GM Service Manual Online
For 1990-2009 cars only

Object Number: 1402935  Size: LF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The transmission manual shift shaft switch assembly is a sliding contact switch attached to the control valve body within the transmission. The four inputs to the transmission control module (TCM) from the switch indicate which position is selected by the transmission selector lever. This information is used for engine controls as well as determining the transmission shift patterns. The input voltage level at the TCM is high when the switch is open and low when the switch is closed to ground. The state of each input is displayed on the scan tool as IMS. The four IMS input parameters represented are Signal A, Signal B, Signal C and Signal P (Parity).

If the TCM detects switch Signal C is high while the vehicle is being driven in a forward gear, then DTC P1826 sets. DTC P1826 is a type B DTC.

Conditions for Running the DTC

    • No OSS DTCs P0722 or P0723.
    • No engine torque signal DTC P2637.
    • Vehicle speed is greater than 8 km/h (5 mph).
    • Engine torque is greater than 20 N·m (15 lb ft).
    • DTC P1826 has not passed during the current ignition cycle.
    • The gear ratio is within one of the following ranges:
       - 3.33:1 to 3.50:1 for first gear
       - 2.16:1 to 2.27:1 for second gear
       - 1.56:1 to 1.64:1 for third gear
       - 0.98:1 to 1.03:1 for fourth gear
       - 0.73:1 to 0.77:1 for fifth gear

Conditions for Setting the DTC

The TCM detects Signal C is high, while the gear ratio indicates first, second, third, fourth, or fifth gear for 3 seconds.

Action Taken When the DTC Sets

    • The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
    • The TCM commands maximum line pressure.
    • The TCM freezes transmission adaptive functions.
    • The TCM assumes a D5 shift pattern.
    • At the time of the first failure, the TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record.
    • At the time of the second failure, the ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as a Freeze Frame.
    • The TCM stores DTC P1826 in TCM history.

Conditions for Clearing the DTC

    • The ECM turns OFF the MIL after the sixth consecutive drive trip in which the TCM does not send a MIL illumination request.
    • 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.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step tests the integrity of the engine harness and TCM by checking for the Signal C state change from HI to LOW. A LOW signal indicates the fault is in the internal transmission harness or the switch. A HI signal indicates the fault is in the engine harness or the TCM.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

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 ECM Freeze Frame and the TCM Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the ECM and the TCM.
       • Using the Clear Info function erases stored DTCs in both the ECM and TCM.

  4. Record the DTC Freeze Frame and Failure Records.
  5. Clear the DTC.
  6. Select Transmission Data on the scan tool.
  7. Select IMS range on the scan tool.
  8. Place the range selector in D5.

Does the scan tool IMS range indicate Drive 5?

--

Go to Intermittent Conditions in Engine Controls - 4.6L

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the AT inline 20-way connector. Additional DTCs may set.
  3. Install the J 45681 jumper harness on the TCM side of the AT inline 20-way connector.
  4. Using the J 35616 GM terminal test kit, connect a fused jumper wire from the TR signal C circuit of the J 45681 to ground.
  5. Refer to Automatic Transmission Inline 20-Way Connector End View .

  6. Turn ON the ignition, with the engine OFF.
  7. Select IMS A/B/C/P on the scan tool.

Does IMS Signal C indicate LOW?

--

Go to Step 5

Go to Step 4

4

Test the TR signal C circuit of the transmission manual shift shaft switch assembly for an open between the TCM connector and the AT inline 20-way connector.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 9

Go to Step 8

5

Test the TR signal C 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 in Wiring Systems.

Did you find the condition?

--

Go to Step 6

Go to Step 7

6

Replace the automatic transmission wiring harness. Refer to Transmission Internal Electrical Harness Replacement .

Is the action complete?

--

Go to Step 9

--

7

Replace the transmission manual shift shaft switch assembly.

Refer to Parking System Components Removal in Transmission Unit Repair Manual.

Is the action complete?

--

Go to Step 9

--

8

Replace the TCM. Refer to Transmission Control Module Replacement .

Is the action complete?

--

Go to Step 9

--

9

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Start and idle the engine in PARK.
  4. Observe IMS A/B/C/P on the scan tool.
  5. Move the range selector to D2, D3, D4 and D5 positions. Ensure that IMS Signal C indicates LOW for each range.
  6. Operate the vehicle to greater than 8 km/h (5 mph).
  7. Select Specific DTC.
  8. Enter DTC P1826.

Has the test run and passed?

--

Go to Step 10

Go to Step 2

10

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 in Vehicle DTC Information

System OK