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 Descriptor

DTC C0191 00: Four Wheel Drive (4WD) Reference Accelerometer Circuit

### Circuit/System Description

The electronic brake control module (EBCM) supplies a 12-volt reference to the longitudinal accelerometer. When the vehicle is not moving, or is being driven at a constant steady speed, longitudinal acceleration is 0 m/sec/sec, and the longitudinal accelerometer signal voltage is very near 2.5 volts. This is referred to as longitudinal accelerometer bias voltage. Vehicle acceleration or deceleration causes the longitudinal accelerometer signal voltage to increase or decrease.

### Conditions for Running the DTC

• | The ignition is ON.

• | Ignition voltage is greater than 8 volts.

### Conditions for Setting the DTC

• | The 12-volt reference to the longitudinal accelerometer is less than 11.4 volts or greater than 12.6 volts.

• | The longitudinal accelerometer output is greater than 1.5 g or less than -1.5 g for 1.2 seconds.

• | The longitudinal accelerometer output is greater than 1.5 g or less than -1.5 g for 7200 ms periods during the same ignition cycle.

• | The longitudinal accelerometer output does not change when the vehicle decelerates from 30 km/h (19 mph) to 0 km/h. If the condition occurs 16 consecutive times, the DTC is set.

### Action Taken When the DTC Sets

• | The EBCM disables the Antilock Brake System (ABS)/Traction Control System (TCS) for the duration of the ignition cycle.

• | The ABS indicator turns ON.

• | The driver information center (DIC) displays the ABS FAULT message.

• | The DIC displays the TRACTION FAILED message.

### Conditions for Clearing the DTC

• | The condition for setting the DTC is no longer present and the DTC is cleared with a scan tool.

• | The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

### Reference Information

#### Schematic Reference

Antilock Brake System Schematics

#### Description and Operation

ABS Description and Operation

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

With scan tool installed drive the vehicle in a straight line at a speed greater than 30 km/h (19 mph) and decelerate the vehicle to a stop several times. The scan tool Longitudinal Accelerometer Sensor Signal parameter should show a change in M/S² output in sequence to the vehicle deceleration.

### Circuit/System Testing

1. Turn OFF the ignition. Disconnect the longitudinal accelerometer harness connector. Turn ON the ignition. With a DMM, verify voltage between 11.4 and 12.6 on the LNG rate sensor terminal 1 12-volt reference circuit.

⇒ | If voltage is below 11.4, test for an open or a short to ground on the LNG rate sensor circuit. If the circuit tests normal, replace the EBCM assembly.

2. Turn OFF the ignition. At the longitudinal accelerometer harness connector, connect a test lamp between the LNG low reference circuit terminal 3 and battery positive voltage. Verify the test lamp illuminates.

⇒ | If the test lamp does not illuminate check for an open in the LGN low reference circuit. If the circuit tests normal, replace the EBCM assembly.

3. Connect a 3-amp fused jumper wire between the LNG rate sensor 12-volt reference circuit terminal 1 and the longitudinal accelerometer signal circuit terminal 2. Turn ON the ignition and observe the longitudinal accelerometer parameter.

⇒ | If the scan tool displays greater than 1.5g, replace the longitudinal position sensor.

⇒ | If the scan tool displays less than 1.5g, test for an open or short to ground on the longitudinal accelerometer signal circuit. If the circuit tests normal, replace the EBCM assembly.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for EBCM/BPMV replacement, setup, and programming