Auto Gear Box Control Unit
The auto gear box control unit operates the solenoid valves in the automatic transmission to provide automatic control of gear shifts and torque converter lock-up. The auto gear box control unit is attached to a bracket which is secured to the cabin floor below the left front seat under a Black metal bracket.
A 75-pin connector links the auto gear box control unit to the vehicle wiring. Software in the auto gear box control unit monitors hard wired inputs and exchanges information with the ECM on a Controller Area Network (CAN) bus to determine gear shift and torque converter lock-up requirements. See Fig 1. Resultant control signals are then output to the automatic transmission solenoid valves.
The CAN bus, introduced on 1999 model year vehicles, provides the communication link between the ECM and the auto gear box control unit. Inputs and outputs to and from each control unit are transmitted via 2 twisted wire connections, CAN high and CAN low.
The CAN bus allows more engine data to be passed to the auto gear box control unit which, on earlier vehicles, would require a number of additional hardwired connections.
The CAN bus, introduced on 1999 model year gas vehicles, provides the communication link between ECM and TCM. Inputs and outputs to and from each control module are transmitted via 2 twisted wire connections, CAN high and CAN low. CAN bus allows more engine data to be passed to TCM which, on earlier vehicles, would require a number of additional hard wired connections. Additional engine data is used by TCM to give improved transmission quality and allows TCM to operate in a greater number of default modes in the event of sensor failure. Inputs and outputs on CAN communication bus are listed as follows. Inputs from ECM:
- CAN version identifier.
- Emissions (OBDII) control.
- Engine IAT.
- Engine speed.
- Engine speed fault flag.
- ECT.
- Engine torque.
- Engine torque fault flag.
- Friction torque.
- Maximum engine torque.
- Reduced engine torque.
- Road speed.
- Status of engine speed torque reduction.
- Throttle position.
- Calculated gear.
- Diagnostic information.
- Emission (OBDII) fault status.
- Engine torque reduction request.
- Gear position switch information.
- Output shaft speed.
- Mode information.
- Shift information.
- TCC lock-up solenoid.
If during a jump start, normal operating voltage is exceeded, transmission will be set to limp home mode and output for solenoid valve and pressure regulator will be switched off. Normal auto gear box control unit operating voltage is 9.0-16.0 volts. The auto gear box control unit can withstand an overcharge of 16.0-24.0 volts for one minute at 104 F° (40 C°) and a negative charge of down to -14.0 volts for one minute at 77 F° (25 C°) without sustaining damage. If voltage happens to drop to 6.5-9.0 volts, auto gear box control unit will run diagnostic checks on itself and CAN-Bus communication system. Also at this voltage, output for solenoid valves and pressure regulator will be switched off. At 3.0-6.5 volts auto gear box control unit will still retain data, but communication over CAN-Bus line will become unreliable and limp home mode will be activated. At 3 volts and under, system will not function.