Allison 3000 & 4000 Gen 4 Fault Code: P0708 Transmission Range Sensor Circuit High Input (Strip Shift Selector)

DIAGNOSTIC RESPONSE:
Ignore defective strip selector inputs

CIRCUIT DESCRIPTION:
The 3000 and 4000 Product Family Transmission Control Module (TCM) can receive input from a strip-type shift selector. This type of shift selector communicates with the TCM via 4-bit parallel data wires. The strip shift selector button position determines the switch state (low or high voltage) of each parallel data wire. The TCM interprets each particular combination of switch states into a specific range selection, i.e. Reverse, Neutral, and Drive. The TCM sets DTC P0708 if the switch state of the four parallel data wires does not agree with a valid switch combination.

CONDITIONS FOR RUNNING THE DTC:
After TCM initializes normally and engine speed is above 200 rpm for more than 5 seconds.

CONDITIONS FOR SETTING THE DTC:
When the TCM detects an invalid parallel data message from a strip-type shift selector for greater than 1 second.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0708 is active, the following conditions occur:
1. The DTC is stored in the TCM history.
2. The TCM illuminates the CHECK TRANS light.
3. The TCM ignores input from the strip shift selector.
4. Locks in Neutral (N).

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
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:
This DTC may be caused by:
1. Short to power or short to another wire in W114, W138, W153, or W173.
2. High resistance or open in W114, W138, W153, or W173.
3. Poor vehicle grounds.
4. Unlocked connectors, expanded terminals, poor pin crimps or unlocked pins causing high resistance or open circuit.
5. Unlocked connectors, unlocked pins, causing short connectors.
6. TCM ground is at different voltage potential than the ground of the OEM voltage source responsible for strip shift selector.
7. Defective TCM.
8. Defective strip shift selector.

The PWM signal characteristics are shown below:

SS-1 (A) SS-2 (B) SS-4 (C) SS-Parity (E)
Button: R Sel Out: Reverse 173: Low 153: Low 114: Low 138: High
Button: N Sel Out: Neutral 173: Low 153: High 114: High 138: High
Button: D Sel Out: Drive-A 173: Low 153: Low 114: High 138: Low
Button: 3 Sel Out: Drive-B 173: High 153: Low 114: High 138: High
Button: 2 Sel Out: Drive-C 173: High 153: Low 114: Low 138: Low
Button: 1 Sel Out: Drive-D 173: High 153: High 114: Low 138: High