Circuit Description

The ECM supplies and monitors 12-volt signal on circuit No. 437. Circuit No. 437 connects Vehicle Speed Sensor (VSS), that alternately grounds circuit No. 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile, and the ECM calculates vehicle speed based on time between "pulses".

"SCAN" tester reading should closely match speedometer reading with drive wheels turning.