P0802 code meaning
Transmission Control System MIL Request Circuit/Open
Powertrain system Generic code P08xx codes Check engine light
What P0802 means
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.
P0802 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of P0802
- Check engine lamp on
- Transmission faults no longer light the MIL
- Usually no change in driving
Common causes of P0802
- Most likelyMIL request wire or connector between the modules open or corroded
- PossibleTransmission module without power or ground (fuse, relay)
- Less likelyModule output or input faulty
- Less likelyWrong or retrofitted transmission module without this line
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transmission control moduleEngine control moduleMIL request wiring
What each part of P0802 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 8 | Area: transmission. |
| 02 | The exact fault in that area. |
What to do next
- Note P0802 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0802
What does P0802 mean?
P0802 means "Transmission Control System MIL Request Circuit/Open". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0802?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0802 fail an emissions test?
Yes, it can. P0802 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0802 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0802 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.