For 1990-2009 cars

### Circuit Description

The TAP Shift system allows the driver to manually shift gears by using the Upshift and Downshift positions located on the automatic transmission shift Lever. Pushing the lever to the Upshift position will command an upshift and pushing the lever to the Downshift position will command a downshift. The TAP Shift system is activated when the gear selector is in the manual, M, position and is deactivated in all other positions.

If the transmission control module (TCM) detects TAP enable switch Active and the IMS does not indicate D5, DTC P1876 sets. DTC P1876 is a type C DTC.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC 1876 Up and Down Shift Switch Performance - Range Switch Not in D3.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1876 Up and Down Shift Switch Performance - Range Switch Not in D3

### Conditions for Running the DTC

• | Ignition voltage is between 8-18 volts.

• | The engine speed is between 450-6,800 RPM for 5 seconds.

• | No CAN errors present.

• | No TAP system DTCs P0815, P0816 or P0826.

• | No IMS range DTCs P1815, P1820, P1822, P1823, P1825 or P1826.

### Conditions for Setting the DTC

The TCM detects the TAP enable switch is Active and the IMS range is not D5 and it occurs at least 5 times in 12 seconds.

### Action Taken When the DTC Sets

• | The TCM does not request the engine control module to illuminate the malfunction indicator lamp (MIL).

• | The TCM disables TAP Shift operation.

• | 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 P1876 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.

• | The TCM cancels the DTC default actions when the ignition is OFF long enough in order to power down the TCM.

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.

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.

3. Record the DTC Failure Records.
4. Clear the DTC.
5. Start the engine.
6. Move the A/T Shift Lever to the Manual position.
7. Select IMS on the scan tool.

Does the scan tool IMS parameter display Drive 5?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

1. Select IMS A/B/C/P on the scan tool.
2. Place the gear select lever in the Manual position.

Does the scan tool IMS A/B/C/P display indicate the specified value for each range?

HI/HI/HI/HI

Go to Step 14

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 Manual Shift Shaft Position Switch Replacement .

Did the linkage require adjustment?

--

Go to Step 19

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Disconnect the AT inline 20-way connector. Additional DTCs may set.
3. Turn ON the ignition with the engine OFF.
4. Select IMS A/B/C/P on the scan tool.

Does the scan tool IMS A/B/C/P display all HI?

--

Go to Step 6

Go to Step 10

6 |

1. Turn OFF the ignition.
2. Install the J 45681 jumper harness on the TCM side of the AT inline 20-way connector.
3. Turn ON the ignition with the engine OFF.
4. Using the DMM and the J 35616 GM terminal test kit, measure the voltage at the Transmission Range (TR) signal A circuit of the J 45681 . Refer to Automatic Transmission Inline 20-Way Connector End View .
5. Measure the voltage at the TR signal B of the J 45681 .
6. Measure the voltage at the TR signal C of the J 45681 .
7. Measure the voltage at the TR signal P of the J 45681 .

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 J 45681 to ground while monitoring the scan tool IMS A/B/C/P display. Refer to Automatic Transmission Inline 20-Way Connector End View . 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 J 45681 to ground while monitoring the scan tool IMS A/B/C/P display. Refer to Automatic Transmission Inline 20-Way Connector End View . 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 J 45681 to ground while monitoring the scan tool IMS A/B/C/P display. Refer to Automatic Transmission Inline 20-Way Connector End View . When the TR signal C circuit is grounded, do any other circuits indicate LOW? | -- | Go to Step 12 | Go to Step 13
10 | Test the TR signal circuits of the transmission manual shift shaft switch assembly that did not indicate HI for a short to ground between the TCM connector and the AT inline 20-way connector. Refer to Testing for Short to Ground and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

11 | Test the TR signal circuits of the transmission manual shift shaft switch assembly that did not indicate ignition voltage for an open between the TCM connector and the AT inline 20-way connector. Refer to Testing for Continuity and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 19

Go to Step 18

12 | Test the affected signal circuits of the transmission manual shift shaft switch assembly for a shorted together condition between the TCM connector and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18
13 | Test the TR signal circuits of the transmission manual shift shaft switch assembly for an open or shorted condition between the AT inline 20-way connector and the switch. Refer to Testing for Continuity . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 17
14 | Test the ground circuit of the transmission manual shift shaft switch assembly for an open between the AT inline 20-way connector and the chassis. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 15
15 | Test the ground circuit of the transmission manual shift shaft switch assembly for an open between the AT inline 20-way connector and the switch. Refer to Testing for Continuity . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 17
16 | Replace the automatic transmission wiring harness assembly. Refer to Transmission Internal Electrical Harness Replacement . Did you complete the replacement? | -- | Go to Step 19 | --
17 | Replace the transmission manual shift shaft switch assembly. Refer to Manual Shift Shaft Position Switch Replacement . Did you complete the operation? | -- | Go to Step 19 | --
18 | Replace the TCM. Refer to Control Module References for replacement, setup and programming. Did you complete the operation? | -- | Go to Step 19 | --
19 | Perform the following procedures in order to verify the repair:

1. Select the 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 P1876.

Has the test run and passed?

--

Go to Step 20

Go to Step 2

20 | 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? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK