P0899Generic code

P0899 Code: Transmission Control System MIL Request Circuit High

The P0899 code means there is a fault, a high voltage signal, in the circuit the transmission computer uses to request the check engine light. The transmission works, but the driver may not get a warning. Wiring and communication are the usual culprits.

Severity
Low
Can I keep driving?
Yes, no immediate risk
Estimated cost
$5 to $300
Difficulty
Easy
System
Transmission
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0899 code means

The transmission computer asks the engine computer to turn on the check engine light through a dedicated line. The P0899 code means the voltage on that line is high. The transmission computer either controls the light directly or sends the request over the communication network.

On modern vehicles the fault is usually in the communication with the instrument cluster or the engine computer. On older ones it is a bulb or a wire.

Always begin with the simple things: the fuse, the relay and the connector. Then check supply, ground and signal with the component connected, using back probes, and finally the continuity of each wire to the computer. Only if all of that is good should you replace the component.

P0899 code symptoms

  • The warning light or indicator does not work.
  • Check engine light on.

Likely causes of the P0899 code

  1. Burnt-out bulb or LED on older vehicles.
  2. Wiring between the computer and the instrument cluster that is cut or shorted.
  3. Communication fault. Check for U codes.
  4. Instrument cluster with an internal fault.

How to diagnose the P0899 code step by step

  1. Watch the warning light self-test when you turn the key on.
  2. Check for communication codes.

How to fix the P0899 code

  • Repair the wiring, the bulb or the communication fault.

Technical reference data

  • When you turn the key on, the warning lights should come on for a few seconds.
  • Approximate values only: check the manufacturer data for your vehicle.

Brand-specific notes

On many vehicles you need a scan tool with access to the instrument cluster in order to diagnose this code, since a basic code reader cannot talk to that module.

Frequently asked questions about P0899

Can I drive with a P0899 code?
Yes. The transmission keeps working, but you may miss the warning if something else goes wrong with it.
Is it important?
The warning light exists to tell you about transmission faults, so it is worth fixing so you are not driving without that alert.
What usually fails?
The wiring or the communication between modules. On older vehicles, the bulb.
How much does it cost to fix P0899?
Between $5 and $300. A bulb or a wire repair is cheap, while a cluster repair costs more.
What does the P0899 code mean?
The P0899 code is a generic OBD2 code that means the circuit the transmission computer uses to request the check engine light is reading high.
Will a P0899 code clear itself?
Only if the cause was a temporary communication glitch. A broken wire or a bad bulb will keep it coming back.
What is the most common cause of P0899?
Damaged wiring or a communication fault between the transmission computer and the instrument cluster.

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