Error Code P0899 is defined as Transmission Control System MIL Request Circuit High. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to the present. This code appears in vehicles with transmission fluid temperature sensors. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

Error Code P0899 is set when the PCM (Powertrain Control Module) determines a problem communicating with the TCM (Transmission Control Module) through the MIL request circuit.

Common Symptoms

  • Engine light is on (service engine soon warning light)

Possible Causes

  • Defective transmission control module
  • Open or shorted harness in the TCM
  • Poor electrical connection in the TCM circuit

How to Check

First, check the stored code using an OBD-II scanner.

Next, check for burnt or shorted wirings in the TCM. Look for signs of damage in the TCM circuit and related wiring harness and connectors. Look for damaged components such as bent, broken, pushed out, or corroded pins.

How to Fix

  • Fix damaged, shorted, loose, or open wirings or connectors
  • Repair or replacement of TCM

This code could be tricky to properly diagnose and repair if you don’t have the right tools and experience. It is best to take your vehicle to a licensed technician to address the problem.