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 Does Not Indicate Park/Neutral (P/N) During Start

### Diagnostic Fault Information

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

• | The engine speed is greater than 500 RPM for 5 seconds.

• | The ignition voltage is between 9.0 volts and 19.0 volts.

• | Either the C1234 or CB26 pressure switch is pressurized.

#### P1915

• | No OSS DTCs P0722 or P0723.

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

• | The ignition voltage is between 6.0 volts and 18.0 volts.

### Conditions for Setting the DTC

#### 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 locked and the IMS indicates a Drive 6/Drive 4 transitional state for at least 0.225 seconds 15 or more times.

#### Fail Case 2

The TFP Switch 3 or TFP Switch 4 is pressurized and the IMS indicates a Drive 3/Drive 2 transitional state for at lease 0.225 seconds 15 or more times.

#### Fail Case 3

The TFP Switch 3 or TFP Switch 4 is pressurized and the IMS indicates a Neutral/Drive 6 transitional state for at least 0.225 seconds 15 or more times.

#### Fail Case 4

The IMS indicates an invalid range or the IMS state and the ECM Park/Neutral Signal do not match for 2.0 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 Reverse/Neutral transitional state for at least 0.225 seconds 15 or more times.

#### P1915

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

• | The engine speed is less than 50 RPM for more than 0.10 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 1.25 seconds.

• | The transmission input shaft speed is 100 RPM or greater.

### 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 3rd gear if the current gear is 1st, 2nd, or 3rd; or 5th gear if the current gear is 4th, 5th, or 6th gear.

• | The TCM forces the TCC OFF.

• | The TCM inhibits the Tap Up / Tap Down function.

### Conditions for Clearing the DTC

DTCs P1825 and P1915 are Type A DTCs.

### Diagnostic Aids

#### P1825

DTC P1825 detects an error in the decoded value for the IMS switches.

#### P1915

DTC P1915 detects an error in the decoded value for the IMS switches during an engine start.

• | 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 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.

• | Disconnecting the 14-way connector from the transmission will disable TCM communications. 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.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Transmission General Description

• | Transmission Component and System Description

• | Electronic Component Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. 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.

2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### 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 | Signal A | Signal B | Signal C | Signal 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 6/Drive 4 | LOW | LOW | LOW | HI
Drive 4 | LOW | LOW | LOW | LOW
Drive 4/Drive 3 | LOW | HI | LOW | LOW
Drive 3 | LOW | HI | LOW | HI
Drive 3/Drive 2 | HI | HI | LOW | HI
Drive 2 | HI | HI | LOW | LOW
Open | HI | HI | HI | HI
Invalid | HI | HI | HI | LOW
LOW | HI | HI | HI
HI = Ignition voltage LOW = 0 voltage

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

| Important: Before replacing the TCM, perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection .

• | Refer to Control Module References for control solenoid (w/body and TCM) valve assembly replacement, setup, and programming.

• | Perform the Service Fast Learn Adapts following all transmission related repairs.

• | For internal mode switch (IMS) replacement - perform the Manual Shift Detent Lever with Shaft Position Switch Assembly Replacement .