The automatic transmission manual shift shaft position assembly, also known as an internal mode switch (IMS), is a sliding contact switch that mounts to the lower control valve body. The switch has a sliding rail that connects to the transmissions’ manual valve. The slide rail follows the position of the manual valve to provide manual valve location to the transmission control module (TCM) and engine control module (ECM). Internal to the switch are metal contact finger that attach to a slide rail. The fingers make contact with segmented stainless steel strips that run the length of the switch. Contact between the fingers and the stainless steel strips will cause the TCM signal voltage to be Low, 0 volts, when there is no contact between a finger and a strip, the TCM signal voltage will remain High, 12 volts. As a result of the different High and Low signal combinations, the TCM and ECM can decode the transmission manual valve position. For diagnostic purposes, the High and Low signals can be displayed on the scan tool. There are four signal circuits used to identify the manual valve position and are identified as parameter A, B, C and P, parity. The switch also has two additional circuits which are D, a common ground circuit and S, a Park/Neutral start circuit for the ECM. The P/N signal circuit goes from the switch directly to the ECM, using the transmission 16-way connector as a passing through only. The P/N circuit does not go into the TCM, only the ECM, where it can be viewed on the scan tool through the ECM. The TCM and ECM use the decoded information for engine controls, starter enable, as well as determining the transmission shift patterns and driver shift requests (DSR) usage.

P1825

P1915

P1825

Any one of the following Fail Cases occur:

Fail Case 1

The TFP Switch 3 or TFP Switch 4 is pressurized with the commanded gear 1st - engine braking and the IMS indicates a 01 (Invalid) transitional state for 8 seconds or more.

Fail Case 2

The TFP Switch 3 or TFP Switch 4 is pressurized and the IMS indicates a TRAN 13 Park/Reverse transitional state for 8 seconds or more.

Fail Case 3

The TFP Switch 3 or TFP Switch 4 is pressurized and the IMS indicates a Invalid transitional state for 1.25 seconds or more 6 times during the same ignition cycle.

Fail Case 4

The IMS indicates an invalid range or the IMS state and the ECM Park/Neutral signal do not match for 6.25 seconds or greater.

Fail Case 5

The TFP Switch 3 or TFP Switch 4 is pressurized, the vehicle speed is 16 km/h (10 mph) or greater, and the IMS indicates a Drive 4/Drive 3 transitional state for 3 seconds or greater.

P1915

The manual shift shaft IMS switch assembly does not indicate Park or Neutral during the following sequence:

DTCs P1825 and P1915 are Type A DTCs.

Disconnecting the 16-way connector from the transmission will disable TCM and ECM communications.

The IMS is part of a 6 wire harness, which connects electrically to the control solenoid (w/body and TCM) valve assembly. Inspect the IMS, harness, connector, and control solenoid (w/body and TCM) valve assembly electrical pins for metallic debris. Use a terminal test kit for any test that requires probing the control solenoid (w/body and TCM) valve assembly harness connector or a component harness connector.

Use the Internal Mode Switch Logic table to compare scan tool reading with the transmission fluid pressure (TFP) switch. TFP switch states should correspond to the correct gear positions. Be sure to look for switch positions which are transitional, displays invalid or open. These are not normal IMS positions when shifter detents are properly engaged.

Use the scan tool IMS parameters to compare them to the ECM P/N parameter. When the transmission is in park or neutral, the ECM P/N switch parameter will read park/neutral. When the transmission is in a drive range, the P/N will read In Gear. Be alert for scan tool data parameters which frequently toggle or vary while testing. Switch positions which are transitional, display invalid or are open are not normal IMS positions when shifter detents are engaged.

Due to the properties of the stainless steel contact strips inside the switch, it is difficult to obtain meaningful resistance readings. For this reason, measuring the switch resistance may not help to conclude a faulty switch. However, the absence of all resistance where there should be would indicate a circuit failure.

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

Description and Operation

Electronic Component Description

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Test for the correct operation of the IMS. Refer to Transmission Internal Mode Switch Logic .

1. Disconnect the IMS connector at the control solenoid (w/body and TCM) valve assembly. Ignition On. The scan tool IMS A/B/C/P parameter should display HI for all four signal circuits.

⇒	If a signal circuit displays LOW, the control solenoid (w/body and TCM) valve assembly is faulty.

2. Connect a 3-amp fused jumper wire between each transmission range signal circuit at the control solenoid (w/body and TCM) valve assembly and ground ensuring the signal circuit displays LOW when connected to ground.

⇒	If a signal circuit remains HI when connected to ground, the control solenoid (w/body and TCM) valve assembly is faulty.

⇒	If the above two tests indicate correct TCM functions, the IMS is faulty.

If the IMS switch is replaced inspect the valve body detent spring to be sure it is centered over the detent lever. This will prevent the detent spring from hitting the IMS switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Important: Perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection for the following components before replacing the components.