Transmission Control System MIL Request Circuit/Open
The P0802 code indicates that the Transmission Control Module (TCM) has detected an open or short circuit in the MIL (Malfunction Indicator Lamp) request circuit. This circuit is used by the TCM to request the Powertrain Control Module (PCM) to illuminate the check engine light when a transmission-related fault is detected. An open circuit means the TCM cannot communicate the request to the PCM, so the MIL may not illuminate even when a transmission fault exists. This can lead to undetected transmission issues and potential drivability problems.
01. Most Common Causes
- Open or short circuit in the MIL request wire between TCM and PCM
- Faulty TCM (Transmission Control Module)
- Faulty PCM (Powertrain Control Module)
- Corroded or damaged connectors in the circuit
02. Symptoms You Will Notice
- Check Engine Light (MIL) may not illuminate when transmission fault is present
- Transmission may exhibit harsh shifting, slipping, or other abnormal behavior
- Possible limp mode activation
- Other transmission-related diagnostic trouble codes may be stored
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all stored codes and freeze frame data.
Step 2: Visually inspect the wiring and connectors between TCM and PCM for damage, corrosion, or loose connections.
Step 3: Test continuity and resistance of the MIL request circuit using a multimeter.
Step 4: Check for proper voltage and ground at the TCM and PCM connectors.
Step 5: If wiring is intact, perform a TCM and PCM communication test; replace faulty module if necessary.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code because the MIL may not illuminate, hiding other transmission faults that could lead to serious damage. Have the vehicle inspected as soon as possible.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair of wiring or connectors. If a module replacement is needed, costs can be higher.