Circuit Test C2 - Exhaust Gas/Oxygen (Ego) Sensor

Fig 1: EGO Sensor Circuits

NOTE: Enter this test only when a Code 15 is displayed during the QUICK TEST procedure. This test will not diagnose fuel system problems. To prevent replacement of good components, be aware that the following non-EEC items may be faulty: fuel quality, intake air cleaner and duct, fuel delivery system or ignition system. This test is intended to diagnose only the following: EGO sensor, EGO circuits or ECA.

1. Checking System Integrity  - Visually check all wiring, harnesses, connectors and components for evidence of damage, overheating, shorting or looseness. If a fault is found, repair as necessary. If no faults are found, go to next step.
2. Checking EGO Sensor Output Voltage  - Warm up engine and run at idle. Set VOM on 5-volt scale. Disconnect EGO sensor. Measure voltage between EGO sensor connector (sensor side) and ground. Increase engine speed to 4000-4500 RPM until voltmeter reads 0.7 volt. Rapidly decrease and increase engine speed while reading voltmeter. When engine speed is decreasing, voltage should be 0-0.4 volt. When engine speed is increasing, voltage should be 0.5-1.0 volt. If voltage is within specification, go to step 5). If voltage is not to specification, go to next step.
3. Isolating Open Circuit In EGO Sensor  - With key off, disconnect EGO sensor. Inspect "BK" wire from EGO sensor connector for possible opens. If EGO sensor wire is okay, go to next step. If not, repair wire or replace sensor as necessary.
4. Isolating Short In EGO Circuit  - With key off, disconnect EGO sensor. Set VOM on 200k-ohm scale. Connect VOM between EGO sensor connector (sensor side) and ground. If resistance is greater than 10k ohms, replace EGO sensor. If resistance is not greater than 10k ohms, repair short in EGO sensor wire or replace EGO sensor as required.
5. Checking EGO Sensor Sensitivity  - Ensure EGO sensor is connected. Start engine. This step requires Ford Motor Co. SUPER STAR II Tester and Adapter Cable (007-00036). Connect adapter cable to Self-Test Output (STO) connector and ground. Leave Self-Test Input (STI) connector open (not grounded). Warm up engine and run at idle. Increase engine speed to 2500 RPM. If monitor light on tester flashes 8 times in 10 seconds, go to step 8). If not, go to next step.
6. Checking EGO Sensor Circuit  - With key off, install breakout box. Leave ECA and EGO sensor disconnected. Set DVOM on 200-ohm scale. Measure resistance between EGO sensor connector (harness side) and test pin No. 29 at breakout box. If resistance is greater than 10 ohms, repair open circuit and reconnect EGO sensor. If resistance is 10 ohms or less, go to next step.
7. Checking EGO Sensor Circuit  - With key off, install breakout box. Leave ECA and EGO sensor disconnected. Set VOM on 200k-ohm scale. Measure resistance between test pin No. 29 and test pins No. 1, 26, 37 and 49. If any resistance is less than 10k ohms, repair short in EGO sensor circuit to VPWR, VREF, KAPWR or ground as necessary. If none of the resistance readings are 10k ohms or less, replace EGO sensor.
8. Checking ECA Input Voltage  - Install breakout box, leave ECA connected. Set VOM 5-volt scale. Warm engine to normal operating temperature. Measure voltage between test pins No. 29 and 49 at breakout box wile increasing and decreasing engine speed between 1500 and 4000 RPM. If voltage changes between 0.5 volt and 1.0 volt, replace ECA. If voltage does not change as specified, inspect ECA and ECA No. 2 connector for damage, looseness or corrosion. Repair as necessary.