P0899Transmission Control System MIL Request Circuit High
- 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
- The MIL request circuit is a dedicated wire over which the gearbox module asks the engine module to switch on the MIL. Today that request travels over CAN and shows as P0700 in the engine module; older Subarus, also sold as Saab 9-2X, used a single serial wire with its own codes P0864 to P0866. P0899 means the request wire stays high: an open line held up by the engine module's pull-up, a short to voltage or, with active-low logic, a gearbox module without power. No maker documents the code; Subaru's equivalent is P0866, set after more than 3 s high with MIL after two trips.
- What you may notice
- MIL on
- Gearbox faults may not be reported
- Limp mode as well if the gearbox module has no power
- Likely causes
- LikelyWire open (pull-up in the engine module)
- PossibleShort to voltage
- PossibleGearbox module without power or ground
- RareGearbox module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.