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 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 commands the TCC ON in 3rd and 4th gear when in Hot Mode, if the brake switch status remains closed and no downshifts are commanded. |
| • | The PCM freezes transmission adaptive 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 Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls in Engine Controls | ||||
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? | -- | Go to Step 3 | Go to Step 8 | ||||
3 |
Refer to Circuit Protection - Fuses in Wiring Systems. Did you find the condition? | -- | Go to Step 4 | Go to Step 6 | ||||
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 Testing for Short to Ground and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 5 | ||||
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 Testing for Short to Ground in Wiring Systems. Did you find the condition? | -- | Go to Step 20 | -- | ||||
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 Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 7 | ||||
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 Testing for Continuity in Wiring Systems. Did you find the condition? | -- | Go to Step 20 | -- | ||||
Does the solenoid click when commanded ON and OFF? | -- | Go to Intermittent Conditions in Engine Controls | Go to Step 9 | |||||
Refer to Automatic Transmission Inline 20-Way Connector End View . Is the test lamp ON when you command the solenoid ON, and OFF when you command the solenoid OFF? | -- | Go to Step 14 | Go to Step 10 | |||||
10 | Is the test lamp always ON? | -- | Go to Step 11 | Go to Step 13 | ||||
11 |
Is the test lamp ON? | -- | Go to Step 12 | Go to Step 22 | ||||
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 Testing for Short to Ground and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 23 | -- | ||||
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 Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 22 | ||||
Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance within the specified range? | 20-40 ohms | Go to Step 17 | Go to Step 15 | |||||
15 | Is the resistance greater than the specified value? | 40 ohms | Go to Step 16 | Go to Step 17 | ||||
16 |
Refer to Testing for Continuity in Wiring Systems. Did you find a condition? | -- | Go to Step 20 | Go to Step 21 | ||||
17 | Measure the resistance from terminal A of the J 44152 to ground. Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance less than the specified value? | 100 ohms | Go to Step 18 | Go to Step 19 | ||||
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 Testing for Short to Ground in Wiring Systems. Did you find the condition? | -- | Go to Step 20 | -- | ||||
19 | Measure the resistance between terminal A and all other terminals, except terminals B and E, of the J 44152 . Refer to Automatic Transmission Inline 20-Way Connector End View . Is the resistance between terminal A and any other terminal, except terminals B and E, less than the specified value? | 100 ohms | Go to Step 20 | Go to Step 21 | ||||
20 |
Important: The automatic transmission wiring harness consists of two separate harnesses, the Automatic Transmission Wiring Harness Assembly, GM P/N 15320475, and the Automatic Transmission Wiring Extension Harness Assembly, GM P/N 15320478. 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 Input Speed Sensor and Wiring Harness Removal in the 4T80-E section of the Transmission Unit Repair Manual. Did you complete the replacement? | -- | Go to Step 23 | -- | ||||
21 | Replace the 1-2 SS valve. Refer to Control Valve Lower Body Disassemble in the 4T80-E section of the Transmission Unit Repair Manual. Did you complete the replacement? | -- | Go to Step 23 | -- | ||||
22 | Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Did you complete the replacement? | -- | Go to Step 23 | -- | ||||
23 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 24 | Go to Step 2 | ||||
24 | 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 in Engine Controls | System OK |
