GM Service Manual Online
For 1990-2009 cars only

Object Number: 1492407  Size: LF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Control Module References

Circuit Description

The transmission internal mode switch (IMS) is a sliding contact switch attached to the lower control valve body, within the transmission. The manual valve link assembly then connects the IMS to the manual valve. The 4 inputs to the powertrain control module (PCM) from the IMS indicate which position is selected by the transmission selector lever. This information is used for engine controls as well as determining the transmission shift patterns. The input voltage level at the PCM is high, ignition voltage, when the IMS is open and low when the switch is closed to ground. The state of each input is available for display on the scan tool. The four input parameters represented are Signal A, Signal B, Signal C and Signal P, Parity.

Diagnostic Aids

Refer to Transmission Internal Mode Switch Logic .

Test Description

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

  1. This step tests the IMS for an open ground circuit.

  2. This step tests for correct reference voltage from the PCM.

Range Selector Displays Incorrect Range

Step

Action

Values

Yes

No

1

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. 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.

  4. Record the DTC Freeze Frame and Failure Records.
  5. Clear the DTC.
  6. Select IMS on the scan tool.
  7. Place the gear select lever in each transmission range: P, R, N, D4, D3, D2, and D1.

Does each range selected match the scan tool IMS display?

--

Go to Intermittent Conditions in Engine Controls

Go to Step 2

2

  1. Select IMS A/B/C/P on the scan tool.
  2. Place the gear select lever in each transmission range: P, R, N, D4, D3, D2, and D1.

Does the IMS A/B/C/P display match the specified value for each range selected?

HI/HI/HI/HI

Go to Step 12

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the AT inline 20-way connector. Additional DTCs may set.
  3. Turn ON the ignition, with the engine OFF.
  4. Select IMS A/B/C/P on the scan tool.

Does the scan tool IMS A/B/C/P parameter indicate HI for all range signal states?

--

Go to Step 4

Go to Step 8

4

  1. Turn OFF the ignition.
  2. Install the J 44152 Jumper Harness (20 pins) on the engine harness side of the AT inline 20-way connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Using the DMM and the J 35616 GM Terminal Test Kit, measure the voltage at terminal F of the J 44152 .
  5. Refer to Automatic Transmission Inline 20-Way Connector End View .

  6. Measure the voltage at terminal G of the J 44152 .
  7. Measure the voltage at terminal H of the J 44152 .
  8. Measure the voltage at terminal J of the J 44152 .

Does the voltage measure ignition voltage at all four terminals?

--

Go to Step 5

Go to Step 9

5

Connect a fused jumper wire from terminal F of the J 44152 , signal A circuit, to ground while monitoring the scan tool IMS A/B/C/P parameter.

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

When the signal A circuit is grounded, do any other signal circuits indicate LOW?

--

Go to Step 10

Go to Step 6

6

Connect a fused jumper wire from terminal G of the J 44152 , signal B circuit, to ground while monitoring the scan tool IMS A/B/C/P parameter.

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

When the signal B circuit is grounded, do any other signal circuits indicate LOW?

--

Go to Step 10

Go to Step 7

7

Connect a fused jumper wire from terminal H of the J 44152 , signal C circuit, to ground while monitoring the scan tool IMS A/B/C/P parameter.

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

When the signal C circuit is grounded, do any other signal circuits indicate LOW?

--

Go to Step 10

Go to Step 11

8

Test the signal circuits of the IMS that did not indicate HI for a short to ground between the PCM connector C3 and the AT inline 20-way connector.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 16

9

Test the signal circuits of the IMS that did not indicate ignition voltage for an open between the PCM connector C3 and the AT inline 20-way connector.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 16

10

Test the affected signal circuits of the IMS for a shorted together condition between the PCM connector C3 and the AT inline 20-way connector.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 16

11

Test the signal circuits of the IMS for an open or shorted condition between the AT inline 20-way connector and the IMS.

Refer to Circuit Testing in Wiring Systems.

Did you find a condition?

--

Go to Step 14

Go to Step 15

12

Test the ground circuit of the IMS for an open between the AT inline 20-way connector and ground.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 13

13

Test the ground circuit of the IMS for an open between the AT inline 20-way connector and the IMS.

Refer to Circuit Testing in Wiring Systems.

Did you find a condition?

--

Go to Step 14

Go to Step 15

14

Important: The automatic transmission wiring harness consists of 2 separate harnesses, the Automatic Transmission Wiring Harness Assembly and the Automatic Transmission Wiring Extension Harness Assembly. 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 17

--

15

Replace the transmission internal mode switch.

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 17

--

16

Replace the PCM.

Refer to Control Module References in Computer/Integrating Systems.

Did you complete the replacement?

--

Go to Step 17

--

17

  1. Turn ON the ignition, with the engine OFF.
  2. With the scan tool, observe the IMS display while selecting each transmission range: P, R, N, D4, D3, D2, and D1.

Does each selected transmission range match the scan tool IMS display?

--

System OK

Go to Step 2