For 1990-2009 cars

### Circuit Description

The ignition 1 circuit supplies 12 volts 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 (0 ft/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. The harder the acceleration or deceleration, the greater the change in signal voltage.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0191 All Wheel Drive (AWD)/Four Wheel Drive (4WD) Reference Accelerometer Circuit

### Conditions for Running the DTC

Both of the conditions listed below may be required to set the DTC.

• | The ignition is ON.

• | The vehicle is accelerated rapidly to a speed greater than 11 km/h (7 mph) before decelerating rapidly to a stop.

### Conditions for Setting the DTC

Any of the following conditions may cause the DTC to set.

• | Open longitudinal accelerometer circuitry is detected.

• | Shorted longitudinal accelerometer circuitry is detected.

• | An erratic longitudinal accelerometer signal is detected.

• | The electronic brake control module (EBCM) detects that the longitudinal accelerometer sensor signal does not correspond with signals from other sensors.

### Action Taken When the DTC Sets

• | The EBCM disables the Antilock Brake System (ABS).

• | The ABS indicator turns ON.

• | The ABS fault message is displayed.

### Conditions for Clearing the DTC

The conditions for setting the DTC are no longer present and you use the scan tool Clear DTCs function.

### Diagnostic Aids

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to Testing for Electrical Intermittents , Testing for Intermittent Conditions and Poor Connections , Wiring Repairs , and Connector Repairs .

### Diagnostic Aids

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to the following:

• | Testing for Electrical Intermittents

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

• | Connector Repairs

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Antilock Brake System Schematics Connector End View Reference: Antilock Brake System Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Use the scan tool to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Turn OFF the ignition.
2. Disconnect the longitudinal accelerometer harness connector. Refer to Longitudinal Accelerometer Replacement .
3. Turn ON the ignition.
4. Connect a test lamp between the ignition 1 circuit and a good ground.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 9

4 |

1. Select the Antilock Brake System (ABS) Data Display function on the scan tool.
2. Observe the Longitudinal Accelerometer Sensor Input on the scan tool.

Is the Longitudinal Accelerometer Sensor Input voltage less than the specified value?

0.6 V

Go to Step 5

Go to Step 13

5 |

1. Connect a 3-amp fused jumper wire between the ignition 1 circuit and the LNG rate signal circuit. Refer to Using Fused Jumper Wires .
2. Observe the Longitudinal Accelerometer Sensor Input on the scan tool.

Is the Longitudinal Accelerometer Sensor Input voltage greater than the specified value?

4.75 V

Go to Step 7

Go to Step 6

6 | Test the LNG rate signal circuit for the following conditions.

• | An open

• | A high resistance

• | A short to ground

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

7 | Use a DMM to measure the voltage between the ignition 1 voltage circuit and the longitudinal accelerometer ground circuit. Does the voltage measure greater than the specified value? | 11 V | Go to Step 10 | Go to Step 8
8 | Test the longitudinal accelerometer ground circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 11
9 | Repair the open in the ignition 1 circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 15 | --
10 |

1. Inspect for poor connections at the harness connector of the longitudinal accelerometer. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
2. Ensure the longitudinal accelerometer is mounted properly.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

11 | Inspect for poor connections at the harness connector of the electronic brake control module (EBCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14
12 | Replace the longitudinal accelerometer. Refer to Longitudinal Accelerometer Replacement . Did you complete the replacement? | -- | Go to Step 15 | --
13 | Test the LNG rate signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14
14 | Replace the EBCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 15 | --
15 |

1. Use the scan tool to Clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

Go to Step 3

System OK