K 3500 Truck 4WD V8-393 6.5L DSL Turbo (1993)
Brake Signal Circuit
CIRCUIT DESCRIPTION
The normally closed brake switch supplies a 12 volts signal on CKT 420 to the PCM/TCM. The signal voltage is opened when the brakes are
applied. An incorrect brake signal can affect TCC operation.
TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test checks for voltage at brake switch.
2. This test simulates brake switch closed or brakes "OFF."
3. This test checks CKT 420 from brake switch to PCM/TCM.
4. This test opens CKT 420 and simulates brakes being applied.
DIAGNOSTIC AIDS
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Refer to "PCM/TCM Intermittent DTC(s) or Performance."
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Check customer driving habits and/or unusual traffic conditions (i.e. stop and go expressway traffic).
