Code 43 - ESC Retard Signal Too Low: Notes

The Knock sensor detects engine detonation (vibration). The ECM will retard electronic spark timing based signal being received. The circuitry within the knock sensor causes ECM 5 volts to be reduced so that under a knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal which rides on the 2.5 DC voltage. The amplitude and signal frequency are dependent upon knock level. ECM performs 2 tests on this circuit to determine if operation is correct. If either of 2 test fail, a Code 43 will be set. The following are test procedures performed by ECM:

• An indication of knock for 3.67 seconds greater than a 3.9 second interval with engine running.
• ECM terminal "YD9" voltage is either greater than about 3.75 volts (indicating an open circuit No. 496), or less than about 1.25 volts (indicating circuit No. 496 is shorted to ground) for 5 seconds or more.
  NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. If conditions for test, as described above, are being met, "Scan" tester will always indicate "YES" when knock signal position is selected. If an audible knock is heard from engine, repair internal engine problem so that knock will not take place at idle.
  2. If tapping on engine lift hook does not produce a knock signal, try tapping engine closer to sensor before proceeding.
  3. ECM has a 5 volt signal through the pull-up resistor, which should be present at knock sensor terminal.
  4. This test will determine if knock sensor or ESC portion of MEM-CAL is at fault.