Circuit Description
The transmission internal mode switch (IMS) is a sliding contact switch attached to the selector detent inside the transmission. The IMS is used by the transmission control module (TCM) to detect the angular position of the shift selector shaft. There are 5 internal switches in the IMS, A, B, C, P and NS. The TCM uses 4 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 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0708 Transmission Range (TR) Sensor Circuit High
Conditions for Running the DTC
| • | The components are powered and the ignition voltage is greater than 9.0 volts and less than 18 volts. |
| • | Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds. |
Conditions for Setting the DTC
DTC P0708 sets when the TCM detects an invalid condition and parity error occurring over consecutive ignition cycles.
Action Taken When the DTC Sets
While diagnostic response is active, one of the following conditions can occur:
| • | The TCM illuminates the malfunction indicator lamp (MIL). |
| • | The transmission fails to hydraulic default. |
| • | A shift to REVERSE will allow REVERSE range if DTC P0878 is not active. |
| • | DTC P0708 is stored in TCM history. |
| • | The TCM freezes shift adapts. |
| • | The TCM inhibits torque converter clutch (TCC) engagement. |
Conditions for Clearing the DTC
A scan tool must be used to clear the code from TCM history. This DTC does not automatically clear from TCM history after 40 ignition cycles.
Diagnostic Aids
Important: Due to the TCM logic used to detect and set DTC P0708, this code can remain active even after an IMS switch replacement is complete and the ignition has been cycled. Therefore, always clear all active DTCs from the TCM after servicing the IMS switch.
| • | Inspect the wiring for poor electrical connections at the TCM and powertrain control module (PCM). Inspect for the following conditions: |
| - | A bent terminal |
| - | A backed-out terminal |
| - | A damaged terminal |
| - | Poor terminal tension |
| - | A chafed wire |
| - | 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 condition. |
| • | Due to this failure and associated response, DTC P0722 can also set. |
| • | When monitoring "TR SW" while moving the selector through ranges, A/B/C/P states may indicate transitional states. Transitional states are the area between ranges. |
| • | TR SW A/B/C/P may indicate invalid states when selecting ranges. Invalid states confirm a concern is present. |
Test Description
The numbers below refer to step numbers on the diagnostic table.
-
This step tests TCM input response.
-
This step tests the integrity of the engine wiring harness.
-
This step tests the integrity of the transmission internal wiring harness.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 | Inspect the shift linkage for proper adjustment. Refer to Range Selector Lever Cable Adjustment . Is the shift linkage properly adjusted? | -- | Go to Step 3 | -- |
3 |
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data. Does each selected transmission range match the scan tool IMS display? | -- | Go to Diagnostic Aids | Go to Step 4 |
Does each IMS signal indicate OFF when grounded and ON when open? | A = terminal 73 B = terminal 53 C = terminal 14 P = terminal 34 | Go to Step 5 | Go to Step 10 | |
Does each IMS signal indicate OFF when grounded and ON when open? | -- | Go to Step 6 | Go to Step 7 | |
Does each IMS signal indicate OFF when grounded and ON when open? | -- | Go to Step 9 | Go to Step 8 | |
7 | Test the IMS circuit between the TCM and AT inline 20-way connector for an open or short to ground condition. Refer to Circuit Testing . Did you find and correct the condition? | -- | Go to Step 11 | -- |
8 | Replace the internal wiring harness. Refer to Wiring Harness Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
9 | Replace the internal mode switch. Refer to Transmission Internal Mode Switch Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
10 |
Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM. Replace the TCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- |
11 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 12 | Go to Step 2 |
12 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
