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 MANUALSCHEVROLET1994C 2500 SUBURBAN 2WD V8-350 5.7LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSVEHICLE SPEED SENSOR SIGNAL BUFFERDESCRIPTION AND OPERATION
1994 Chevrolet C 2500 Suburban 2WD V8-350 5.7L
Vehicle Speed Sensor Signal Buffer: Description and Operation
1994 Chevrolet C 2500 Suburban 2WD V8-350 5.7LSECTION Description and Operation
DESCRIPTION
The Speedometer/Odometer is electronic and does not require a speedometer cable. The speedometer receives a vehicle speed signal from the Vehicle Speed Sensor Buffer. The Vehicle Speed Sensor Buffer receives an AC voltage signal from the transmission mounted Vehicle Speed Sensor (VSS).
The VSS generates a signal that indicates the speed of the vehicle. The Signal is processed by the solid-state Vehicle Speed Sensor Buffer to supply inputs to the Powertrain Control Module (PCM), the Cruise Control Module and the Speedometer.
OPERATION
The VSS is mounted in the transmission. A toothed rotor rotates near a coil, producing voltage pulses in the coil.
The rotor that is attached to the transmission turns four times faster than a standard speedometer cable. The coil near the rotor generates 40 pulses per revolution.
The frequency of the AC voltage coming from this coil depends on the vehicle speed. As the speed increases, so does the number of voltage pulses per second.
The Vehicle Speed Sensor Buffer takes the voltage pulses from the sensor and uses them to close three solid-state output switches. Each output terminal is switched to ground at a rate that is proportional to the speed of the vehicle. The Speedometer is switched by the primary rate of the VSS. The PCM and the Cruise Control use a lower frequency. Their input switches are operated by a circuit that divides the sensor frequency by two.
Different Vehicle Speed Sensor Buffers are used to match the vehicle final drive ratio to the components.
The Speedometer/Odometer is electronic and does not require a speedometer cable. The speedometer receives a vehicle speed signal from the Vehicle Speed Sensor Buffer. The Vehicle Speed Sensor Buffer receives an AC voltage signal from the transmission mounted Vehicle Speed Sensor (VSS).
The VSS generates a signal that indicates the speed of the vehicle. The Signal is processed by the solid-state Vehicle Speed Sensor Buffer to supply inputs to the Powertrain Control Module (PCM), the Cruise Control Module and the Speedometer.
OPERATION
The VSS is mounted in the transmission. A toothed rotor rotates near a coil, producing voltage pulses in the coil.
The rotor that is attached to the transmission turns four times faster than a standard speedometer cable. The coil near the rotor generates 40 pulses per revolution.
The frequency of the AC voltage coming from this coil depends on the vehicle speed. As the speed increases, so does the number of voltage pulses per second.
The Vehicle Speed Sensor Buffer takes the voltage pulses from the sensor and uses them to close three solid-state output switches. Each output terminal is switched to ground at a rate that is proportional to the speed of the vehicle. The Speedometer is switched by the primary rate of the VSS. The PCM and the Cruise Control use a lower frequency. Their input switches are operated by a circuit that divides the sensor frequency by two.
Different Vehicle Speed Sensor Buffers are used to match the vehicle final drive ratio to the components.
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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.