P0172

The scan tool indicates Diagnostic Trouble Code (DTC) P0172: The fuel system is too rich.

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

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

P0106-8, P1128*3*5, P1129*3*5: MAP Sensor
P0135: Primary HO2S Heater
P0137, P0138: Secondary HO2S
P0141: Secondary HO2S Heater
P0401: EGR Flow Insufficient*1
P0441: EVAP System Insufficient Purge Flow*6
P1259: VTEC System*2
P1491: EGR Valve Lift Insufficient*1
P1498: EGR Valve Lift Sensor High Voltage*1

*1: D16Y5 engines
*2: D16Y5, D16Y8, B16A2 engine
*3: '97 models
*4: '96 models
*5: '98 - 00 models
*6: '96 D16Y5 engine, '96 D16Y7 engine, '96 D16Y8 engine (sedan), '97 D16Y5 engine, '97 D16Y7 engine (coupe: KA, KC models, sedan KA, KC, KL (DX) models, hatchback: all models), '97 D16Y8 engine (sedan: '(A, KC models)

Possible Cause

- 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 range/performance*4
- EGR System insufficient flow*1
- EVAP Purge Control Solenoid Valve leaking, stuck opened Valve Clearance




Troubleshooting Flowchart