Circuit Description
The 1-2 shift solenoid (SS) valve controls transmission fluid pressure acting on the 1-2 and 3-4 shift valves to position the valves for the appropriate gear. The 1-2 SS valve is a normally open exhaust valve located on the lower control valve body. Ignition voltage is supplied to the solenoid. The output driver module (ODM), within the PCM, commands the solenoid ON or OFF by providing a ground path. When the 1-2 SS valve is commanded ON, the PCM senses low voltage. When the 1-2 SS valve is commanded OFF, the PCM senses high voltage.
If the PCM detects a continuous open or short to ground in the 1-2 SS valve circuit, then DTC P1842 sets. DTC P1842 is a type B DTC.
Conditions for Running the DTC
| • | The system voltage is 8-18 volts. |
| • | The engine run time is greater than 5 seconds. |
Conditions for Setting the DTC
The 1-2 SS valve feedback circuit indicates a continuous open or short to ground for 4.3 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. |
| • | The PCM commands maximum line pressure. |
| • | The PCM inhibits 3-2 downshifts above 50 km/h (31 mph). |
| • | The PCM freezes transmission adapt functions. |
| • | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records. |
| • | The PCM stores DTC P1842 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes. |
| • | A scan tool can clear the MIL/DTC. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring. |
| • | The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the electrical operation of the solenoid.
-
This step tests the PCM and the wiring to the transmission.
-
This step verifies that the circuit has the correct resistance.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain Diagnostic System Check? | -- | ||||||
2 |
Important: Before clearing the DTC, use the Scan Tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM. Is DTC P1845 or P1860 also set? | -- | ||||||
3 |
Refer to Wiring Repairs in Wiring Systems. Did you find the condition? | -- | ||||||
4 |
Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics in Wiring Systems for complete circuit distribution. Test the ignition 1 voltage circuit (CKT 739) of the 1-2 SS valve for a short to ground between the underhood fuse block and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||
5 |
Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics in Wiring Systems for complete circuit distribution. Test the ignition 1 voltage circuit (CKT 839) of the 1-2 SS valve for a short to ground between the AT inline 20-way connector and the 1-2 SS valve. Refer to Circuit Testing in Wiring Systems. Did you find the condition? | -- | -- | |||||
6 | Test the ignition 1 voltage circuit (CKT 739) of the 1-2 SS valve for an open between the underhood fuse block and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||
7 | Test the ignition 1 voltage circuit (CKT 839) of the 1-2 SS valve for an open between the AT inline 20-way connector and the 1-2 SS valve. Refer to Circuit Testing in Wiring Systems. Did you find the condition? | -- | -- | |||||
Does the solenoid click when commanded ON and OFF? | -- | Go to Intermittent Conditions | ||||||
Refer to Automatic Transmission Inline Harness Connector End View . Is the test lamp ON when you command the solenoid ON, and OFF when you command the solenoid OFF? | -- | |||||||
10 | Is the test lamp always ON? | -- | ||||||
11 |
Is the test lamp ON? | -- | ||||||
12 | Test the control circuit (CKT 1222) of the 1-2 SS valve for a short to ground between the PCM connector C2 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |||||
13 | Test the control circuit (CKT 1222) of the 1-2 SS valve for an open between the PCM connector C2 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||
14 |
Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance within the specified range? | 20-40 ohms | ||||||
15 | Is the resistance greater than the specified value? | 40 ohms | ||||||
16 |
Refer to Circuit Testing in Wiring Systems. Did you find a condition? | -- | ||||||
Measure the resistance from terminal A of the J 44152 to ground. Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance less than the specified value? | 100 ohms | |||||||
18 | Test the control circuit (CKT 1222) of the 1-2 SS valve for a short to ground between the AT inline 20-way connector and the 1-2 SS valve. Refer to Circuit Testing in Wiring Systems. Did you find the condition? | -- | -- | |||||
19 |
Important: The automatic transmission wiring harness consists of two separate harnesses, the Automatic Transmission Wiring Harness Assembly (GM P/N 1532 0475) and the Automatic Transmission Wiring Extension Harness Assembly (GM P/N 1532 0478). In order to avoid the unnecessary replacement of parts, determine which harness contains the fault and replace only that harness. Replace the automatic transmission wiring harness. Refer to Transmission Overhaul in Transmission Unit Repair Manual. Did you complete the replacement? | -- | -- | |||||
20 | Replace the 1-2 SS valve. Refer to Solenoid A Replacement. Did you complete the replacement? | -- | -- | |||||
21 | Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Did you complete the replacement? | -- | -- | |||||
22 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
