P0786 code definition
The P0786 trouble code detects an issue with the shift/timing solenoid
What the P0786 code means
The P0786 code is a generic OBD-II trouble code that signals a problem with the shift/timing solenoid. The shift solenoid is responsible for controlling the fluid transfer in between hydraulic circuits and, more importantly, for activating gear ratio changes in the automatic transmission. Gear ratios are chosen based on numerous factors such as engine speed and throttle position, and help increase the engine performance and the fuel economy of the vehicle. When the powertrain control module (PCM) detects that the desired gear ratio and the actual gear ratio are not matching, then the P0786 trouble code will be triggered.
What causes the P0786 code?
There are a handful of problems that can cause the P0786 trouble code to be detected:
- Defective shift solenoid
- Insufficient transmission fluid levels
- Dirty transmission fluid
- Hydraulic blockages within the internal transmission
- Damaged electrical components in the internal transmission
- Malfunctioning components in the internal transmission
- In rare cases, a defective PCM or transmission control module
What are the symptoms of the P0786 code?
The P0786 trouble code will often be accompanied by the Check Engine Light being illuminated on the dashboard. In addition, the vehicle may experience a number of transmission issues. These could include difficulty or inability to shift into a certain gear or out of a certain gear, rough shifting, slippage, and overheating. It is also common for the vehicle to have a noticeable decrease in fuel efficiency, and “limp-in” mode may be activated in the transmission.
How does a mechanic diagnose the P0786 code?
The P0786 trouble code will be diagnosed using a standard OBD-II trouble code scanner. A reputable mechanic should use the code scanner to observe the freeze frame data and gather information about the P0786 code. The technician will also look for any additional trouble codes that are present. Next, the trouble codes should be reset, and the vehicle will be restarted, to see if the codes return. If they do not, the issue is likely intermittent, or was erroneously detected.
If the P0786 code returns, the mechanic should begin by inspecting the transmission fluid. If the fluid level is low, or the fluid is slightly dirty, it should be handled, and leaks should be looked for. If the fluid is significantly contaminated, that suggests a larger issue with the transmission, and the entire system will need to be inspected, and possibly rebuilt or replaced.
After checking the fluids, the mechanic will visually inspect all of the electrical components in the internal transmission, to see if any wires are shorted, or any connectors are loose or damaged. All faulty electrical components will need to be replaced.
Next, the technician will inspect the shift solenoid, and then the hydraulic pumps and fluid lines (by using a pressure gauge). If the problem is still not found, then the entire internal transmission system will need to be inspected.
After any component is replaced, the trouble codes will need to be reset, and the vehicle should be restarted to see if the codes remain detected. This will allow the mechanic to know as soon as the issue has been resolved.
Common mistakes when diagnosing the P0786 code
The most common mistake that can be made in diagnosing the P0786 codes comes from a failure to adhere to the OBD-II trouble code diagnosis protocol. Following the protocol step by step is imperative, as it helps the mechanic identify and fix the issue in an efficient manner. It is common for shift solenoids to be replaced when a shift solenoid circuit is the issue. This happens when a mechanic fails to address the trouble codes in the order in which they appear, and therefore tries to fix the P0786 code without first addressing prior codes.
How serious is the P0786 code?
A vehicle with a detected P0786 code will likely still be able to drive, though it may have a very difficult time shifting, which will be noticeable to the driver. Continuing to drive with a detected P0786 code runs the risk of severely damaging the internal transmission, so the code should be inspected as soon as possible.
What repairs can fix the P0786 code?
Some repairs for the P0786 trouble code include:
- Replacement of shift solenoids
- Replacement of electrical components in the internal transmission
- Addition of transmission fluid
- Flushing transmission fluid
- Patching of leaks, and unblocking of hydraulic blockages
- In rare cases, replacement of the PCM
Additional comments for consideration regarding the P0786 code
The P0786 trouble code only applies to vehicles that have an automatic transmission.
This code will often be accompanied by other shift solenoid trouble codes.
Need help with a P0786 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.