Transmission Control System MIL Request Circuit/Open
Code P0802 indicates the PCM has detected a malfunction in the transmission control system's MIL request circuit. This circuit is responsible for communicating transmission problems to the engine control module so the check engine light can be illuminated when needed.
What You Might Notice
- Check engine light illuminated
- Erratic or harsh shifting
- Delayed or no gear engagement
- Transmission entering limp mode
- Loss of transmission shift control
Most Common Causes
- 1
Defective TCM or PCM
The transmission control module or powertrain control module may have failed internally or have a software corruption that prevents proper MIL request circuit operation.
- 2
Shorted or open transmission control circuit
Wiring harness damage, connector corrosion, or broken connections between the TCM and PCM can prevent proper signal transmission in the MIL request circuit.
- 3
Corroded or damaged connectors
Poor electrical connections at the TCM or PCM connectors can cause intermittent or complete loss of communication in the MIL request circuit.
- 4
Ground or power distribution failure
Loss of proper ground or 12V power supply to the transmission control module can prevent the MIL request circuit from functioning correctly.
How to Diagnose It
- 1
Check Defective TCM or PCM — The transmission control module or powertrain control module may have failed internally or have a software corruption that prevents proper MIL request circuit operation.
- 2
Check Shorted or open transmission control circuit — Wiring harness damage, connector corrosion, or broken connections between the TCM and PCM can prevent proper signal transmission in the MIL request circuit.
- 3
Check Corroded or damaged connectors — Poor electrical connections at the TCM or PCM connectors can cause intermittent or complete loss of communication in the MIL request circuit.
- 4
Check Ground or power distribution failure — Loss of proper ground or 12V power supply to the transmission control module can prevent the MIL request circuit from functioning correctly.
How to Fix It
- 1
Inspect and repair wiring harness
Visually inspect all transmission control system wiring between the TCM and PCM for damaged insulation, breaks, or corrosion. Repair or replace any damaged wiring segments.
- 2
Clean or replace connectors
Disconnect and inspect TCM and PCM connectors for corrosion or loose pins. Clean with electrical contact cleaner or replace connectors if damaged.
- 3
Test and replace TCM if needed
Use a diagnostic scanner to verify TCM communication. If the TCM is unresponsive or fails diagnostics, it will need to be replaced and reprogrammed.
- 4
Replace PCM if required
If TCM tests normal but the MIL request circuit still fails diagnostics, the PCM may be faulty and require replacement and reprogramming.
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