C0191

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

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Diagnostic System Check - Vehicle

Circuit/System Description
The electronic brake control module (EBCM) supplies a 5-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 5-volt reference to the longitudinal accelerometer is less than 4.4 volts or greater than 5.6 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 7,200 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
ABS Schematics

Connector End View Reference
ABS Connector End Views

Electrical Information Reference
^ Circuit Testing
^ Connector Repairs
^ Testing for Intermittent Conditions and Poor Connections
^ Wiring Repairs

Scan Tool Reference
Scan Tool Data List

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, check for voltage between 4.4 and 5.6 on the LNG rate sensor 5-volt reference circuit.
^ If the voltage is above 5.6 volts, test for a short to power on the LNG rate sensor circuit.
^ If voltage is below 4.4, test for an open or a short to ground on the LNG rate sensor circuit.
^ If voltage is above 5.6 or below 4.4 and a LNG rate sensor 5-volt reference circuit fault can not be found, replace the EBCM/brake pressure modulator valve (BPMV) assembly.

2. Turn OFF the ignition. At the longitudinal accelerometer harness connector, connect a test lamp between the LNG low reference circuit and battery positive voltage. If the LNG low reference circuit is good the test lamp will illuminate.
^ If the test lamp does not illuminate check for an open in the LGN low reference circuit or.
^ If the test lamp does not illuminate and a LGN low reference circuit fault can not be found, replace the EBCM/BPMV assembly.

3. Connect a 3-amp fused jumper wire between the LNG rate sensor 5-volt reference circuit and the longitudinal accelerometer signal circuit. 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 a longitudinal accelerometer signal circuit fault can not be found, replace the EBCM/BPMV assembly.

Repair Instructions

Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

^ Yaw Rate Sensor/Lateral and Longitudinal Accelerometer Replacement
^ Control Module References for EBCM and BPMV replacement, setup, and programming