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 P081A: Starter Inhibit Circuit Low Voltage
DTC P081B: Starter Inhibit Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Starter Inhibit Circuit | P081A | P081A | P081B | --

### Circuit/System Description

The transmission range (TR) switch is an integral part of the transmission control module (TCM). As the gear range selector lever is moved, the state of the Starter Inhibit Circuit may change, causing the circuit to open or close. An open circuit indicates a drive range and a low voltage signal, 0 volts, at the engine control module (ECM). A closed circuit indicates PARK or NEUTRAL and a high voltage, 12 volts, signal at the ECM.

The ECM uses the Starter Inhibit circuit status from the TCM in order to enable starter operation.

### Conditions for Running the DTC

• | Start Lock Driving voltage is within 6.0-16.0 volts.

• | Ignition voltage is greater than 6.5 volts.

### Conditions for Setting the DTC

#### P081A

The ECM detects "ON" signal from the Starter Inhibit circuit while the TCM is commanding the Starter Inhibit circuit "OFF" for 0.5 seconds.

#### P081B

The ECM detects "OFF" signal from the Starter Inhibit Circuit while the TCM is commanding the Starter Inhibit Circuit "ON" for 0.5 second.

### Action Taken When the DTC Sets

None

### Conditions for Clearing the DTC

DTC P081A and P081B are Type A DTCs.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

• | Electrical Center Identification Views

• | Component Connector End Views

• | Splice Pack Connector End Views

• | Inline Harness Connector End Views

#### 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

• | Diagnostic Trouble Code (DTC) List - Vehicle

#### Scan Tool Reference

Control Module References for scan information.

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool.
2. Record Freeze Frame and Failure Records.
3. Clear DTCs.
4. Operate the vehicle under the conditions observed in the Failure Records.
5. Observe the DTC information with the scan tool. Verify that the DTC does not set.

### Circuit/System Testing

1. Engine ON, with the scan tool, observe the TR Sw. parameter while selecting each transmission range: P, R, N, D5, D4, D3, D2, and D1. Each selected transmission range should correspond to the correct scan tool PNP Switch parameter displayed.

⇒ | If not equal to the specified range, Test the Starter Inhibit Circuit for a short to ground, an open/high resistance, or a short to voltage. If the circuit test normal, replace the TCM.

2. With the scan tool, observe the PNP Switch parameter (Engine Electrical/Theft Data) while selecting each transmission range: P, R, N, D5, D4, D3, D2, and D1. Each selected transmission range should correspond to the correct scan tool PNP Switch parameter displayed (Park/Neutral/In Gear).

⇒ | If not equal to the specified range, test the Starter Inhibit Circuit for a short to ground, an open/high resistance, or a short to voltage. If the circuit tests normal, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.