The Vehicle Speed Sensor (VSS) is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.
Inspect the air cleaner and inlet duct. Check all engine vacuum hoses for damage, leaks, cracks, kinks and proper routing. Check Electronic Control (EC) system wiring harness for proper connections, bent or broken pins, corrosion, loose wires and proper routing. Check the powertrain control module (PCM), sensors, and actuators for physical damage.
Basic circuit checks help to minimize pinpoint test steps by providing a procedure to diagnose harness faults associated with the Electronic Engine Control (EC) System: