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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
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How to repair codes 171&174 2002 Toyota Avalon 3.0v6

Customer Question

how to repair codes 171&174 2002 Toyota Avalon 3.0v6
Submitted: 2 years ago.
Category: Toyota
Expert:  Toyota Service replied 2 years ago.

Hello. Welcome to Just Answer. Please allow me to assist you. These are the criteria that will set a P0171/174:

 Air induction system
 Injector blockage
 Mass air flow meter
 Engine coolant temp. sensor
 Fuel pressure
 Gas leakage on exhaust system
 Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
 A/F sensor (bank 1, 2 sensor 1)
 PCV hose connection
ECM

More often than not, all that is really needed is a good cleaning of the Mass air flow Sensor. Locate the unit in the tube between the engine and the air filter box. Disconnect the wire connector. Remove the sensor form the tube. Using spray brake cleaner (available at auto parts stores), liberally spray the interior of the sensor and let it AIR DRY. Do NOT use compressed air to speed up the drying process, you will damage the sensor. After it dries, fit the sensor back into the tube, reconnect it and drive the car. If the interior of the sensor was dirty, the engine control unit will read new values form the sensor and the light should go out.

Expert:  Toyota Service replied 2 years ago.

Hello. Welcome to Just Answer. Please allow me to assist you

Expert:  Toyota Service replied 2 years ago.

The following is the criteria for setting the P0171/P0174 codes:

 Air induction system
 Injector blockage
 Mass air flow meter
 Engine coolant temp. sensor
 Fuel pressure
 Gas leakage on exhaust system
 Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
 A/F sensor (bank 1, 2 sensor 1)
 PCV hose connection
ECM

Expert:  Toyota Service replied 2 years ago.

The P0171/P0174 codes are usually caused by a dirty Mass Air Flow Sensor. The 171/174 indicates that the system is being read by the sensor as 'too lean'.

Expert:  Toyota Service replied 2 years ago.

The recommended procedure would be to locate the sensor in the tube between the engine and the air filter. Remove the wire connector and extract the sensor after removing the retainer screws or bolts. With spray brake cleaner, liberally spray the interior of the sensor and let it AIR DRY. Using compressed air will damage the sensor. After it has dried, refit the sensor and reconnect the wire connector. If the senor was dirty inside, the light should go out after 5 miles or so of driving.

Expert:  Toyota Service replied 2 years ago.

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