In order to make the transmission shift properly, the TCM (transmission control module) has to communicate with a number of sensors and the ECU. If the data stream going to the ECU does not fall within the expected range preset in the controller software, a P0864 DTC will be saved.
How Serious is the Code?
A P0864 diagnostic trouble code is actually very serious, and can lead to a number of drivability issues.
Symptoms of a P0864 include:
- Delayed, harsh or erratic shifts
- Limp mode
- Shorted/frayed wiring
- Corroded/broken connectors
- Failed transmission control module
- Failed engine control module
- Software issues
How to Diagnose the Code?
Often, the cause of a P0864 OBDII trouble code is damaged wiring or a broken connector. Manufacturer TSB’s should also be checked for software updates and known module issues. If nothing is found, then the transmission control module and engine control unit should be suspected.
What Repairs Will Fix P0864?
- Repair or replace damaged wiring on the transmission wiring harness
- Replace or repair broken/corroded connectors
- Replace transmission control module
- Replace engine control unit
- Update TCM/ECU software
- P0865 – TCM Communication Circuit Low
P0866 – TCM Communication Circuit High