Aisin AY6 Manual Transmission
DTC P0502
Circuit Description
Vehicle speed information is provided to the engine control module (ECM) by the vehicle speed sensor (VSS). The VSS consists of a hall-effect sensor mounted to the transmission case which interfaces with a rotor pressed onto the transmission output shaft. The hall-effect sensor contains a permanent magnet and a semiconductor plate to which ignition voltage is applied. As the output shaft spins, the rotor directs the field of the permanent magnet either toward or away from the plate. When the ignition is ON and the magnetic field is directed away from the plate, electrons are evenly distributed across the plate. When the rotor directs the field toward the plate, the electrons are redistributed unevenly across the front and back of the plate. The uneven distribution causes a voltage to be produced across the plate. The VSS produces a frequency signal that is proportional to vehicle speed. The ECM converts the VSS signal to vehicle speed, displayed on the scan tool in miles per hour and kilometers per hour. The ECM also uses the VSS signal to generate the 4,000 pulses per mile vehicle speed signal used by the instrument cluster.
When the ECM detects no vehicle speed for a specified length of time while other sensors indicate that the vehicle is moving, DTC P0502 sets. DTC P0502 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Voltage
Conditions for Running the DTC
* The engine speed is greater than 1,800 RPM for 3 seconds.
* The engine coolant temperature (ECT) is greater than 40°C (104°F).
Conditions for Setting the DTC
The VSS indicates a speed of less than 0 km/h (0 mph) for 4 seconds continuously or 50 seconds cumulative.
Action Taken When the DTC Sets
* The ECM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
* The ECM disables Cruise Control.
* The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records.
* The ECM stores DTC P0502 in ECM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
Conditions for Clearing the MIL/DTC
* The ECM turns OFF the MIL during the third consecutive trip in which the diagnostic runs and passes.
* A scan tool can clear the MIL/DTC.
* The ECM clears the DTC from ECM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
* The ECM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the ECM.
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Step 8 - Step 19:
