COVER 6B9885 - Caterpillar

Use this procedure to determine if the AT/MT/HT transmission interface relay (output 7) is operating correctly.Background InformationAllison AT/MT/HT transmissions require an input from the Engine Control Module (ECM) in order to regulate the transmission shifting. The ECM monitors various operating parameters in order to determine if the transmission should use closed throttle shift modulation or full throttle shift modulation. Programming the "Transmission Style" parameter to "AT/MT/HT Option1", to "AT/MT/HT Option2", to "AT/MT/HT Option3", or to "AT/MT/HT Option4" activates ECM output 7 in order to control a transmission interface relay that is connected to the Allison transmission. The ECM does not communicate with the Allison AT/MT/HT transmission via a data link.The "Transmission Style" parameter must be programmed to one of the AT/MT/HT options for output 7 to activate the AT/MT/HT transmission interface relay.Cruise Control or Vehicle Speed Limiting is InactiveOutput 7 is disabled if any of the following conditions occur:
The engine is not running.
The accelerator pedal position is less than 65 percent of the value of the "AT/MT/HT Part Throttle Shift Speed" parameter. Refer to the note below.Note: The "AT/MT/HT Part Throttle Shift Speed" parameter provides three different settings of shift modulation for the transmission. The "Low" setting disables the output below 65 percent throttle, the "Medium" setting disables the output below 55 percent throttle, and the "High" setting disables the output below 45 percent throttle.The transmission interface relay is enabled under any the following conditions:
The engine is running.
The accelerator pedal position is greater than 80 percent of the value of the "AT/MT/HT Part Throttle Shift Speed" parameter. Refer to the note below.Note: The "AT/MT/HT Part Throttle Shift Speed" parameter provides three different settings of shift modulation for the transmission. The "Low" setting enables the relay above 80 percent throttle, the "Medium" setting enables the relay above 70 percent throttle, and the "High" setting enables the relay above 60 percent throttle.Cruise Control or Vehicle Speed Limiting is ActiveOutput 7 is disabled if any of the following conditions occur:
The speed of the vehicle is greater than 2 km/h (1 mph) of the cruise set speed or the vehicle speed limit.
The load factor is less than 75 percent.
The engine speed is greater than 2000 rpm.The output is enabled when the load factor is greater than 98 percent.
Illustration 1 g00729187
Schematic for the AT/MT/HT transmission relay
Illustration 2 g01152517
Pin locations on ECM connector
(P1-20) Output 7 Test Step 1. Check Electrical Connectors and Wiring
Thoroughly inspect ECM connectors J1/P1 and the firewall bulkhead connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Perform a 45 N (10 lb) pull test on the wires that go to P1-20 and P1-12.
Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Check the harness and wiring for abrasion and for pinch points from the sensor to the ECM. Expected Result:All connectors, pins and sockets are completely coupled and/or inserted and the harness and the wiring are free of corrosion, of abrasion and of pinch points.Results:
Yes - The wiring is OK. Proceed to