Code 1 &/Or 2 - Oxygen (O2) Sensor

Turn off ignition. Reset ECU by removing hazard fuse in main fuse box for 10 seconds. Start engine. Check fuel pressure at fuel filter. See BASIC TESTING article. Repair fuel system if not within specification. If fuel pressure is within specification, proceed to next step.
On Civic HF and STD, 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 2000 RPM for 15 minutes without closing throttle completely during this time.
On other models, bring engine to operating temperature (cooling fan comes on). Hold engine speed at 1500 RPM (minimum) for 15 minutes, without closing throttle completely during this time.
Check if "CHECK ENGINE" light is on. If not, problem is intermittent. Test drive and check light again. If light is on, disconnect indicated O2 sensor connector. Attach voltmeter to vehicle ground and O2 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. Reconnect O2 sensor connector. Attach ECU test harness between ECU and ECU connector. See Figure . Restart and warm engine to normal operating temperature. Hold engine speed at 4000 RPM for 10 seconds and close throttle completely.
Measure voltage between ECU terminals C16 (pos.) and A 18 (neg.).
Voltage at wide open throttle or 4000 RPM should be greater than .6 volt, and less than .4 volt at closed throttle. If not within specification, repair wire between ECU and oxygen sensor(s). If within specification, substitute a known good ECU. If condition is rectified, replace original ECU.