For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P1825: Internal Mode Switch - Invalid Range
DTC P1915: Internal Mode Switch Start/Wrong Range

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Transmission Range Signal A | P1825 | P1915 | P1915 | P1825, P1915
Transmission Range Signal B | P1915 | P1825 | P1825 | P1825, P1915
Transmission Range Signal C | P1915 | P1825 | P1825 | P1825, P1915
Transmission Range Signal P | P1825 | P1915 | P1915 | P1825, P1915
Ground | -- | P1825 | P1825 | P1825, P1915

### Typical Scan Tool Data

#### IMS A/B/C/P

Circuit | Normal Range | Short to Ground | Open | Short to Voltage
--- | --- | --- | --- | ---
Operating Conditions: Ignition ON, range selector in Park
Transmission Range Switch Signal A | LOW | LOW | HI | HI
Transmission Range Switch Signal B | HI | LOW | HI | HI
Transmission Range Switch Signal C | HI | LOW | HI | HI
Transmission Range Switch Signal P | LOW | LOW | HI | HI
HI = 12 volts LOW = 0 volts

### Circuit/System Description

The internal mode switch (IMS) assembly is a sliding contact switch attached to the control valve body within the transmission. The 4 inputs to the transmission control module (TCM) from the switch indicate which position is selected by the transmission manual shaft. 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 scan tool as IMS. The IMS input parameters represented are transmission range signal A, Signal B, signal C, and signal P.

### Conditions for Running the DTC

#### P1825

Start the ignition voltage, run the engine.

• | For conditions 1:

| The state of pressure switch on PC Sol.5 or PC Sol.4 is pressure applying, commanded gear equals first lock.

• | For conditions 2:

| The state of pressure switch on PC Sol.5 or PC Sol.4 is pressure applying.

• | For conditions 3:

| The state of pressure switch on PC Sol.5 or PC Sol.4 is pressure applying.

• | For conditions 4:

| The serial data signal of ECM is in PARK/ NUETRAL position or not in PARK/NUETRAL position.

• | For conditions 5:

- | Vehicle Speed Sensor (VSS) is greater than 16 km/h (10 mph).

- | The state of pressure switch on PC Sol.5 or PC Sol.4 is pressure applying.

#### P1915

• | The ignition voltage is between 6 and 18 volts.

• | No DTC P0722 or P0723.

• | The transmission output shaft speed is less than 90 RPM.

### Conditions for Setting the DTC

#### P1825

Fail Case 1:

• | The IMS is in a transitional state of 6th/4th gear, signal circuit P is high for 8 seconds

• | Occurs at least once.

Fail Case 2:

• | The IMS signal is in a transitional state of 3rd/ 2nd gear, signal circuit C is low for 8 seconds.

• | Occurs at least once.

Fail Case 3:

• | The IMS signal is in a transitional state of Neutral/6th gear, signal circuit A is low for 1.25 seconds.

• | Occurs at least 6 times.

Fail Case 4:

Park/Neutral Switch equals P/N and the IMS state is not Park or Neutral, or the Park/Neutral switch is not Park or Neutral and the IMS state equals Park or Neutral for 6.25 seconds.

Fail Case 5:

• | The IMS signal is in a transitional state of Reverse/Neutral gear, signal circuit B is low for 3 seconds.

• | Occurs at least once.

#### P1915

The transmission gear in not in park or neutral position.

The manual shift shaft switch assembly indicates a transitional state during the following sequence:

• | The engine speed is less than 50 RPM for more than 0.25 seconds.

• | The engine speed is 50-480 RPM for more than 0.07 seconds.

• | The engine speed is greater than 525 RPM for more than 3.25 seconds.

• | The transmission input shaft speed is greater than 200 RPM.

### Action Taken When the DTC Sets

• | DTCs P1825 and P1915 are Type A DTCs.

• | The TCM commands maximum line pressure.

• | The TCM turns OFF all solenoids.

• | The TCM freezes transmission adaptive functions.

• | The TCM defaults the transmission to third gear if the current gear is 1st, 2nd, or 3rd; or fifth gear if the current gear is 4th, 5th, or 6th gear.

### Conditions for Clearing the DTC

DTCs P1825 and P1915 are Type A DTCs.

### Diagnostic Aids

The IMS is part of a wire harness, which connects electrically to the control solenoid (w/body and TCM) valve assembly and is serviced separately from the control solenoid (w/body and TCM) valve assembly. Inspect the IMS, harness, connector, and control solenoid (w/body and TCM) valve assembly pins for metallic debris. Use the J 35616 GM-approved 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.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### DTC Type Reference

• | Diagnostic Trouble Code (DTC) Type Definitions

• | Diagnostic Trouble Code (DTC) List/Type

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Output Controls

• | Scan Tool Data List

• | Scan Tool Data Definitions

#### Special Tools

J 35616 GM-Approved Terminal Test Kit

### Circuit/System Verification

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

⇒ | If the IMS operation matches the IMS logic table, the system is functioning normally.

### Circuit/System Testing

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 that 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.

### Component Testing

#### Internal Mode Switch Logic Table

Gear Selector Position | A | B | C | P
--- | --- | --- | --- | ---
Park | LOW | HI | HI | LOW
Park/Reverse | LOW | LOW | HI | LOW
Reverse | LOW | LOW | HI | HI
Reverse/Neutral | HI | LOW | HI | HI
Neutral | HI | LOW | HI | LOW
Neutral/Drive 6 | HI | LOW | LOW | LOW
Drive 6 | HI | LOW | LOW | HI
Drive 4 | LOW | LOW | LOW | LOW
Drive 3 | LOW | HI | LOW | HI
Drive 2 | HI | HI | LOW | LOW
Invalid | HI | HI | HI | HI
LOW | HI | HI | HI
HI | HI | HI | LOW
HI = Ignition voltage LOW = 0 voltage

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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

• | Manual Shift Shaft Position Switch Replacement

• | Service Fast Learn Adapts

• | Control Module References for TCM replacement, setup, and programming