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.
- 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)
Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.
Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.
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What Are the Symptoms of P0899?
- Check Engine Light on
- No symptom from this code itself - it reports the MIL-request line state
What Causes P0899? (Most Likely First)
- Fault in the MIL-request circuit between TCM and ECM High
- Wiring or connector damage Moderate
- Module driver fault Low
Can I Still Drive with P0899?
Yes, but fix soon. P0899 is rated moderate severity. It is not an immediate stop-driving fault, but it will not clear itself — book the repair rather than ignoring the light.
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
How Do You Diagnose P0899?
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Read codes from BOTH the engine and transmission modules - the real fault usually lives in the TCM's own codes.
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Diagnose any transmission codes found; repair, then clear both modules.
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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
Which Vehicles Commonly Get P0899?
- 2010-2020 Ford F-150
- 2012-2019 Chevrolet Silverado
- 2011-2020 Toyota Camry
- 2009-2019 Honda Accord
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