Sub ROM Unit

Installing location: The valve body upper part
Function: To obtain A/T fluid pressure stability by compensating for solenoid & valve body unit fluid pressure differential.
Principle: Install additional ROM onto valve body of automatic transmission and input fluid pressure differential of solenoid & valve body so that TCM reads the input data to perform fluid pressure compensation.

Fig 1: Identifying Sub ROM Unit In Valve Body
Courtesy of KIA MOTORS AMERICA, INC.

Fig 2: Sub ROM Unit Data Flow
Courtesy of KIA MOTORS AMERICA, INC.
Maintenance
1. When replacing with a new TCM in the vehicle
  - TCM automatically reads SUB ROM DATA during IG ON. At this time, shift range valve is off for about 2.5 second.
2. When replacing A/T (regardless of new or old ones) in the vehicle
  - Must erase SUB ROM DATA stored in TCM.
  - With the ignition ON (engine OFF), maintain 50% throttle opening in R range while using the TCU SUB ROM RESET mode on the scan tool.
  - TCM reads SUB ROM DATA from a new A/T upon IG ON again after IG OFF.
3. Moving TCM from vehicle A to another vehicle B
  - Perform the same way as in step 2.