GM Service Manual Online
For 1990-2009 cars only

Object Number: 1746986  Size: LF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Control Module References

Circuit Description

The transmission adaptive pressure (TAP) Shift system allows the driver to manually shift gears by using the TAP Shift switches located on the Automatic Transmission Shifter. Pushing the Up switch will command an upshift and pushing the Down switch will command a downshift. The TAP Shift system is activated when the gear selector is in the D3 position and is deactivated in all other positions.

If the transmission control module (TCM) detects TAP enable switch Inactive and the TR switch indicates D3, DTC P1877 sets. DTC P1877 is a type C DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1877 Up and Down Shift Switch Performance - Range Switch in D3

Conditions for Running the DTC

    • No transmission range switch DTC P0705.
    • No TAP system DTCs P0815, P0816 or P0826.
    • No PSA DTCs P1810, P1816, or P1818.
    • No TAP system performance DTC 1876.
    • No communication DTC U0100.
    • The engine run time is greater than 5 seconds.

Conditions for Setting the DTC

The TCM detects the TAP enable switch is Inactive and the TR switch is D3 for 60 seconds.

Action Taken When the DTC Sets

    • The TCM does not illuminate the malfunction indicator lamp (MIL).
    • The TCM disables TAP Shift operation.
    • The TCM commands an alternate coast shift pattern where downshifts occur at higher vehicle speeds while coasting.
    • The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information a Failure Record.
    • The TCM stores DTC P1877 in TCM history.

Conditions for Clearing the DTC

    • A scan tool can clear the DTC.
    • The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non emission related diagnostic fault occurring.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Important: Before clearing the DTC, use the scan tool in order to record the Failure Records. Using the Clear DTC Information function erases the Failure Records from the TCM.

  4. Record the DTC Failure Records.
  5. Clear the DTC.
  6. Start the engine.
  7. Move the A/T shift lever to the D3 position.
  8. Select TR Switch on the scan tool.

Does the scan tool TR Sw. parameter display Drive 3?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Select TR Sw. A/B/C/P on the scan tool.
  2. Place the gear select lever in the D3 position.

Does the TR Sw. A/B/C/P display indicate the specified value for D3 range?

Low/Low/Low/Low

Go to Step 13

Go to Step 4

4

  1. Inspect the transmission linkage from the range selector to the manual shift shaft for proper adjustment.
  2. Adjust the linkage as necessary. Refer to Shift Control Cable Adjustment .

Did the linkage require adjustment?

--

Go to Step 21

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the TR Sw. connector. Additional DTCs may set.
  3. Turn ON the ignition, with the engine OFF.
  4. Select TR Sw. A/B/C/P on the scan tool.

Does the scan tool TR Sw. A/B/C/P display the specified value?

HI/HI/HI/HI

Go to Step 6

Go to Step 10

6

  1. Turn ON the ignition, with the engine OFF.
  2. Using the DMM and the J 35616 GM terminal test kit, measure the voltage at the Park/Neutral Position Switch (TR) signal A circuit. Refer to Measuring Voltage .
  3. Measure the voltage at the TR signal B.
  4. Measure the voltage at the TR signal C.
  5. Measure the voltage at the TR signal P.

Did you measure ignition voltage at all four terminals?

--

Go to Step 7

Go to Step 11

7

Install a fused jumper wire from the TR signal A circuit of the Park/Neutral Position Switch connector to ground while monitoring the scan tool TR Sw. A/B/C/P display. Refer to Circuit Testing and Wiring Repairs .

When the TR signal A circuit is grounded, do any other circuits indicate LOW?

--

Go to Step 12

Go to Step 8

8

Install a fused jumper wire from the TR signal B circuit of the Park/Neutral Position Switch connector to ground while monitoring the scan tool TR Sw. A/B/C/P display. Refer to Circuit Testing and Wiring Repairs .

When the TR signal B circuit is grounded, do any other circuits indicate LOW?

--

Go to Step 12

Go to Step 9

9

Install a fused jumper wire from the TR signal C circuit of the Park/Neutral Position Switch connector to ground while monitoring the scan tool TR Sw. A/B/C/P display. Refer to Circuit Testing and Wiring Repairs .

When the TR signal C circuit is grounded, do any other circuits indicate LOW?

--

Go to Step 12

Go to Step 19

10

Test the TR signal circuits of the TR switch assembly that did not indicate HI for a short to ground between the TCM connector and the Park/Neutral Position Switch connector. Refer to Testing for Short to Ground and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

11

Test the TR signal circuits of the Park/Neutral Position Switch Assembly that did not indicate ignition voltage for an open between the TCM connector and the Park/Neutral Position Switch connector. Refer to Testing for Continuity and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

12

Test the affected signal circuits of the Park/Neutral Position switch assembly for a shorted together condition between the TCM connector and the Park/Neutral Position Switch connector. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

13

  1. Select Drive Shift Request on the scan tool.
  2. Move the gear select lever in and out of the D3 position.

Does the scan tool Driver Shift Request display indicate the change?

Active/Inactive

Testing for Intermittent Conditions and Poor Connections

Go to Step 14

14

  1. Disconnect the A/T Shift Program Switch connector.
  2. Using Test Light check TUTD Enable Signal circuit for an Open or Short to Ground condition. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 15

15

Using Test Light check TUTD Enable Signal Ground circuit for an Open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 21

Go to Step 16

16

Using a DMM check across the Tap Enable switch circuit while moving the gear select lever in and out of the D3 position.

Did the Tap Enable Switch open and close as expected on the DMM?

--

Go to Step 17

Go to Step 18

17

Replace the BCM.

Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 21

--

18

Replace the A/T Shift Program Switch. Refer to Automatic Transmission Shift Lock Control Actuator Replacement .

Did you complete the replacement?

--

Go to Step 21

--

19

Replace the Park/Neutral Position Switch assembly. Refer to Park/Neutral Position Switch Replacement .

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the TCM.

Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 21

--

21

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Start the engine.
  4. Place the A/T Shift Lever in the Manual position.
  5. Select Specific DTC.
  6. Enter DTC P1877.

Has the test run and passed?

--

Go to Step 22

Go to Step 2

22

With a scan tool, observe the stored information, capture info and DTC info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK