P0899 moderate

Transmission Control System MIL Request Circuit High

The P0899 code means the vehicle's onboard diagnostic system has detected: Transmission Control System MIL Request Circuit High. This is a moderate severity code.

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Keep driving?: Yes, but fix soon
DIY difficulty: hard
Estimated cost: $0 - diagnostic fee (pointer circuit; the real fault is usually a companion transmission code)

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LAUNCH CRP123X (Reads All Systems)

Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.

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Common Symptoms

Check Engine Light on
No symptom from this code itself - it reports the MIL-request line state

Probable Causes (Ranked by Likelihood)

Fault in the MIL-request circuit between TCM and ECM High
Wiring or connector damage Moderate
Module driver fault Low

Frequently Asked Questions

What does P0899 mean?

P0899 concerns the circuit the transmission controller uses to request the Check Engine Light - the signal itself is faulty (Transmission Control System MIL Request).

Can I keep driving with P0899?

Yes. This code is about the warning-light request line; check for companion transmission codes for anything that affects driving.

Mechanics Guide Step-by-step diagnosis

Step-by-Step Diagnostic Procedure

Read codes from BOTH the engine and transmission modules - the real fault usually lives in the TCM's own codes.
Diagnose any transmission codes found; repair, then clear both modules.
If no other codes exist, test the MIL-request circuit per the OEM diagram.

Sources 2

This page is built from documented references. Verify against your own service info before repair work.

SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition

Commonly Affected Vehicles

2010-2020 Ford F-150
2012-2019 Chevrolet Silverado
2011-2020 Toyota Camry
2009-2019 Honda Accord

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