Allison 1000 & 2000 Gen 5 Fault Code:P0708 Transmission Range Sensor Circuit – High Input

CIRCUIT DESCRIPTION:
An Internal Mode Switch (IMS) is used by the TCM to detect the angular position of the shift selector shaft. There are five internal switches in the IMS: A, B, C, P, and NS. The TCM uses four of these switch inputs to determine the proper gear range that is selected. The fifth switch (NS), located in the IMS, is used as confirmation that the transmission is in neutral before the engine starter is engaged. DTC P0708 sets when the TCM detects an invalid switch condition and parity errors occur over consecutive ignition cycles.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM forces Variable Modulated Main off.
2. The diagnostic response is to shut all solenoids off, allowing the transmission to fault to hydraulic default “limp home”. Shift selector and hydraulic state of logic valves determines range.
3. DTC P0708 is stored in the TCM history.
4. The TCM inhibits Torque Converter Clutch (TCC) engagement.
5. Due to this failure and associated response, DTC P0722 can also set.
6. TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
The diagnostic tool may be used to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service information and therefore should not be used as a method to diagnose any transmission DTCs, function, or shift quality concern:

1. Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-39700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

Inspect the wiring for poor electrical connections at the TCM. Look for the following conditions:
1. A bent terminal.
2. A backed-out terminal.
3. A damaged terminal.
4. Poor terminal tension.
5. A chafed wire.
6. A broken wire inside the insulation.

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.

You may have to drive the vehicle in order to experience a fault.

NOTE: Due to the TCM logic used to detect and set P0708, this DTC can remain active even after an IMS replacement is complete and the ignition has been cycled. It is important to clear all active DTCs from the TCM after servicing the IMS.