Brakes - Warning Lamp ON

BULLETIN NUMBER ISSUE DATE GROUP
SB86-09-003 August 8, 1986 BRAKES
VEHICLES AFFECTED

P'UP (KB) and Trooper II (KT) models with C223 turbo diesel engine.

SERVICE INFORMATION

The brake warning light on the instrument panel may light under the following conditions:
a. The engine is at idle or near idle AND
b. The brakes are applied frequently during a short time period ("pumped").

The warning light is being turned on by the low vacuum warning switch and will usually turn off within a few seconds. This situation is normal, even when all parts of the brake vacuum system are in good working condition.

The procedures in this Service Bulletin can be used along with the information in the appropriate Workshop Manual to check the brake vacuum system and make certain that it is operating to specifications.

SERVICE PROCEDURE

1. Check the performance of the vacuum pump as described in SB86-04-006.
2. To test the low vacuum waming switch, remove it from the brake Master Vac unit as described in the appropriate Workshop Manual.

3. Connect an ohmmeter or self-powered test lamp between the switch terminal and the switch body. With no vacuum applied to the switch, it should be closed; the ohmmeter should show no resistance or the test lamp should light.

4. Connect a hand-held vacuum pump to the sensing end of the switch.

5. Apply vacuum to the switch. At about 12 in. Hg (300 mm Hg), the switch should open. The ohmmeter should show infinite resistance or the test lamp should go out.

6. If the vacuum pump and low vacuum warning switch meet the test specifications, and the rest of the brake system is in good working condition as outlined in the Workshop Manuals, then the situation described under "Service Information" can be considered normal vehicle operation.