Circuit Description
The 1-2 shift solenoid valve is located in the control valve body of the transmission. The transmission control module (TCM) selects the required gear by turning the appropriate solenoid ON or OFF, enabling the transmission to shift. Refer to Shift Solenoid Valve State and Gear Ratio .
The TCM provides voltage to the solenoid through High Side Driver 2 (HSD2). The TCM uses a second driver to control the solenoid ground circuit. The controlled ground driver reports feedback voltage to the TCM. When the TCM commands the 1-2 shift solenoid valve ON, the voltage of the control circuit should be approximately 0 volts. When the TCM commands the 1-2 shift solenoid valve OFF, the voltage of the control circuit should be approximately system voltage.
When the TCM detects a continuous short to voltage in the 1-2 shift solenoid valve circuit, then DTC P0974 sets. DTC P0974 is a type B DTC.
Conditions for Running the DTC
| • | The engine run time is greater than 5 seconds. |
| • | HSD2 is commanded ON. |
Conditions for Setting the DTC
DTC P0974 sets when the TCM detects a short to voltage in the 1-2 shift solenoid valve circuit for 4.3 seconds.
Action Taken When the DTC Sets
| • | The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL) during the second consecutive drive trip in which the Conditions for Setting the DTC are met. |
| • | The TCM commands maximum line pressure. |
| • | The TCM inhibits 3-2 downshifts if the vehicle speed is greater than 8 km/h (5 mph). |
| • | 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 P0974 in TCM history. |
Diagnostic Aids
DTC P 1843 may set when a communication fault exists between the ECM and TCM. Inspect for DTC C0100. If this DTC is present, diagnose it first.
Conditions for Clearing the MIL/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 MIL/DTC. |
| • | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring. |
| • | The TCM cancels the 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.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Automatic Transmission? | -- | Go to Step 2 | |||||
Important:
Does the solenoid click? | -- | Go to Step 8 | Go to Step 3 | |||||
3 |
Does the test lamp illuminate? | -- | Go to Step 4 | Go to Step 6 | ||||
4 |
Refer to Component Resistance . Is the resistance within the specified range? | 15.0-20.3ohms | Go to Step 5 | Go to Step 7 | ||||
5 |
Did you find a condition? | -- | Go to Step 9 | Go to Step 8 | ||||
6 |
Did you find a condition? | -- | Go to Step 9 | Go to Step 8 | ||||
7 |
Did you find a condition? | -- | Go to Step 10 | Go to Step 11 | ||||
8 | Replace the TCM. Refer to Transmission Control Module Replacement . Is the action complete? | -- | Go to Step 12 | -- | ||||
9 | Perform the necessary wiring repairs. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 12 | -- | ||||
10 | Replace the AT internal transmission wiring harness. Refer to Transmission Internal Electrical Harness Replacement . Is the action complete? | -- | Go to Step 12 | -- | ||||
11 | Replace the 1-2 shift solenoid valve. Refer to 1-2 Shift Solenoid Valve Replacement . Is the action complete? | -- | Go to Step 12 | -- | ||||
12 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 13 | Go to Step 2 | ||||
13 | 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? | -- | System OK |
