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C-5, Electronic Spark Control (ESC) Circuit (Except 2.5L, 4.3L Turbo & Vehicles With 4L80-E Transmission)

  1. An open or short circuit on ESC wire to ECM will cause a loss of 12-volt ESC controller signal. This will cause ECM to fully retard ignition timing.
  2. If a Scan tester is available, connect it to the ALDL connector. Using a metal object, tap on engine next to knock sensor and note knock parameter. Knock should be indicated on Scan tester.
  3. If a Scan tester is not available, backprobe ECM ESC signal terminal with a DVOM. With engine idling, 812 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at ECM terminal should drop to zero volts, and return when knock signal ceases.
  4. If signal does not respond as described, check knock sensor signal to controller signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur. Also, see KNOCK SENSOR under ENGINE SENSORS & SWITCHES.
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