P0899 Transmission Control System MIL Request Circuit High

P0899 points to a high transmission control system MIL request circuit. The MIL request path is stuck high, open, or above the expected range.

Code status

Needs verification

Not yet verified against SAE J2012_202509 / J2012DA. Treat unverified rows as a lookup aid, not repair authority.

System: Transmission
Scope: iso-sae-controlled-p0
Standard: SAE J2012 / ISO 15031-6
Source: legacy-import

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the transmission controller until the high MIL request circuit and related network data are tested.

Useful checks before replacing parts

Check MIL request circuit voltage, network request data, TCM communication, connector fit, open circuits, and short-to-voltage conditions.
Review companion transmission codes because the high request circuit may hide the original fault that requested the lamp.
Inspect module power, grounds, fuses, and wiring between the transmission controller and powertrain controller or network gateway.

Related OBD-II codes

These nearby transmission entries can help compare wording and fault area. They may share the same verification status as the source database.