The ABS control module receives battery voltage when the system enable relay contacts are closed. Voltage at this input provides the power source for the three DC motors and two solenoids. If the ABS control module detects a fault in this circuit, it will disable ABS operation and turn On the antilock telltale lamp.

Code 18 sets if:

Enable relay coil circuit is shorted to B+.

Code 86 could also set and the brake telltale lamp will illuminate if the rear ABS motor is not in the home position.

When attempting to diagnose an intermittent problem, use the Scan tool to review supplemental diagnostic information. The supplemental data can be used to duplicate a problem.

Select Malf History from Scan tool ABS menu.

Intermittents or opens suspected to be at the connectors can be detected by using a diagnostic service probe. Voltage can be read on wires without disconnecting any connectors.

Check the tightness of the female terminal grip with a spare male terminal.

This code will not set when a previous failure has already disabled ABS.