Transmission Control System MIL Request Circuit/Open
The PCM has detected a problem in the malfunction indicator lamp circuit of automatic transmission control system. A code has been stored and the service engine light has failed to illuminate. A variety of different transmission failure codes will trigger this code being stored in the PCM. Some models will also place the transmission in “limp in” mode along with this code being stored.
Code Set Parameters
In order for this code to be exhibited, the automatic transmission control system must detect an abnormal reading from one or more of its many sensors, solenoids, and/or switches, store a code in the PCM, demand a malfunction indicator lamp be illuminated, and malfunction indicator lamp illumination must fail. Any malfunction which causes a specific transmission component or system failure code to be stored is capable of causing this code to be stored, as well.
Symptoms can range from none at all to total transmission failure that results in a stranded motorist condition. Some of the most common symptoms may include a lack of service engine soon lamp illumination, transmission slippage, transmission overheating, harsh shifting, failure to shift (up or down), or engine stall when coming to a stop.
The most common cause of this code is a defective malfunction indicator lamp bulb. Other causes include defective wiring and connectors.
Stored codes are frequently overlooked when this condition is exhibited simply because no service engine soon lamp is illuminated.
- A scanner (or code reader) and a digital volt/ohmmeter will be helpful when diagnosing this code.
Begin with a visual inspection of all wiring and connectors
- Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
- Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
- This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
- Continue by clearing the code and operating the vehicle to see if it returns
- This will help to determine whether or not the malfunction is intermittent
After the codes are cleared, test drive the vehicle to see if the code returns
- If the code fails to immediately return, you may have an intermittent condition
- Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can even be attempted
This code pertains to malfunction indicator lamp illumination, when a transmission fault is detected
- This type of code applies to vehicles with automatic transmissions only
- If this code is present in your vehicle that is equipped with a manual transmission, suspect a faulty PCM or programming error.
As an informational code only, the transmission control code does not actually isolate a particular transmission component or system failure
- When this code is stored it simply indicates that another (more specific) transmission code has been stored or a transmission problem has been detected
- The P0802 indicates that a transmission control code has been forwarded to the PCM (where it was stored) and service engine soon lamp illumination has failed.
While the majority of vehicles equipped with OBD-II diagnostic systems utilize a PCM, with the engine and transmission control systems integrated into one unit, some models use a separate engine control module (ECM) and transmission control module (TCM)
- When the TCM detects a fault from one of its many sensors, switches, or solenoids, it inputs a transmission control system code to the ECM
- Even when the engine and transmission control modules are integrated, some models use this code to activate malfunction indicator lamp illumination and initiate the transmission control limp-in mode
- In limp-in mode, electronic pressure modulation is bypassed so that maximum pump pressure can be maintained
- Maximum pump pressure is often required to allow the transmission to shift and pull
- Shifting will likely be harsh when the vehicle is in limp-in mode.
Continue your diagnosis of the transmission control system code by diagnosing and repairing all other stored transmission codes
- Chances are that once the other codes are repaired, this code will not return because it is an information code.
After the transmission control system codes are repaired, address the malfunction indicator request code by testing malfunction indicator lamp function
- The malfunction indicator lamp should be illuminated with the key on and the engine off
- If the malfunction indicator lamp is on with the key on and the engine off, suspect a defective PCM or programming error, faulty TCM, or CAN BUS malfunction.
If the malfunction indicator lamp fails to illuminate with the key on and the engine off, replace the malfunction indicator lamp bulb and retest its operation
- If the bulb still fails to illuminate, obtain a system wiring diagram, disconnect all related controllers, and use the digital volt/ohmmeter to perform a resistance and continuity test on all circuits
- Repair or replace shorted, open, or damaged circuits as required and retest the system to ensure a successful repair.