P0899 Fault Code

Transmission Control System MIL Request Circuit High

• What does that mean?
• Symptoms
• Causes
• Solutions

The P0899 fault code indicates a problem with the Transmission Control System, specifically pertaining to the MIL (Malfunction Indicator Lamp) request circuit being high. This circuit is responsible for notifying the engine control unit (ECU) when a transmission issue arises, ensuring that the driver is aware of potential problems.

What are the symptoms of the P0899 code?

Symptoms associated with the P0899 code can vary, but may include:

• The check engine light being illuminated on the dashboard
• Erratic shifting or poor transmission performance
• Transmission slipping or harsh shifts
• Reduced power output from the engine
• The vehicle entering 'limp mode' which limits speed and performance to protect the transmission

What causes the P0899 code?

Common causes of the P0899 code include:

• Faulty transmission control module (TCM)
• Short circuits or open circuits in the MIL request circuit
• Damaged wiring or connectors affecting the transmission system
• Faulty transmission sensors that send incorrect signals
• Software issues in the TCM that may need an update or reprogramming

How to fix P0899?

To resolve the P0899 code, the following steps should be taken:

• Begin with a thorough diagnostic scan to confirm the P0899 code and inspect for any related codes.
• Visually inspect the wiring and connectors related to the transmission control system for any signs of damage or corrosion.
• Test the TCM and associated sensors for proper operation.
• Repair or replace any damaged wiring or connectors as needed.
• If necessary, reprogram or replace the TCM, using updated software if applicable.
• Clear the fault code and take the vehicle for a test drive to ensure the issue has been resolved.