GMC 12382860 Sensor,Vehicle Speed

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Various engine sensors and components have checking procedures,the engine coolant temperature (ECT) sensor is a thermistor that changes resistance with temperature, and a failure in the circuit can cause trouble codes. The resistance should be measured when cold and warm while ensuring reference voltage from PCM is around 5.0 volts for the verification. Manifold Absolute Pressure (MAP) Sensor monitors changes in intake manifold pressure then varies its voltage output accordingly. Look at the reference voltage and signal voltage with the ignition on and engine off, and observe voltage changes as the engine's vacuum changes. Intake Air Temperature (IAT) Sensor acts as a thermistor where you can measure its resistance at different temperatures to make sure it changes as expected. Also, use a scan tool to monitor the IAT sensor for performance. The oxygen sensor in exhaust detects oxygen content which you can check its millivolt signal while warming up your engine. Check whether the oxygen sensor heater has correct voltage or not. Vehicle Speed Sensor (VSS) provides speed data to PCM which can be checked for reference voltage. Depending on the type of engine, Camshaft Sensor and Crankshaft Sensor should be checked for resistance and proper signal output. Finally, Knock Sensors detect engine knock which should be checked for reference voltage and resistance. If any component fails these checks, replacement may be necessary.

A toothed rotor on the transmission output shaft causes the Vehicle Speed Sensor (VSS), which is a permanent magnet generator mounted on the transmission, to produce an AC voltage. The ECM/PCM uses this signal for different engine and transmission control functions as well as driving the speedometer on the instrument panel. Driveability and transmission problems can result from a defective VSS. To check the VSS operation, raise the vehicle and locate the sensor. Check for any looseness or breaks in terminals and wires and repair if necessary. Back probe the two wire terminals of the VSS connector and connect a voltmeter set on AC volts scale. With ignition key ON, engine OFF, rotate one rear tire while monitoring voltmeter. As minimum as 0.5 volts should be produced by the sensor with increasing speed of rotation of transmission output shaft. Turn off ignition key and disconnect electrical connector from sensor. Measure resistance across two terminals using ohmmeter, which should be approximately 1,000 to 3,000 ohms at 68 degrees F.Temperature If test results are incorrect replace VSS.Replacing means raising vehicle, disconnecting electrical connector, removing mounting bolt then drawing VSS from transmission case.Replace sensor O-ring.Then reinstall VSS back following opposite steps used during removal.

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.

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.