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Error Code P0802 is defined as Transmission Control System MIL Request Circuit/Open. It is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made from 1996 up to present and equipped with automatic transmission. Specifications on the definition and steps for repairs may vary depending on the model and make of the vehicle.
This includes vehicles from, but not limited to, Chevrolet, Dodge, Ford, GMC, Kia, and Ram. Specifications on the definition, troubleshooting, and repairs, of course, vary between make, model, and powertrain configuration.
When Error Code P0802 appears, that means the PCM (powertrain control module) has detected a data input signal that shows a malfunction in the transmission control system (TCS), which also activates the malfunction indicator lamp (MIL).
The TCM (transmission control module) and TCCS may be stand-alone units. However, they are commonly integrated into a single housing with the ECM (engine control module), and this is what is usually referred to as PCM.
The PCM calculates the automatic transmission shift strategy by using input signals from multiple sources, such as the engine, transmission, and transfer case sensors. A high-pressure pump is equipped inside the transmission. The job of this pump is to force fluid through the valve body and into the sprag assembly, while also lubricate and cool the transmission at the same time. This high-pressure fluid allows the clutches to separate from sprag momentarily for a smooth gear ratio change. One (or more) electronic pressure control (EPC) solenoids help regulate fluid pressure. The Electronic Pressure (EP) sensors bring PCM the data about the fluid pressure at varying points in the transmission. These electronic shift solenoids are used to interrupt the flow of high-pressure fluid so that the transmission can shift gears when commanded. To determine if the transmission is shifting efficiently, the PCM uses voltage input signals from the transmission input speed sensors and transmission output speed sensors.
As with other codes related to an automatic transmission, a code for transmission control system may be caused by either electrical or mechanical failure. If the PCM determines a malfunction that demands the activation of MIL, then this code will be stored.
- Erratic or harsh shifting
- Delayed gear engagement
- No gear engagement
- Transmission may be in limp-mode
- Faulty PCM or TCM
- Shorted or open transmission control circuits
- A programming error in the controller
How to Check
Before diagnosing this code, make sure the fluid is clean, and the transfer case is filled to the appropriate level. If there is not enough fluid (level too low), then there must be a leak. Find the source of the leak and do the necessary repair. Then, refill the transfer case with the require fluid before proceeding with the diagnosis.
If the fluid is dark and smells strong of burnt friction material, then it must be completely replaced. You can remove the transmission pan to drain the torque converter or flush the transmission (recommended). You need to replace the filter as well.
When removing the pan from the transmission, preserve whatever debris may have landed therein. If the pan is clear of debris, then you can assume that the clutches are still mechanically intact. If there’s a lot of friction material present in your pant (and stuck to the magnet), you will have to take the vehicle to a qualified technician to rebuild the transmission.
Retrieve all stored codes and the pertinent freeze frame data by connecting the diagnostic scanner. You can write the information down before clearing the codes and take the vehicle for a test-drive until the PCM either enters readiness mode or the code is reset.
If the PCM sets to readiness mode, the code must be intermittent. This can be more difficult to diagnose, as the condition that caused the code may need to worsen before you can proceed with the diagnosis.
If the code immediately resets, however, then you can get to the next step. Read your vehicle information source and familiarize yourself with the diagnostic flow-chart. Locate the connector pin-out charts, connector face views, and the specifications for the component testing procedures.
Test the voltage and ground circuits at the TCCS controller by using the DVOM. If you can detect both voltage and ground, use the DVOM to check the controller output. Test the components and sensors related to the specific symptoms. Any components that fail to comply with the recommended specifications are probably defective.
If the TCCS components are in good condition, then test the system circuits using the DVOM. You can use the voltage drop testing method for this step. Make sure you disconnect all controllers before testing for the resistance with your DVOM.
How to Fix
- Replacement of TCM or PCM
- Repair or replacement of transmission control circuits
- Reprogramming of controller
This code is a serious problem. If the conditions that contributed to this code are present, then it should be addressed as soon as possible.
To avoid misdiagnosis, test the skip shift control circuit fuses with the circuit loaded.