Code 1 - Oxygen Sensor
- Warm engine to normal operating temperature (until cooling fan comes on). Turn ignition off. Remove "EFI/ECU" fuse in under-hood relay panel for 10 seconds to reset ECU.
- Start engine and allow to idle for one minute. Raise engine speed to 3000 RPM. Quickly remove vacuum hoses No. 2 and No. 7 from vacuum hose manifold. Plug vacuum ports. See Fig 1
. Hold engine speed at 3000 RPM for 20 seconds. Verify if "CHECK ENGINE" light is on and if LED is flashing Code 1. If it is, go to next step. If not, problem is intermittent. Check connectors at O2 sensor, battery, and at ECU.
- Turn ignition off. Disconnect O2 sensor wire harness and connect voltmeter between O2 sensor connector and ground. Start engine. Measure voltage between O2 sensor connector and ground.
- Voltage should be greater than .6 volt at wide open throttle, and less than .4 volt at closed throttle. If not within specification, replace O2 sensor. If okay, proceed to next step.
- Turn ignition off and reconnect O2 sensor. Attach ECU test harness connector "B" between ECU and ECU connector. See Figure
. Start and warm up engine. Using a voltmeter, measure voltage between ECU terminals No.1 (pos.) and B8 (neg.).
- Momentarily open throttle wide open, then close throttle quickly. Voltage at wide open throttle should be greater than .6 volt, and less than .4 volt at closed throttle. If okay, substitute a known good ECU and recheck. If condition is rectified, replace original ECU.
- If voltage was not as specified in step 6), repair open or short circuit in White wire between ECU terminal B1 and O2 sensor.
Courtesy of AMERICAN HONDA MOTOR CO., INC.