Diagnostic Aids

Check for any of the following conditions:

• Check for vacuum leaks.
• Check for exhaust leaks.
• Check for the correct fuel pressure. The fuel system will be lean if fuel pressure is too low. In order to determine the cause of DTC P0171 monitoring the fuel pressure while driving the vehicle at various road speeds may be necessary. Refer to Fuel System Diagnosis .
• Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 1 display on the scan tool while moving the connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.
• Check for a contaminated oxygen sensor. Silicone and other contaminants can cause the oxygen sensor to provide false lean exhaust readings. If contamination is found, determine the cause of the contamination and correct the condition before replacing the HO2S.
• Inspect the HO2S 1 for water intrusion into the wiring harness and the sensor housing. Water can create a short to ground in the HO2S signal circuit, causing a false lean indication.
• Check the HO2S 1 and the mass air flow (MAF) sensor for faulty electrical connections to the PCM.

An intermittent malfunction may be caused by a fault in the HO2S 1 electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs .

If DTC P0171 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.