DTC P0171: Fuel System Tool Lean; DTC P0172: Fuel System Too Rich

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 P0171 and/or P0172.

P0107, P0108, P1128, P1129: Manifold Absolute Pressure (MAP) sensor

P0135: Primary Heated Oxygen Sensor (primary HO2S) (Sensor 1) heater

P0137, P0138: Secondary HO2S (Sensor 2)

P0141: Secondary HO2S (Sensor 2) heater

P0401, P1491, P1498: Exhaust Gas Recirculation (EGR) system

P1259: VTEC system

Special Tools Required Vacuum Pump/Gauge, 0-30 in Hg. A973X-041-XXXXX

Check the fuel pressure (see FUEL PRESSURE TEST ).
Is the fuel pressure OK?
1. YES -Go to step 2.
2. NO -Check these items:
- If the pressure is too high, check the fuel pressure regulator and the fuel return pipe.
- If the pressure is too low, check the fuel pump, the fuel feed pipe, the fuel filter, and the fuel pressure regulator.
Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.
Check the primary HO2S (Sensor 1) output with the scan tool or the HDS.
Does it stay at less than 0.3 V or more than 0.6 V?
1. YES -Replace the primary HO2S (Sensor 1).
2. NO -Go to step 4.
Turn the ignition switch OFF.
Install a vacuum pump to the evaporative emission (EVAP) canister purge valve (A) on the EVAP canister side.

Fig 1: Installing A Vacuum Pump To The Evaporative Emission Canister Purge Valve On The EVAP Canister Side
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Disconnect the EVAP canister purge valve 2P connector.
Start the engine.
Is there vacuum on the gauge?
1. YES -Check the valve clearances and adjust if necessary. If the valve clearances are OK, replace the injectors.
2. NO -Replace the EVAP canister purge valve.