Code 1, Oxygen Sensor
- Warm engine to operating temperature (cooling fan comes on). Turn off ignition. Remove "EFI/ECU" fuse in under-hood relay panel for 10 seconds to reset ECU. Remove No. 2 vacuum hose from manifold vacuum fitting. Plug fitting. See Fig 1
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- Start engine and slowly apply 13 in. Hg. Hold engine speed at 2500 RPM (minimum) for 30 seconds (late models) or 3 minutes (early models), without closing throttle completely during this time. Check if warning light is on. If not on, problem is intermittent. Check and seat connectors at sensor, battery and control unit. Test drive and check light again.
- If light is on, disconnect oxygen sensor connector. Attach voltmeter to vehicle ground and oxygen sensor connector. With engine at normal operating temperature, momentarily open throttle wide open, then close throttle.
- Voltage at wide open throttle should be greater than 6 volt, and less than .4 volt at closed throttle. If not within specifications, replace oxygen sensor. If voltage is within specifications, proceed to next step.
- Turn engine off and reconnect oxygen sensor connector. Attach system checker harness between ECU and ECU connectors. Using a voltmeter, connect negative lead to connector terminal B8.
- Attach positive voltmeter lead to connector terminal B1. Start engine and warm to operating temperature. Momentarily open throttle wide open, then close throttle. Voltage at wide open throttle should be greater than .6 volt, and less than .4 volt at closed throttle. If not within specifications, repair wire between ECU terminal B1 and oxygen sensor.
- If within specifications, hold engine speed at about 2000 RPM. If voltage does not fluctuate from less than .4 volt to greater than .6 volt, perform EACV FUNCTIONAL TEST
. If voltage does fluctuate, substitute a known good ECU. If condition is rectified, replace original ECU.
Courtesy of AMERICAN HONDA MOTOR CO., INC.