Codes 1 & 2 - O2 Sensor
- Turn ignition off and reset ECU. Remove alternator sense fuse in under-hood relay box for 10 seconds to reset ECU. Start engine. Check fuel pressure. See FUEL INJECTION article. Repair fuel system if not within specification. If fuel pressure is within specification, proceed to next step.
- Bring engine to operating temperature (cooling fan on). Hold engine speed at 1500 RPM for 15 minutes, without closing throttle completely during this time. Check if "CHECK ENGINE" light is on and if LED is indicating Code 1 or Code 2. If not on, problem is intermittent. Test drive and check again.
- If light is on, disconnect indicated oxygen sensor connector. Attach voltmeter to vehicle ground and 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 full closed throttle. If not within specification, replace oxygen sensor. If voltage is within specification, proceed to next step.
- Turn engine off and attach system checker harness between ECU and ECU connector. Using a voltmeter, connect negative terminal A18.
- For front oxygen sensor, attach positive voltmeter lead to connector terminal C12 and C10 for rear oxygen sensor. See Figure .
- 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 full closed throttle. If not within specification, repair wire between ECU and oxygen sensor. If within specification, substitute a known good ECU. If condition is rectified, replace original ECU.