Circuit Description
The transmission manual shift shaft switch assembly is a sliding contact switch attached to the manual shift shaft inside the transmission case. There are four inputs to the Transmission Control Module (TCM) from the switch which indicate the position selected by the transmission selector lever. This information is used for engine controls as well as determining the transmission shift patterns. The input voltage 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 Tech 2 as IMS. The IMS input parameters represented are transmission range Signal A, Signal B, Signal C and Signal P (Parity).
If the TCM detects the IMS signal C circuit is high while the vehicle is being driven in a forward gear, then DTC P1826 sets which is a type 'B' DTC.
Conditions for Running the DTC
| • | Ignition voltage is between 8.0 and 18.0 volts. |
| • | DTC P1826 has not passed during the current ignition cycle. |
| • | The following DTCs are not set: |
| - | P2637 Engine Torque Signal Circuit - No Valid GMLAN Signal. |
| - | P0722 or P0723 - Transmission Output Speed Sensor. |
| • | The engine torque is more than 20 N·m. |
| • | Vehicle speed is more than 8 km/h. |
| • | The gear ratio is within one of the following ranges: |
| - | 3.33:1 to 3.50:1 for first gear OR |
| - | 2.16:1 to 2.27:1 for second gear OR |
| - | 1.56:1 to 1.64:1 for third gear OR |
| - | 0.98:1 to 1.03:1 for fourth gear OR |
| - | 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 Powertrain Interface Module (PIM) to illuminate the Check Powertrain Malfunction Indicator Lamp (MIL) in the instrument cluster during the second consecutive drive trip in which the 'Conditions for Setting the DTC' are met. |
| • | The TCM turns off the pressure control solenoid (causing maximum line pressure). |
| • | The TCM freezes the transmission adaptive learning function. |
| • | 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' have been 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' have been met. The ECM stores this information as a freeze frame. |
| • | The TCM stores DTC P1826 into TCM history during the second consecutive trip in which the 'Conditions for Setting the DTC' are met. |
Conditions for Clearing the MIL/DTC
| • | Tech 2 can clear the DTC. |
| • | The TCM clears the DTC from its memory (history DTC) if the vehicle completes 40 warm-up cycles without a non-emission related DTC occurring. |
| • | The TCM cancels the default actions when the ignition is off long enough to power down the TCM. |
| • | The PIM turns off the Check Powertrain MIL after the sixth consecutive drive trip in which the TCM does not send a Check Powertrain MIL illumination request. |
Test Description
The following number(s) refer to the step number(s) on the diagnostic table.
3. This step tests the integrity of the transmission wiring 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 transmission wiring harness or the TCM.
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics For information on testing wiring faults, refer to Wiring Systems. | ||||||||||||||
1 | Has the Diagnostic System Check - Automatic Transmission been completed? | -- | Go to Step 2 | |||||||||||
2 |
Does the Tech 2 IMS range display Drive 5? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | ||||||||||
3 |
Does the Tech 2 IMS Signal C display LOW? | -- | Go to Step 5 | Go to Step 4 | ||||||||||
4 | Using a digital ohmmeter, test the Transmission Range signal C circuit of the transmission shift shaft switch assembly for an open circuit condition between the transmission wiring harness TCM connector A112-T68, terminal X1-25 and the transmission wiring harness connector X121-X1, terminal X1-19. Did you find an open circuit condition? | -- | Repair open circuit condition. Go to Step 9 | Go to Step 8 | ||||||||||
5 |
Did you find an open circuit condition? | -- | Go to Step 6 | Go to Step 7 | ||||||||||
6 | Remove and replace transmission internal wiring harness. Refer to Transmission Internal Electrical Harness Replacement. Is replacement complete? | -- | Go to Step 9 | -- | ||||||||||
7 | Replace the transmission manual shift shaft switch assembly. Refer to Manual Shift Shaft Position Switch Replacement. Is replacement complete? | -- | Go to Step 9 | -- | ||||||||||
8 | Replace TCM. Refer to Transmission Control Module Replacement. Is the replacement complete? | -- | Go to Step 9 | -- | ||||||||||
9 |
Has the test run and passed? | -- | System OK | Go to Step 2 | ||||||||||
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | ||||||||||||||
