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Home >> Chevrolet >> 1988 >> Spectrum Express >> Repair and Diagnosis >> Engine Performance >> System >> Feedback Carburetor System >> Trouble Shooting >> Trouble Codes >> CODE 55 (Faulty O2 Sensor or ECM)
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CODE 55 (Faulty O2 Sensor or ECM)

  1. Check for corrosion at ECM connector. Disconnect ALDL test terminal and O2 sensor, note "Check Engine" light with engine idling for less than one minute. If light is off, go to step 3). If light is on, stop engine and turn ignition on. Check voltage from ECM connector terminal No. 7 to 20.
  2. If voltage is greater than 4 volts, go to step 3). If voltage is less than 4 volts, check for ground in ECM connector terminal No. 7 wiring, including TPS. If not grounded or shorted, replace ECM.
  3. With ignition on and engine stopped, disconnect O2 sensor. Check voltage from ECM connector terminal No. 3 to ground. If voltage is greater than 1 volt, go to step 4). If voltage is less than 1 volt, check for intermittent ground in ECM connector terminal No. 7 harness, including TPS. If circuit is okay, replace O2 sensor.
  4. Turn ignition off and disconnect ECM. With ignition on, check voltage from ECM connector terminal No. 3 to ground. If voltage is greater than 1 volt, check for short in ECM connector terminal No. 3 circuit. If voltage is less than 1 volt, check for open circuit from ECM connector terminal No. 20 to ground. If not open, replace ECM.
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