P0172

(_PO172_)
- The scan tool indicates Diagnostic Trouble Code ((DTC) P0172: The fuel system is too rich [Rear Bank. (Bank 1)]

Description
By monitoring the Long Term Fuel Trim, long term malfunctions in the fuel system will be detected.
If a malfunction has been detected in two consecutive trips, the MIL will come on and DTC P0171, P0172, PO174 and/or P0175 will be stored.

NOTE:
- If some of the DTCs listed below are stored at the same time as DTC P0171, P0172, P0174 and/or P0175, troubleshoot those DTCs first, then troubleshoot DTC P0171, P0172, P0174 and/or P0175.

PO1O6-8: MAP Sensor
P0135: Rear Primary HO2S Heater (Bank 1, Sensor 1)
P0137-8: Rear Secondary HO2S (Bank 1, Sensor 2)
P0141: Rear Secondary HO2S Heater (Bank 1, Sensor 2)
P0155: Front Primary HO2S Heater (Bank 2, Sensor 1)
P0157-8: Front Secondary HO2S (Bank 2, Sensor 2)
P0161: Front Secondary HO2S Heater (Bank 2, Sensor 2)
PO4O1: EGR Flow Insufficient
PO441: EVAP System Incorrect Purge Flow
P1259, P1279: VTEC System
P1491: EGR Valve Lift Insufficient
P1498: EGR Valve Lift Sensor High Voltage

Possible Cause
(System too rich)
- Fuel Pressure Regulator clogged, stuck closed
- Fuel Return Pipe clogged
- Fuel Injector leaking
- Gasoline doesn't meet Owner's Manual spec.
- Primary HO2S (Sensor 1) deteriorated
- MAP Sensor wrong characteristics
- EGR System malfunction (too much flow)
- EVAP Purge Control Solenoid Valve leaking stuck opened Valve Clearance too loose