P0899
Transmission Control System MIL Request Circuit High
Voltage on the transmission control system MIL request circuit is above the expected window. Wire shorted to B+ or driver open.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Common causes
Ordered by how often each turns out to be the cause.
- Wire shorted to B+Common
- Driver fault openPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- MIL Request Circuit
- TCM
P0899 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.