DTC 1-4-2 Brake Light Switch, Open Circuit

DESCRIPTION
The brake light switch tells the control module when the brakes are applied, enabling the ABS system to react quickly. If the brake light switch fails to indicate that braking has started, the control module will still detect this from changes in speed signals from the wheel sensors, but subject to some delay.

CONDITIONS FOR DTC
The control module compares with its reference voltage to check that the brake lights are intact. When the ABS system cuts in, it also checks that the brake light switch is working.

NOTE: If the brake light bulbs or the connection from them to the control module is broken, the control module will post DTC 1-4-2.

SYMPTOMS
ABS warning light does not come on. ABS system working.

SOURCES OF FAULT
^ Blown fuse 11/27.
^ Brake light bulbs broken.
^ Open-circuit in lead between brake light bulbs and control module.
^ Faulty brake light switch.

CHECKING BRAKE LIGHT
1. Ignition off.
2. Check that brake light fuse is intact. fuse 11/27.
3. Ignition on.
4. Push brake pedal down and check that brake lights come on.
5. If lights do not come on, go to Checking voltage.

CHECKING VOLTAGE
1. Ignition off.
2. Connect a voltmeter across test box terminals # 20 (0 volts) and # 25.
3. Ignition on.
4. Push brake pedal down.

NOTE: Voltmeter should read battery voltage (approx. 12 volts) when brake light switch trips, at the same time as the brake lights come on.

IF READING IS INCORRECT; CHECKING LEAD RESISTANCE
1. Ignition off.
2. Disconnect battery positive lead.
3. Connect an ohmmeter between positive battery lead and test box # 25.
4. Ohmmeter should read approx. 0 ohms when brake light switch trips.

NOTE: Ohmmeter reading is infinite when brake light switch trips:

OPEN-CIRCUIT OR FAULT IN BRAKE LIGHT SWITCH
ACTION:
^ Repair open-circuit in lead or replace brake light switch.
^ Replacing brake light switch.

NOTE: Check DTCs after action.