GM 12382860 Sensor,Vehicle Speed

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The checking procedures for various engine sensors and components are as follows: The engine coolant temperature (ECT) sensor is a thermistor that changes resistance with temperature, and a failure in the circuit can trigger trouble codes. To check it, measure the resistance while cold and warm, and ensure the reference voltage from the PCM is around 5.0 volts. The manifold absolute pressure (MAP) sensor monitors intake manifold pressure changes and varies its voltage output accordingly. Check the reference voltage and signal voltage with the ignition on and engine off, and observe voltage changes as the engine's vacuum changes. The intake air temperature (IAT) sensor acts as a thermistor, and you can measure its resistance at different temperatures to ensure it changes as expected. Also, monitor the IAT sensor using a scan tool to verify its performance. The oxygen sensor in the exhaust monitors oxygen content, and you can check its millivolt signal while the engine warms up. Inspect the oxygen sensor heater and ensure it receives proper voltage. The vehicle speed sensor (VSS) provides speed data to the PCM and can be checked for reference voltage. The camshaft sensor and crankshaft sensor, depending on the engine type, should be checked for resistance and proper signal output. Finally, the knock sensors detect engine knock and should be checked for reference voltage and resistance. If any component fails these checks, replacement may be necessary.

The VSS signal is used by the ECM/PCM for various engine and transmission control functions, as well as driving the speedometer on the instrument panel.

The Vehicle Speed Sensor (VSS) is a permanent magnet generator mounted on the transmission. It is triggered by a toothed rotor on the transmission output shaft, producing an AC voltage that is proportional to vehicle speed. This signal is used by the ECM/PCM for various engine and transmission control functions, as well as driving the speedometer on the instrument panel. If the VSS is defective, it can cause driveability and transmission problems. To check the VSS operation, raise the vehicle and locate the sensor. Check the terminals and wires for any looseness or breaks, and repair as necessary. Back probe the two wire terminals of the VSS connector and connect a voltmeter set on the AC volts scale. With the ignition key on and the engine off, rotate one rear tire while monitoring the voltmeter. The sensor should produce a minimum of 0.5 volts, increasing as the transmission output shaft rotates faster. Turn off the ignition key and disconnect the electrical connector from the sensor. Use an ohmmeter to measure the resistance across the two terminals, which should be approximately 1,000 to 3,000 ohms at 68-degrees F. If the test results are incorrect, replace the VSS. To replace the sensor, raise the vehicle and disconnect the electrical connector. Remove the mounting bolt and withdraw the VSS from the transmission case. Replace the sensor O-ring and then reinstall the VSS, following the reverse of the removal process.

If any component fails these checks, replacement may be necessary.

The vehicle speed sensor (VSS) provides speed data to the PCM. To check it, you can check for reference voltage.

The manifold absolute pressure (MAP) sensor monitors intake manifold pressure changes and varies its voltage output accordingly. To check it, you should check the reference voltage and signal voltage with the ignition on and engine off, and observe voltage changes as the engine's vacuum changes.