A network of wires and connectors between the transmission control module and the engine control unit, allow the two computers to exchange data about what’s going on. If the ECU cannot communicate with the TCM, the transmission will not be able to shift properly. If there is an unusually high-voltage signal along this communication circuit, a P0899 DTC will be saved.
How Serious is the Code?
If the ECU does not know what the transmission is doing, it won’t be able to calculate the correct shift patterns to meet the driving conditions. When this happens, you will experience a number of drivability issues including slipping, failure to shift and engine stalling. So a P0899 diagnostic trouble code is actually pretty serious.
Symptoms of a P0899 include:
- Harsh shifts
- Slipping between gears
- Failure to upshift/downshift
- Engine stalls when you come to a stop
- Transmission overheats
- Wiring and/or connector damage
- TCM failure
- ECU software issues
- Failed ECU
How to Diagnose the Code?
Since the flow of information between the control modules and sensors are vital to your transmission’s operation, diagnosing a P0899 OBDII trouble code may be more electrical/electronic in nature. One of the best ways to start is to check the manufacturer’s TSB database to see if there’s any known causes and remedies for this OBD2 fault code. Software updates for the ECU may also solve the problem. Should nothing be found, the wiring and connectors should be carefully checked for signs of broken wires, loose connector pins and corrosion. The vehicle’s CAN BUS system may also need to be troubleshot.
What Repairs Will Fix P0899?
- Repair or replace damaged wiring/connectors
- Replace transmission control module
- Reprogram or replace ECU