For 1990-2009 cars

### 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.

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.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1826 Internal Mode Switch C Circuit High Voltage

### Conditions for Running the DTC

• | Ignition voltage is between 8-18 volts.

• | No OSS DTC P0722 or P0723.

• | Engine torque default values are not being used.

• | Vehicle speed is greater than 2 km/h (1.25 mph).

• | The gear ratio is within one of the following ranges:

- | 3.32:1 to 3.52:1 for first gear

- | 2.16:2 to 2.28:1 for second gear

- | 1.55:1 to 1.65:1 for third gear

- | 0.97:1 to 1.03:1 for fourth gear

- | 0.73:1 to 0.77:1 for the fifth gear

• | DTC P1826 has not passed during the current ignition cycle.

• | The TCM detects a short to power in the switch signal C circuit for 5 seconds.

### Conditions for Setting the DTC

The TCM detects an open circuit flag in the switch signal C circuit for 5 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 assumes a D5 shift pattern.

• | The TCM freezes transmission adaptive functions.

• | 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? | -- | 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 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.

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

Does the scan tool IMS range indicate Drive?

--

Go to Testing for Intermittent Conditions and Poor Connections

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.

Refer to Component Connector End Views.

5. Turn ON the ignition with the engine OFF.
6. 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. 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. 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. Did you complete the operation? | -- | Go to Step 9 | --
7 | Replace the transmission manual shift shaft switch assembly. Refer to Manual Shift Shaft Position Switch Replacement. Did you complete the operation? | -- | Go to Step 9 | --
8 | Replace the TCM. Refer to Control Module References for replacement, setup and programming. Did you complete the operation? | -- | Go to Step 9 | --
9 | Perform the following procedures in order to verify the repair:

1. Select the 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 D positions. Ensure that IMS Signal C indicates LOW for each range.
6. Operate the vehicle to greater than 2 km/h (1.25 mph) in all gears.
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 | System OK