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HOMESERVICE MANUALSGMC1991G 3500 1 TON VAN V8-379 6.2L DSLREPAIR AND DIAGNOSISTRANSMISSION AND DRIVETRAINAUTOMATIC TRANSMISSION/TRANSAXLETESTING AND INSPECTIONCOMPONENT TESTS AND GENERAL DIAGNOSTICSBRAKE SIGNAL CIRCUIT CHECK
1991 GMC G 3500 1 Ton Van V8-379 6.2L DSL

Brake Signal Circuit Check

1991 GMC G 3500 1 Ton Van V8-379 6.2L DSLSECTION Brake Signal Circuit Check

Brake Signal Circuit:





Circuit Description:
The normally closed brake switch supplies a 12 volt signal on CKT 420 to the PCM/TCM. The signal voltage is removed when the brakes are applied. An incorrect brake signal may affect TCC operation.


Brake Signal Diagnostic Chart:





Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checks for voltage at brake switch.

2. This test simulates brake switch closed or brakes "OFF".

3. Checks CKT 420 from brake switch to PCM/TCM.

4. This opens CKT 420 and simulates brakes being applied.


Diagnostic Aids:
^ See "Diagnosis of Intermittents"
^ Check customer driving habits and/or unusual traffic conditions (i.e. stop and go expressway traffic).
RENDER: 1.0x

NO RELATED

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.