Tach Pulse (RPM) Signal

Connect "Scan" tester to ALDL diagnostic connector. RPM should be indicated on tester when engine is cranked or running. Tach pulse (RPM reference) will be indicated as a voltage signal when a DVOM (with a minimum 10-megohm input impedance) is used to backprobe circuit No. 430 ECM terminal. If tach pulse signal is not present, vehicle will not run. For circuit and terminal reference, see appropriate schematic in NO START - ENGINE CRANKS OK.