For 1990-2009 cars

## DTC P1843 3.0L (L81)

Master Electrical Component List
Automatic Transmission Controls Schematics 3.0L
OBD II Symbol Description Notice

### Circuit Description

The 1-2 shift solenoid (SS) valve controls transmission fluid pressure acting on the 1-2 and 2-3 shift valves to position the valves for the appropriate gear. The 1-2 SS valve is a normally open exhaust valve located on the control valve body. The transmission control module (TCM) provides voltage to the pressure control solenoid, the shift solenoids, and the TCC PWM solenoid through two separate solid-state devices called High Side Drivers, called HSD1 and HSD2. HSD1 provides electrical power to the pressure control solenoid. HSD2 provides electrical power to the shift solenoids, and the TCC PWM solenoid. The TCM then commands the solenoid ON or OFF by also providing a ground path. When the 1-2 SS valve is commanded ON, the TCM senses low voltage. When the 1-2 SS valve is commanded OFF, the TCM senses high voltage.

If the TCM detects a continuous open or short to voltage in the 1-2 SS valve circuit, then DTC P1843 sets. DTC P1843 is a type A DTC.

### Conditions for Running the DTC

• | The engine run time is greater than 5 seconds.

• | The TCM commands the 1-2 SS valve ON.

### Conditions for Setting the DTC

The 1-2 SS valve feedback circuit indicates a continuous short to voltage for 4.3 seconds.

### Action Taken When the DTC Sets

• | The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL).

• | The TCM commands maximum line pressure.

• | The TCM inhibits 3-2 downshifts above 52 km/h (32 mph).

• | The TCM inhibits TCC engagement.

• | The TCM freezes transmission adaptive functions.

• | The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records.

• | The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records.

• | The TCM stores DTC P1843 in TCM history.

### Conditions for Clearing the MIL/DTC

• | The ECM turns OFF the MIL after the third 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 DTC default actions when the ignition switch is OFF long enough in order to power down the TCM.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step tests the TCM and the wiring to the transmission.

2. This step verifies that the circuit has the correct resistance.

#### DTC P1843

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 - 3.0L (L81)
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 Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from both the ECM and the TCM.

3. Record the DTC Freeze Frame and Failure Records.
4. Clear the DTC.
5. Start the engine.

Did DTC P1843 reset?

--

Go to Step 3

Go to Intermittent Conditions in Engine Controls - 3.0L (L81)

3 |

1. Turn OFF the ignition.
2. Disconnect the AT inline 20-way connector. Additional DTCs may set.
3. Install the J 44152 jumper harness (20 pins) on the engine side of the AT inline 20-way connector.
4. Using the J-35616 connector test adapter kit, connect a test lamp between terminal A of the J 44152 and ground.

Refer to Automatic Transmission Inline 20-Way Connector End View .

5. Turn ON the ignition, with the engine OFF.

Is the test lamp ON?

--

Go to Step 4

Go to Step 5

4 | Test the control circuit (CKT 1222) of the 1-2 SS valve for a short to voltage between the TCM connector C2 and the AT inline 20-way connector. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
5 |

1. Turn OFF the ignition.
2. Disconnect the J 44152 from the engine side of the AT inline 20-way connector.
3. Install the J 44152 on the transmission side of the AT inline 20-way connector.
4. Using the DMM and the J-35616 connector test adapter kit, measure the resistance between terminals E and A of the J 44152 .

Refer to Automatic Transmission Inline 20-Way Connector End View .

Is the resistance within the specified range?

19-31 ohms

Go to Step 7

Go to Step 6

6 |

1. Leave the DMM test leads connected.
2. Disconnect the 1-2 SS valve from the automatic transmission wiring harness.

Is the resistance less than the specified value?

100 ohms

Go to Step 8

Go to Step 9

7 | Measure the resistance between terminal A and all other terminals, except terminals B, T 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, T and E, less than the specified value? | 100 ohms | Go to Step 8 | Go to Intermittent Conditions in Engine Controls - 3.0L (L81)
8 | Replace the automatic transmission wiring harness. Refer to Wiring Harness Removal . Did you complete the replacement? | -- | Go to Step 11 | --
9 | Replace the 1-2 SS valve. Refer to Control Valve Body Disassemble in Unit Repair. Did you complete the replacement? | -- | Go to Step 11 | --
10 | Replace the TCM. Refer to Transmission Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
11 | Perform the following procedure in order to verify the repair:

1. Select DTC.
2. Select Clear Info.
3. Start the engine.
4. Select Specific DTC.
5. Enter DTC P1843.

Has the test run and passed?

--

Go to Step 12

Go to Step 2

12 | 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 - 3.0L (L81) | System OK