P0899
Generic (SAE) Basic entry
Transmission Control System MIL Request Circuit High
Severity
Medium
Typical repair cost
40 – 350 EUR
System
Powertrain
What it means
P0899 is stored when the engine control module measures a voltage in the Transmission Control System MIL Request circuit above the expected maximum, typically because the signal wire is shorted to battery voltage or the circuit is open and pulled up internally.
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Symptoms
- Check engine or transmission warning light
- Harsh, delayed or missing shifts
- Transmission stuck in one gear (limp mode)
- Shuddering or slipping under load
Common causes
- Damaged, chafed or corroded wiring in the Transmission Control System MIL Request circuit
- Corroded, loose or water-damaged connector terminals
- Failed Transmission Control System MIL Request component (sensor, solenoid or actuator)
- Poor ground connection for the module or component
- Faulty control module driver (rare, confirm all else first)
How to diagnose
- Read freeze frame data and note when the code set (cold start, under load, after rain)
- Inspect the Transmission Control System MIL Request connector for bent pins, corrosion and water; wiggle the harness with the engine running and watch live data
- Measure supply voltage and ground at the connector with the key on
- Check the signal wire for shorts to ground or battery and for continuity to the control module
- Test or substitute the Transmission Control System MIL Request only after wiring and connectors are confirmed good
- Clear the code and complete a drive cycle to confirm the repair
Frequently asked questions
Can I keep driving with P0899?
Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.
Will clearing P0899 fix it?
No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.