Circuit Description
The installation of a transmission mounted park/neutral position (PNP) switch is required. This switch mounts directly onto the transmission housing from the outside, and detects the angular position of the shift selector shaft. This position is communicated to the transmission control module (TCM) so that certain vehicle control functions can be coordinated with the position of the shift controls. The PNP switch has redundant circuitry to alert the TCM in the event of a single wire or switch failure.
The neutral signal output of the PNP switch is typically used as confirmation that the transmission is in NEUTRAL before the engine starter is engaged. The PNP switch is interfaced to the starter circuit with weatherproof electrical connectors. The reverse signal provision may be used to activate vehicle back-up lights and/or reverse warning devices.
DTC P0708 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0708 Transmission Range (TR) Switch Circuit High Voltage
Conditions for Running the DTC
| • | 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. |
| • | DTC P0708 will be stored in TCM history. |
| • | The TCM freezes shift adapts. |
| • | 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
| • | 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. |
| • | If a P0875, previously a P1713, is shown in failure records as being set first on the failure list followed by a P0872, previously a P1711, combined with P0708, this generally indicates a PNP internal switch failure. Often when the DTCs are cleared they do not return, this may be due to moisture that was present at the time the DTC was set, causing a short internally. |
| • | Inspect the PNP switch linkage carefully for proper adjustment. Also, inspect the switch for signs of damage. |
Test Description
The numbers below refer to step numbers on the diagnostic table.
-
This step tests TCM input response.
-
This step tests the wiring harness for opens or shorts.
-
This step tests the wiring harness for a short to voltage.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 | Inspect for proper adjustment of the PNP switch. Refer to Park/Neutral Position Switch Adjustment and Shift Cable Adjustment . Is the PNP switch and 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 TR Sw. display? | -- | Go to Diagnostic Aids | Go to Step 4 |
Does each selected transmission range match the scan tool TR Sw. display? | PARK = 5 and 8 REVERSE = 5 and 4 NEUTRAL = 8 and 4 DRIVE 4 = 6 and 4 DRIVE 3 = 4, 5, 6, 8 DRIVE 2 = 5 and 6 DRIVE 1 = 6 and 8 | Go to Step 8 | Go to Step 5 | |
Using the DMM and the J 35616 GM terminal test kit measure the following:
Does the voltage measure within the specified value at all four terminals? | B+ | Go to Step 6 | Go to Step 7 | |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | |
7 | Test the signal circuits of the TR switch that did not indicate proper voltage for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
8 |
Important: A scan tool must be used in order to clear the code from TCM history. Replace the PNP switch. Refer to Park/Neutral Position Switch Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
9 |
Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM. Replace the TCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 10 | -- |
10 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK | Go to Step 1 |
