and P078E), when it detects one or more issues with the shift timing solenoid or its circuit. The circuit includes the TCM, which may be located in a volatile position depending on the model. There can be various potential causes, including mechanical and/or electrical factors, depending on the specific code and the presence of any other active codes. Automatic transmissions are complex systems, and it is advisable for non-experts or average DIYers to seek professional assistance, especially for internal transmission work.
The code P078B Shift Timing Solenoid B Range/Performance is set when the ECM (Engine Control Module) and/or the TCM (Transmission Control Module) detects that the solenoid is operating outside the expected range or abnormally.
What is the severity of this DTC?
I would classify this code as moderately severe. If left unresolved for an extended period, it can cause significant damage to the transmission, not to mention the financial implications.
What are some of the symptoms of the code?
The symptoms associated with a P078B trouble code may include:
What are some of the common causes of the code?
The potential causes for this P078B transmission code may include:
What are some P078B troubleshooting steps?
Prior to initiating the troubleshooting process for any malfunction, it is advisable to refer to the Technical Service Bulletins (TSB’s) specific to your vehicle’s year, model, and transmission. This step can save time and money during the diagnosis and repair process!
Basic Step #1
The first step is to check the ATF (Automatic Transmission Fluid). If the fluid appears dirty, has a burnt smell, is overfilled, or has an abnormal color, it may be time to change the fluid. If you have driven your vehicle for 30,000 to 60,000 miles (50,000 to 100,000 kilometers) without ever changing the fluid or keeping any records of it, not only could this be the cause of the issue, but it could have been prevented by following the recommended maintenance schedule. It’s worth considering! Old fluid is dirty fluid, and dirty fluid can lead to blockages, which in turn can trigger this code, so it is important to change the fluid!
NOTE: Follow the manufacturer’s recommended steps when checking ATF. This simple step can vary significantly between different makes and models.
Basic Step #2
If the fluid is in good condition, but the code is still active and symptoms persist, depending on your specific model, you may be able to access the shift solenoid externally. In such cases, inspect the solenoid and its harness/connectors for any signs of damage. Repair or replace any issues as necessary. It’s also a good time to check for any leaks!
TECH TIP: If your shift solenoid is internal, I do not recommend attempting to access it. Instead, explore other options. Diagnosing and repairing internal transmission issues should be left to a certified technician.
NOTE: The TCM and harnesses involved in this circuit may be exposed to harsh road conditions, so ensure that everything is intact and functioning properly.
Basic Step #3
Test the shift timing solenoid. There may be multiple ways to test the solenoid. One method involves conducting a resistance test using a multimeter to measure the resistance between the pins in the solenoid, which helps verify its electrical integrity to some extent. Another method involves manually applying voltage to the solenoid to verify its mechanical operation. The specific testing procedure should be specified in your manufacturer’s service manual or technical literature.
Basic Step #4
Test the circuit from the TCM. You may be able to verify the functionality of the sensor and its circuit by performing the same tests as mentioned above, but this time from the pins at the TCM and/or ECM. This is a useful technique to assess not only the integrity of the solenoid but also the electrical integrity of the circuit.
