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Home >> Cadillac >> 1990 >> Allante 4T60/ME9 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> ECM DTC EO42: Left O2 Sensor Lean >> Action Taken

Action Taken

  1. ECM turns on Service Engine Soon telltale.
  2. ECM enables canister purge.
NOTE: The following step numbers refer to circled numbers on diagnostic chart. See Fig 1 . For circuit identification, see Figure .
  1. With the oxygen sensor disconnected, parameter ED33 should remain at reference voltage (0.38 to 0.63 volts).
  2. Checking for sensor circuitry able to record rich readings. The DVOM set on volts will supply a very small current source to drive CKT 912 above 0.64 volts (rich). Similar results may be obtained by placing one finger on battery positive and another finger on oxygen sensor CKT 912 harness terminal.
  3. The ECM compares oxygen sensor signal voltage received on circuit 912 to the ground voltage on circuit 413. If the ground voltage on circuit 413 is not engine ground (battery negative), the oxygen sensor can appear falsely high or low. With the engine running, use a voltmeter to measure voltage from the oxygen sensor pin A to the ECM terminal E15. If the voltage is greater than -0.05 to +0.05 volts, repair poor ground on CKT 413 between ECM terminal E15 and engine ground.
Fig 1: Identifying ECM DTC EO42: Left O2 Sensor Lean Flow Chart
G00114224Courtesy of GENERAL MOTORS CORP.
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