DTC P0171: Fuel System Too 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: 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* *: D17A9 engine Check the fuel pressure, refer to the '01 Civic Shop Manual on this CD (see page 11-131). Is fuel pressure OK? YES - Go to step 2. NO - Check these items: If the pressure is too high, replace the fuel pressure regulator, refer to the '01 Civic Shop Manual on this CD (see page 11-138). If the pressure is too low, check the fuel pump, the fuel feed pipe, the fuel filter and replace the fuel pressure regulator, refer to the '01 Civic Shop Manual on this CD (see page 11-138). 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. Does it stay at less than 0.3 V or more than 0.6 V? YES - Replace the primary HO2S (Sensor 1). NO - Go to step 4. Turn the ignition switch OFF.

With a vacuum pump (A), apply vacuum to the evaporative emission (EVAP) canister purge valve (B) from the intake manifold side. Does it hold vacuum? YES - Go to step 6. NO - Replace the EVAP canister purge valve. Turn the ignition switch ON (II). Check the manifold pressure with the scan tool. Does it indicate atmospheric pressure? YES - Go to step 8. NO - Replace the MAP sensor. Start the engine. Check the MAP with the scan tool. Is a MAP of 40.0 kPa (300 mmHg, 12.0 in.Hg) or less indicated within 1 second after starting the engine? YES - Check the valve clearances and adjust if necessary. If the valve clearances are OK, replace the injectors. NO - Replace the MAP sensor.