3.1L Engine

ECM applies and monitors a 12-volt signal on circuit No. 437 to Vehicle Speed Sensor (VSS). VSS is connected to speed sensor buffer which alternately grounds and opens circuit No. 437 when wheels are turning. This pulsing action takes place about 2000 times per mile. The voltage level and pulses increase with vehicle speed. The ECM converts the pulsing voltage to MPH. The ECM uses VSS information in calculations to determine vehicle adjustments. Scan tester reading should closely match speedometer reading when wheels are turning.

1. A Code 24 sets when MPH is less than 2 MPH, transmission is not in Park or Neutral, engine speed is greater than 1400 RPM, TPS is greater than 5 percent, circuit No. 437 voltage is constant and all of these conditions are met for 30 seconds. These conditions are met during a road load deceleration.
2. A steady 8-12 volts at ECM connector indicates VSS circuit is open or speed sensor is faulty. A voltage of less than one volt at IP connector indicates circuit No. 437 wire is shorted to ground. Disconnect vehicle speed sensor connector. If voltage is now greater than 10 volts, vehicle speed sensor buffer is faulty. If voltage remains less than 8 volts, circuit is grounded. If circuit is not grounded, check for faulty ECM connector or ECM. Before replacing the ECM, PROM should be checked for correct application.