Mazda 3 Service Manual: Precaution [ABS]

1. Any one or a combination of the ABS warning and brake system warning lights illuminates even when the system is normal.

*2 If battery voltage drops below 8 V

while vehicle speed is greater than 20 km/h {12.4 mph}

, ABS HU/CM records DTC U3003:16.

2. Precautions during servicing of ABS

The ABS is composed of electrical and mechanical parts. It is necessary to categorize malfunctions as being either electrical or hydraulic when performing troubleshooting.

a. Malfunctions in electrical system

• The ABS hydraulic unit and control module (ABS HU/CM) has an on-board diagnostic function. With this function, the ABS warning light and/or brake system warning light will illuminate when there is a problem in the electrical system. Also, past and present malfunctions are recorded in the ABS HU/CM. This function can find malfunctions that do not occur during periodic inspections. Connect the M-MDS to the DLC-2. The stored malfunctions will be displayed in the order of occurrence. To find out the causes of ABS malfunctions, use these on-board diagnostic results.

• If a malfunction occurred in the past but is now normal, the cause is likely a temporary poor connection of the wiring harness. The ABS HU/CM usually operates normally. Be careful when searching for the cause of malfunction.

• After repair, it is necessary to clear the DTC from the ABS HU/CM memory. Also, if the ABS related parts have been replaced, verify that no DTC has been displayed after repairs.

• After repairing the ABS wheel-speed sensor or ABS sensor rotor, or after replacing the ABS CM (ABS motor or ABS motor relay or solenoid valve), the ABS warning light may not go out* even when the ignition is switched to ON. In this case, drive the vehicle at a speed of 10 km/h {6.2 mph} or more

  , make sure that ABS warning light goes out, and then clear the DTC.

  * The brake system warning light also illuminates when any two wheels malfunction, or battery voltage drops below 8 V

  .

• When repairing, if the ABS related connectors are disconnected and the ignition is switched to ON, the ABS CM will mistakenly detect a fault and record it as a malfunction.

• To protect the ABS HU/CM, make sure the ignition is switched to off before connecting or disconnecting the ABS CM connector.

b. Malfunctions in hydraulic system

• Symptoms in a hydraulic system malfunction are similar to those in a conventional brake malfunction. However, it is necessary to determine if the malfunction is in an ABS component or the conventional brake system.

• The ABS hydraulic unit contains delicate mechanical parts. If foreign material enters into the component, the ABS may fail to operate. Also, it will likely become extremely difficult to find the location of the malfunction in the event that the brakes operate but the ABS does not. Make sure foreign material does not enter when servicing the ABS (e.g. brake fluid replacement, pipe removal).

Intermittent Concern Troubleshooting

Vibration method

• If malfunction occurs or becomes worse while driving on a rough road or when engine is vibrating, perform the steps below.

NOTE:

• There are several reasons why vehicle or engine vibration could cause an electrical malfunction. Some of the things to inspect are:

• Connectors not fully seated.

• Wiring harness not having full play.

• Wires laying across brackets or moving parts.

• Wires routed too close to hot parts.

• An improperly routed, improperly clamped, or loose wiring harness can cause wiring to become pinched between parts.

• The connector joints, points of vibration, and places where wiring harness pass through the firewall, body panels, etc. are the major areas to be inspected.

Inspection method for switch connectors or wiring harnesses

1. Connect the M-MDS to the DLC-2.

2. Switch the ignition to ON (engine off).

NOTE:

• If engine starts and runs, perform the following steps at idle.

3. Access PIDs for the switch you are inspecting.

4. Turn switch on manually.

5. Slightly shake each connector or wiring harness vertically and horizontally while monitoring the PID.

• If the PID value is unstable, inspect poor connection.

Inspection method for sensor connectors or wiring harnesses

1. Connect the M-MDS to the DLC-2.

2. Switch the ignition to ON (engine off).

NOTE:

• If engine starts and runs, perform the following steps at idle.

3. Access PIDs for the switch you are inspecting.

4. Slightly shake each connector or wiring harness vertically and horizontally while monitoring the PID.

• If the PID value is unstable, inspect poor connection.

Inspection method for sensors

1. Connect the M-MDS to the DLC-2.

2. Switch the ignition to ON (engine off).

NOTE:

• If engine starts and runs, perform the following steps at idle.

3. Access PIDs for the switch you are inspecting.

4. Vibrate the sensor slightly with your finger.

• If the PID value is unstable or malfunction occurs, inspect the sensor for poor connection and/or poor mounting.

Malfunction data monitor method

1. Perform malfunction reappearance test according to malfunction reappearance mode and malfunction data monitor. The malfunction cause is found in the malfunction data.

Connector terminal inspection method

1. Inspect the connection condition of each female terminal.

2. Insert a male terminal to the female terminal and inspect the female terminal for looseness.