P0802Transmission Control System MIL Request Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- On older vehicles with a separate transmission module and no MIL message on the CAN bus, the transmission module signals 'MIL on' over its own wire to the engine module. P0802 checks this wire for an open circuit. GM's Duramax tables of 2004 and 2005 (Allison 1000) describe it: at key-on the transmission module briefly pulls the line active like a bulb check; if the engine module sees no off-to-on transition between 0.125 and 7 s after ignition, the line is treated as open – type B, MIL after two trips. Only then is P0700 evaluated. The wire itself must be monitored because an open line would stop transmission emission faults from lighting the MIL. Newer vehicles send the request over CAN, where faults appear as U codes.
- What you may notice
- Check engine lamp on
- Transmission faults no longer light the MIL
- Usually no change in driving
- Likely causes
- LikelyMIL request wire or connector between the modules open or corroded
- PossibleTransmission module without power or ground (fuse, relay)
- RareModule output or input faulty
- RareWrong or retrofitted transmission module without this line
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.