Mazda RX-8 Workshop Manual page 1676

b. Malfunctions in hydraulic system
Intermittent Concern Troubleshooting
Vibration method
If a malfunction occurs or becomes worse while driving on a rough road or when the engine is
vibrating, perform the following steps.
NOTE:
There are several reasons why vehicle or engine vibration could cause an electrical malfunction.
Inspect the following:
An improperly routed, improperly clamped, or loose harness can cause wiring to become pinched
between parts.
The connector joints, points of vibration, and places where wiring harnesses pass through the
firewall, body and other panels are the major areas to be inspected.
Inspection method for switch connectors or wires
1. Connect the M-MDS to the DLC-2.
* The BRAKE system warning light also illuminates when there is any rear
wheel deformation.
When repairing, if the ABS related connectors are disconnected and the
ignition switch is turned to the ON position, the ABS HU/CM will mistakenly
detect a fault and record it as a malfunction.
To protect the ABS HU/CM, make sure the ignition is off before connecting
or disconnecting the ABS HU/CM connector.
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 gets 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).
Connectors not fully seated.
Wire harnesses not having full play.
Wires laying across brackets or moving parts.
Wires routed too close to hot parts.