P078A Shift Timing Solenoid B Malfunction
OBD-II Trouble Code Technical Description
Shift Timing Solenoid B Malfunction
What does that mean?
This is a generic transmission diagnostic trouble code (DTC) and typically applies to OBD-II vehicles equipped with an automatic transmission. Vehicle makes may include but aren't limited to Chevrolet / Chevy, Volvo, GMC, Saab, Subaru, VW, BMW, Toyota, Ford, Dodge, etc.
The shift timing solenoid is one of many components that allow an automatic transmission to shift seamlessly according to your driving needs. The TCM (Transmission Control Module) monitors and controls the solenoids functionality.
The solenoids main purpose is to control hydraulic (ATF:Automatic Transmission Fluid) flow internally to assist in shifting the transmission. Essentially these solenoids are electro-mechanical "pistons". Most times, their are many shift timing solenoids within the system so you may be able to refer to the letter included in the code to pinpoint which solenoid you are working with depending on your particular make and model.
The ECM (Engine Control Module) illuminates the MIL (Malfunction Indicator Lamp) with P078A and associated codes (P078B, P078C, P078D, and P078E) when it monitors one or more issues within the shift timing solenoid or it's circuit. The circuit includes the TCM which depending on the model could be in a volatile location. Their are many possible causes here so it could be either be mechanical and/or electrical depending on the code and if any others are active. Automatic transmissions are intricately designed systems and in my opinion, the layman or average DIYer should leave it to the pros here especially when it comes to internal transmission work.
The code P078A Shift Timing Solenoid B Malfunction is set there is a general malfunction present within the solenoid or its circuit.
What is the severity of this DTC?
I would say this code is moderately severe. If this issue is left unrectified for too long you could cause some serious harm to the transmission not to mention your pocketbook.
What are some of the symptoms of the code?
Symptoms of a P078A trouble code may include:
Stuck in gears Erratic shifting Transmission slippage Hard or harsh shifting Inefficient shift timing Poor driveability Poor acceleration Overall poor performanceWhat are some of the common causes of the code?
Causes for this P078A transmission code may include:
Damaged or defective shift timing solenoid Dirty Automatic Transmission Fluid (ATF) Low ATF Obstruction in ATF passages Broken or damaged wiring harness TCM issue ECM issue Pin/connector problem (corrosion, melting, broken lock tab etc.)What are some P078A troubleshooting steps?
Prior to beginning the troubleshooting process for any malfunction you should research the Technical Service Bulletins (TSB's) for the specific vehicle by year, model and transmission. This step can save you time and money during diagnosis and repair!
Basic Step #1
First thing i would do here is check the ATF (Automatic Transmission Fluid). If the fluid is dirty, smells burnt, overfilled and/or abnormal color it may be time to change your fluid. If you've owned your vehicle for 30,000 to 60,000 miles (50,000 to 100,000 kilometers) and don't remember ever changing your fluid or have any records of it, not only may this be your problem, but it may of been avoided by simply following your maintenance schedule. Just food for thought! Old fluid is dirty fluid, dirty fluid can cause blockages and blockages can cause this code so change your fluid!
NOTE: Follow manufacturers recommended steps when checking ATF. This simple step can vary a meaningful amount between makes and models.
Basic Step #2
Fluid is good, code is still active and symptoms present? Depending on your specific model, th
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