Diagnostic Aids

Check for any of the following conditions:

• Check for a restriction in the inlet air passage. A duct or inlet hose that collapses when hot or that is blocked by debris can cause a DTC P0172 to set.
• Check for the correct fuel pressure. The fuel system will be rich if the fuel pressure is too high. In order to determine the cause of a DTC P0172 monitoring the fuel pressure while driving the vehicle at various road speeds may be necessary. Refer to Fuel System Diagnosis .
• Check for fuel contamination of the crankcase. Fuel that has entered the crankcase can release vapors that enter the engine through the positive crankcase ventilation (PCV) system, thereby causing a rich running condition.
• Check for a damaged wiring harness. If the harness appears to be OK, observe the HO2S 1 display on the scan tool while moving the connectors and the 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 exhaust oxygen content readings. If contamination is found, determine the cause 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 voltage in the HO2S signal circuit causing a false rich indication.
• Check the HO2S 1 and the mass air flow (MAF) sensor for a faulty electrical connection 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 in Wiring Systems.

If a DTC P0172 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.