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Home >> Honda >> 1991 >> Civic EX, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Codes >> Code 1 - O2 Sensor

Code 1 - O2 Sensor

  1. Turn ignition off. Reset ECU by removing ECU fuse in main fuse/relay block for 10 seconds. Check fuel pressure regulator. See SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE Section. Repair or replace as necessary. Warm engine to normal operating temperature (cooling fan comes on).
  2. On 1.5L, block rear wheels, and set parking brake. Jack up front of vehicle, and support with safety stands. Place transmission in 2nd gear, and run engine at 2400 RPM for 15 minutes without closing throttle completely.
  3. On 1.6L, bring engine to operating temperature (cooling fan comes on). Hold engine RPM at 1500 RPM (minimum) for 15 minutes without closing throttle completely.
  4. On all models, check if CHECK ENGINE light is on and if LED indicates Code 1. If light is not on and Code 1 is not present, problem is intermittent. Test drive, and check light again. If light is on and Code 1 is present, inspect for poor connection and loose ground at thermostat housing. Repair as necessary. If connections and wires are okay, go to next step.
  5. Disconnect O2 sensor connector. Connect voltmeter to vehicle ground and O2 sensor connector. With engine at normal operating temperature and while watching voltmeter, hold engine speed at 4000 RPM for 10 seconds and then release throttle completely.
  6. Voltage should be greater than .6 volt at wide open throttle and less than .4 volt at closed throttle. If voltage is not as specified, replace O2 sensor. If voltage is within specifications, proceed to next step.
  7. Turn ignition off. Reconnect O2 sensor connector. Attach ECU Test Harness (07999-PD6000A ) between ECU and ECU connector. See Figure . Connect voltmeter between ECU terminals A18 (-) and C16 (+). See Figure . Restart and warm engine to normal operating temperature. Hold engine speed at 4000 RPM for 10 seconds, and then close throttle completely.
  8. Voltage should be greater than .6 volt at wide open throttle or 4000 RPM and less than .4 volt at closed throttle. If voltage is not as specified, repair short or open in White wire between ECU and O2 sensor. If voltage is within specifications, substitute a known good ECU. If condition is corrected, replace original ECU.
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