Diagnostic Aids

• The scan tool output control feature, Fuel Injector Modification, can be used at idle to check the oxygen sensor performance. Commanding the Fuel Injector Modification Commanded State to 25 percent should cause the HO2S 1 voltage to decrease to less than 3V. Changing the Fuel Injector Modification Commanded State to -12 percent should cause the HO2S 1 voltage to increase to more than 3.35V. An oxygen sensor that fails to respond accordingly may be faulty or contaminated. When performing the Fuel Injector Modification with the scan tool, the Loop Status will remain Open Loop and the Short Term FT will be fixed at 0 percent.
• Inspect for a contaminated HO2S. Silicon contamination of the HO2S can cause a low signal voltage to be indicated. Silicon contamination is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. Before replacing the HO2S determine the cause of the contamination and correct the condition.
• Verify the PCM to engine electrical grounds are OK.
• An incorrect fuel pressure-The fuel system can go rich if the fuel pressure is too high and DTC P2196 may be set. Refer to Fuel System Diagnosis .
• Fuel contamination-Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
• An incorrectly calibrated fuel injector. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and Fuel Injector Balance Test with Special Tool .
• Inspect for correct operation of the crankcase ventilation system.
• An evaporative emission (EVAP) system condition-A saturated EVAP canister or faulty operation of the EVAP canister purge solenoid can set a DTC P2196. Refer to Evaporative Emission Control System Diagnosis .
• An intermittent malfunction may be caused by fault in the HO2S 1 electrical circuit. Inspect the wiring harness and components for any intermittent conditions. Refer to Intermittent Conditions .

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.