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Notes On Fault Tree

NOTE: Numbers in list refer to circled numbers in diagnostic flow chart.
  1. Tapping on engine block simulates the noise created by detonation.
  2. The knock sensor produces an AC voltage proportional in amplitude to the 'loudness' of the knock condition.
  3. The PCM uses the knock sensor information to estimate the octane level of the fuel being used. The PCM selects a spark calibration for either 87, 90 or 93 octane value set to zero.
  4. Fuel with an octane level below 87 may cause detonation even with a properly operating engine. Engine mechanical problems such as low oil pressure, worn rod or main bearings or valve train problems may cause a knock condition.
Fig 1: Detonation Check Flow Chart
G00060926Courtesy of GENERAL MOTORS CORP.
Fig 2: Identifying Detonation Check Circuit
G00060931Courtesy of GENERAL MOTORS CORP.
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