GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Holden 🢒 2005 🢒 Statesman 🢒 DTC 🢒 DTC P1820

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 a short to ground on the IMS signal A circuit, then DTC P1820 sets, which is a type 'B' DTC.

Conditions for Running the DTC
    • Ignition voltage is between 8.0 and 18.0 volts.
    • Engine is running between 450 and 6,800 RPM for at least 5 seconds.
    • DTC P2637 Engine Torque Signal Circuit - No Valid GMLAN Signal is not set.
    • The engine torque is between 55 and 450 N·m.

Conditions for Setting the DTC
    • The transmission manual shift shaft switch assembly indicates Park for more than 1 second.
    • The switch indicates a transitional state for greater than 4 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.
    • 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 turns off the pressure control solenoid (causing maximum line pressure).
    • The TCM freezes the transmission adaptive learning function.
    • The TCM defaults to a D5 shift pattern.
    • The TCM stores DTC P1820 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 determines if the fault is internal or external to the transmission.

4. This step determines if the transmission wiring harness circuit or the TCM is at fault.

5. This step determines if the automatic transmission wiring harness or the transmission manual shift shaft switch assembly is at fault.

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

Go to Diagnostic System Check - Automatic Transmission

2
  1. Connect the Tech 2 to the DLC.
  2. Ignition ON, engine OFF.
  3. Clear the DTCs.
  4. Select 'Transmission Data' on the Tech 2.
  5. Select IMS range data parameter on TECH2.
  6. Place the gear selector lever into Park, then move to Neutral.

Does each range selected match the Tech 2 IMS range display?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3
  1. Ignition OFF.
  2. Disconnect transmission wiring harness connector X121-X1 from the transmission 20-way connector.
  3. Ignition ON, engine OFF.
  4. Select IMS A / B / C / P on Tech 2.

Does the Tech 2 IMS Signal 'A' display LOW?

--

Go to Step 4

Go to Step 5

4

Using a digital ohmmeter, test the Transmission Range signal A circuit 771 of the transmission shift shaft switch assembly for a short to ground condition between transmission wiring harness TCM connector A112-T68, terminal X1-36 and transmission wiring harness connector X121-X1, terminal X1-16.

Did you find a short to ground condition?

--

Repair short to ground condition in relevant circuit.

Go to Step 9

Go to Step 8

5
  1. Ignition OFF.
  2. Remove the transmission fluid pan. Refer to Transmission Control Module Replacement.
  3. Inspect transmission internal wiring harness for any sign of damage.
  4. Disconnect transmission internal wiring harness connector from the transmission shift shaft switch assembly.
  5. Ignition ON, engine OFF.
  6. Select IMS A / B / C / P on the Tech 2.

Does the Tech 2 IMS Signal A display LOW?

--

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

Perform the following operation to verify the repair:

  1. Select DTC on Tech 2.
  2. Select 'Clear info'.
  3. Operate the vehicle under the following conditions:
    4. • Drive the vehicle in D4.
    • The engine torque is between 55 and 450 N.m. IMS Signal A must be HI for 0.025 second.

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.