The Allison automatic transmission MD 3060 is all electronic running off direct battery power to a series of relays, fuses and modules. The ECU (electronic control unit) for the transmission reads and controls inputs and outputs. Inputs include engine speed, output speed, turbine speed (the trans internal drive shaft) and throttle position. It computes these inputs into smooth shifts according to these variables.
The TPS Cable Complete - It's Located In The Engine Compartment Area
If it receives a bad signal everything goes to hell in a handbag. Code 21-16 is a trouble code for the Throttle Position Sensor. One of my newsletter subscribers from North Carolina has a 1996 Holiday Rambler motor home with a 5.9 Cummins diesel engine. He's dealing with this code and asked me to help him out.
The TPS control has 3 wires to it, one sends a 0 to 5 Volt signal to the ECU which regulates shifting patterns using these voltage readings. Full throttle and idle can be determined this way, if the wrong reading is sent then you will get a hard shifting scenario.The other 2 wires are the battery voltage and ground.
21-12 Code indicates that the ECU is receiving 14 counts or less. The TPS works with counts and 14 is too low so the problem might be at the closed throttle end of the TPS travel. The first check to make is the cable for frayed wires hanging up somewhere or a bad wire in the 3 wire harness.
My Crude Wiring Diagram Showing The Simplicity Of The TPS Circuit.
I've seen a couple of bad cables and have also replaced all three wires from the TPS to the Trans. ECU. You can check the wires for grounds, shorts or open circuits. If you replace the TPS you can reset it by cycling the ignition 5 times to reset the 0% and 100% throttle position or use the 'ProLink' Reader to reset the system.