P0802: Transmission Control System MIL Request Circuit/Open

What Does The P0802 Code Mean?

If your vehicle has stored a code P0802, it means that the powertrain control module (PCM) has received a data input signal indicating that the transmission control system (TCS) has detected a malfunction which requires malfunction indicator lamp (MIL) illumination.

The transmission control module (TCM) may be stand alone unit but is most commonly integrated into a single housing with the engine control module (ECM). This is what is referred to as the PCM.

The PCM utilizes input signals from multiple engine and transmission sensors to calculate automatic transmission shift strategy. A high pressure pump (inside the transmission) forces fluid through the valve body and into the sprag assembly; in addition to lubricating and cooling the transmission.

The high pressure fluid allows the clutches to separate from the sprag momentarily so that the gear ratio may be changed smoothly. One or more electronic pressure control (EPC) solenoids help to regulate fluid pressure. Electronic pressure (EP) sensors provide the PCM with pertinent data regarding fluid pressure at various points in the transmission.

Electronic shift solenoids are used to interrupt the flow of high pressure fluid so that the transmission shifts gears when commanded. The PCM uses voltage input signals from the transmission input speed sensor and transmission output speed sensor to determine if the transmission is shifting efficiently.

As with many other automatic transmission malfunctions, a transmission control system code may be caused by either an electrical or mechanical failure. If the PCM detects a malfunction which demands MIL illumination, a code P0802 will be stored and a MIL illuminated.

What Are The Symptoms Of The P0802 Code?

Symptoms of a P0802 trouble code may include:

• Erratic or harsh shifting
• Delayed or no gear engagement
• The transmission may be placed in limp-in mode

What Are The Potential Causes Of The P0802 Code?

Causes for this code may include:

• Defective TCM or PCM
• Shorted or open transmission control circuits
• Controller programming error

How Serious Is This P0802 Code?

A stored code P0802 indicates that a potentially serious TCS malfunction has been detected. Conditions which contributed to a code of this nature being stored should be rectified as quickly as possible.

How Can You Fix The P0802 Code?

When diagnosing automatic transmission codes, you should begin by making sure that the transmission fluid is clean and that the transmission if filled to the appropriate level. If the fluid level is low, locate the source of the leak and repair the condition. Refill the transmission with the recommended fluid and proceed.

If the fluid is excessively dark and smells strongly of burnt friction material, it will need to be replaced. This can be accomplished by removing the transmission pan (and draining the torque converter) or flushing the transmission (recommended).

Either way, you will want to replace the filter at this time too. When removing the pan from the transmission, take care to preserve whatever debris may have landed therein. If the pan is relatively clear of debris you can assume that the clutches are mechanically intact. If there is an excessive amount of friction material in the pan (and stuck to the magnet), the transmission will require a rebuild from a qualified technician.

A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of vehicle specific diagnostic information will be required to diagnose a code P0802.

You may use your source of vehicle information to locate a technical service bulletin (TSB) that matches the vehicle year, make, and model; as well as the engine size, code/s stored, and symptoms exhibited. If you find one, it could yield helpful diagnostic information.

With the transmission filled to the appropriate level with the recommended fluid, proceed with the first step of the diagnosis.

Step 1

Use the scanner (connected to the vehicle diagnostic connector) to retrieve all stored codes and pertinent freeze frame data. It is a good idea to write this information down before clearing the codes then test-drive the vehicle until the PCM either enters readiness mode or the code is reset.

If the PCM enters readiness mode at this time, the code is intermittent and may be much more difficult to diagnose. If this is the case, the conditions which contributed to the code being stored may need to worsen before an accurate diagnosis can be made.

Step 2

If the code is immediately reset, the next step of your diagnosis will require that you search your vehicle information source for diagnostic flow-charts, connector pin-out charts, connector face views, and component testing procedures/specifications.

Step 3

Use the DVOM to test voltage and ground circuits at the TCM/PCM. If voltage and ground are detected, use the DVOM to check controller output. Begin by testing components and sensors related to specific symptoms. Any components which fail to comply with recommended specifications should be considered defective.

Step 4

If no transmission control components have failed, use the DVOM to test system circuits. The voltage drop testing method works well for this task. Disconnect all controllers from the circuit prior to testing resistance with the DVOM.

Additional notes:

• Test TCM/PCM circuit fuses with the circuit loaded to avoid misdiagnosis

Recommended Parts

Below are some recommended auto parts to help you address the trouble code affecting your vehicle and get it running smoothly again:

>>> Twippo 372Pcs Waterproof Wire Connectors Kit
>>> TCM
>>> INNOVA 5210
>>> KAIWEETS Digital Multimeter

Note: During the purchasing process, please check carefully whether the part you want to buy fits your car!

Reference Sources

P0802 Transmission Control System MIL Request Circuit/Open, OBD-Codes.