Error Code P0702 Transmission Control System Electrical. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. This includes vehicle models from but not limited to Ford, Honda, Mazda, Mercedes Benz, Volkswagen, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model, and powertrain configuration.
If the vehicle shows up this error code, this means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has determined a problem in the electrical part of the TCM (transmission control system). This type of code is exclusive to vehicles with automatic transmission.
OBD-equipped vehicles control the automatic transmission electronically. This includes a control module, CAN (controller area network), multiple sensors and solenoids, a powerful hydraulic pump, and a hydraulic valve body, which are all extremely important for the electronically controlled transmission.
The transmission controller gets its input voltage signal from the sensors of both engine and transmissions. Engine sensor inputs include (but not limited to) engine RPM, throttle, angle, coolant temperature, and load percentage. Transmission sensor input, on the other hand, monitors the transmission input speed (RPM), transmission output speed (RPM), pump pressure, vehicle speed, shifter position, transmission temperature, torque converter lock-up percentage, and more. With this, the transmission controller uses input signals from the map shift strategy and electronic pump pressure parameters. The transmission controller then uses these input signals to map shift strategy and electronic pump pressure parameters. The job of the electronic pressure control valve is to regulate the pump pressure and help keep the transmission shift smoothly. If maximum pump pressure were applied directly to the valve body, shifting could instantly become harsh and could lead to serious damages to the driveline. Electronically-controlled solenoids work with spring-loaded ball valves, restricting and releasing high-pressure fluid through the hydraulic circuits. This causes up and downshifts as desired. However, another solenoid controls the percentage of torque converter lock-up, increasing fuel efficiency and power to the pavement.
CAN is actually a complex system of connectors and wires used to transmit data from the TCM (where applicable) to the PCM. The data (this includes stored codes) may also be shared with another controller through CAN. Transmission input and output speeds (RPM), transmission temperature, and vehicle speed are all shared between different controllers. This data is then used for comparison for various systems, including electronic traction control systems, anti-lock braking systems, and electronic stability control systems, etc.
Error Code P0702 is usually only stored if other electrical control codes are present.
If Error Code P0701 is stored, then harsh shifting in the transmission may be noticed. This is due to TCM being in limp-in mode. In which case, transmission pump pressure is increased dramatically, which is dangerous in the long run. Other common symptoms include:
- Failure of the transmission to shift
- Transmission fails to shift at all
- Increase in fuel consumption
Other transmission related codes may be present as well.
There are many possible causes for this code, some include:
- Transmission sensor failure
- Open or shorted circuits in the TCM
- Defective transmission controller
- Defective or programming error in PCM
How to Check
As with most codes, checking with a TSB (technical service bulletin) is a good starting point to diagnose this code. Other things you need include the basics, such as a scanner, DVOM (digital volt/ohmmeter), transmission gauge, and vehicle service manual (or equivalent).
Start the diagnosis with a visual inspection of the wirings and connectors in the transmission control. Repair or replace as necessary. Also, make sure check the battery, including the battery cables and terminal ends.
Then, connect the scanner to the vehicle diagnostic connector and retrieve all stored codes, including their freeze frame data. Take note of this information. Clear the codes and take the vehicle for a test drive.
If the code comes back immediately, then return to the recorded freeze frame data. Next, proceed on diagnosing and repairing all other codes present before attempting to diagnose Error Code P0702.
How to Fix
Error Code P0702 is an informational code for more specific problems. Dealing with the other codes first can usually clear other codes. If the code comes back after all other transmission problems (error codes) have been fixed, then the mechanic can attempt other repairs, such as:
- Repair or replacement of any damaged connectors, components, and wirings
- Rebuilding of the transmission (fluid flush and replacement of torque converter if the transmission has suffered extreme damage due to low fluid condition that was allowed for too long)
- Aside from low fluid condition, the transmission must be fixed off of leaks and filled with the appropriate amount
- Replacement of defective sensor, switches, and solenoids
- Replacement of hydraulic pump (if this proves to be the problem)
- Replacement of faulty PCM (or if this code is stored in a vehicle with manual transmission)
If ignored, this code can lead to catastrophic damage to the transmission, especially if it’s caused by the low fluid condition.
Make sure other transmission-related codes are addressed first before attempting to diagnose and repair this code since this code is usually associated with other transmission-related codes.