Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1990LUMINA APV V6-191 3.1LREPAIR AND DIAGNOSISTECHNICAL SERVICE BULLETINSALL TECHNICAL SERVICE BULLETINSA/T - DIAGNOSING CONVERTER LOCK-UP PROBLEMSTEST # 3 - CHECKING FOR 12 VOLTS ACROSS BRAKE SWITCH
1990 Chevrolet Lumina APV V6-191 3.1L
Test # 3 - Checking For 12 Volts Across Brake Switch
1990 Chevrolet Lumina APV V6-191 3.1LSECTION Test # 3 - Checking For 12 Volts Across Brake Switch
TEST # 3
CHECK FOR 12 VOLTS AT BOTH SIDES OF THE BRAKE SWITCH
^ Check for 12 volts at both sides of the brake switch. Some GM vehicles have two electric switches at the brake pedal. One switch will have four wires and the other switch will have two wires and a vacuum hose.
IMPORTANT
Either of these switches can be used for lock-up. To avoid mis-diagnosis, check them both. If the upper switch with the vacuum hose is used, check the two wires at that switch. On the four wire lower switch, check the two wires farthest from the plunger.
^ Connect the alligator clip of your test light to ground.
^ Do not depress the brake pedal.
^ Turn the ignition "on".
^ Push the tip of your tester into one wire and the tester should light.
^ Now test the other wire and again the tester should light.
^ Depress the brake pedal and re-test. Only one wire should now be hot.
CHECK FOR 12 VOLTS AT BOTH SIDES OF THE BRAKE SWITCH
^ Check for 12 volts at both sides of the brake switch. Some GM vehicles have two electric switches at the brake pedal. One switch will have four wires and the other switch will have two wires and a vacuum hose.
IMPORTANT
Either of these switches can be used for lock-up. To avoid mis-diagnosis, check them both. If the upper switch with the vacuum hose is used, check the two wires at that switch. On the four wire lower switch, check the two wires farthest from the plunger.
^ Connect the alligator clip of your test light to ground.
^ Do not depress the brake pedal.
^ Turn the ignition "on".
^ Push the tip of your tester into one wire and the tester should light.
^ Now test the other wire and again the tester should light.
^ Depress the brake pedal and re-test. Only one wire should now be hot.
RENDER: 1.0x
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • 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.