P0899 code meaning
Transmission Control System MIL Request Circuit High
Powertrain system Generic code P08xx codes Check engine light
What P0899 means
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.
P0899 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0899
- MIL on
- Gearbox faults may not be reported
- Limp mode as well if the gearbox module has no power
Common causes of P0899
- Most likelyWire open (pull-up in the engine module)
- PossibleShort to voltage
- PossibleGearbox module without power or ground
- Less likelyGearbox module faulty
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 moduleModule wiring
What each part of P0899 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. |
| 99 | The exact fault in that area. |
What to do next
- Note P0899 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 P0899
What does P0899 mean?
P0899 means "Transmission Control System MIL Request Circuit High". The MIL request circuit is a dedicated wire over which the gearbox module asks the engine module to switch on the MIL. It is a generic code, so it means the same on every make.
Is it safe to drive with P0899?
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 P0899 fail an emissions test?
Yes, it can. P0899 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 P0899 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will P0899 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.