Question about 2005 Ford Focus

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My check engine light is still on after replacing both oxygen sensors and cleaning mass airflow.

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I would need to know the code you received but I'm assuming you're replacing these parts due to a lean concern. The focus is known for vacuum leaks at the pcv hose elbow. Look on the back side of the intake plenum between the engine and firewall and you'll see a vacuum hose/tube coming from the center of the intake going toward the drivers side of the engine. Check this hose, especially at the elbow for a sucked in or broken hose. If this isn't the problem, the easiest thing to do is to hook up a scan tool and monitor thr short term fuel trim pids. Spray the intake and surrounding area with 2+2 or a similiar accelerant. the fuel trims will go negative when you spray near the vacuum leak. Good luck. Be sure to clear the keep alive memory after the repair. This can be done with the scan tool or by disconnecting the negative battery terminal for 5 minutes. Good luck.

Posted on Apr 08, 2011


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Symptoms of faulty air flow sensor

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    Jul 09, 2016 | Cars & Trucks


    My Engine Check Light Is Illuminated

    There's nobody on Fixya who can give you a definitive answer as to why your engine check light is on. It just isn't possible, and nobody will tell you to replace parts because some of the parts can be pricey.

    If you can understand a number of the causes that lead to a check light coming on, it will go some way in helping you decide what may be the fault:

    The Oxygen Sensor
    Often referred to as a Lambda sensor.
    An oxygen sensor is fitted on the exhaust system before the catalytic converter. It monitors the unburned oxygen from the exhaust and detects how much fuel is being burned at any given time.
    A faulty oxygen sensor means it's not providing the right data to the computer and will cause a drop in miles per gallon. Some cars may have more than one oxygen sensor.

    Over time, the sensor becomes coated by burnt carbon waste from the exhaust and loses its ability to alter the oxygen / fuel mixture for different driving speeds and conditions. A faulty oxygen sensor also increases exhaust emissions.

    A failed oxygen sensor can eventually cause the catalytic converter to burn out. The smell of a burnt catalytic converter is likened to the smell of 'tom cat p**s'. A replacement catalytic converter doesn't come cheap.

    Mass Air Flow Sensor
    The mass airflow sensor tells the car's computer to add the correct amount of fuel based on the amount of air being drawn into the engine for combustion. A faulty mass air flow sensor also affects mpg, increases emissions, and can cause the car to stall.

    Mass airflow sensors can fail over time because of an improperly installed air filter - or an air filter that has never been changed. You should replace the air filter at least once a year to help prevent the airflow sensor from failing.

    Spark Plugs
    Yes, faulty spark plugs can cause the engine check light to come on - that's because misfiring plugs cause a problem elsewhere in the fuel/air management.
    You may feel a 'jolting' when accelerating. Spark plugs fail and there's not much you can do to prevent that from happening.

    Fuel Filler Cap
    Probably knows as the gas cap in the USA?
    Incredibly, an untightened or cracked filler cap can cause problems. Some modern cars even have an error code that suggests a faulty fuel cap.

    The Exhaust Gas Recirculation valve.
    In internal combustion engines, exhaust gas recirculation is a nitrogen oxide emissions reduction technique used in petrol/gasoline and diesel engines. An EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. It reroutes some of the exhaust gases which are emitted by the engine into the combustion chambers. This effectively reduces temperatures in the combustion chambers.
    The exhaust gases from the engine can cause the egr plunger (or 'butterfly valve' - which is a small circular disk inside the throttle body) to stick open or closed, leading to differing symptoms such as engine knock when fuel is ignited too early or rough running. It is the engine timing which is affected.

    Most EGRs can be removed and cleaned out. Most EGRs are expensive to replace.

    Camshaft and/or Crankshaft Sensor
    More often than not when these fail the engine will not start, but this isn't always the case nowadays. Some vehicles have a 'limp home' mode. Replacement of the faulty sensor is the only cure.

    There's other sensors too. Your car is a veritable network of data being transmitted from/to a whole host of interconnected sensors.

    For the home mechanic the most expensive - and frustrating - way of fixing something is to replace one part after the other in the hope that the problem is solved.

    Your first course of action should be to have a diagnostic test carried out. Identify the fault first. It's well worth paying a mobile mechanic to carry out a diagnostic test first.

    on Feb 08, 2016 | Cars & Trucks

    1 Answer

    Code 157

    Error code 157 on your vehicle indicates a problem with your mass airflow sensor. The mass airflow sensor gives a reading based on the air intake and output within the engine compartment. A properly functioning sensor will contribute to better fuel economy. In some instances, you may be able to clean your mass airflow sensor to clear the error code, but the error will most likely return in a short time. Fortunately, replacing the mass airflow sensor is a reasonably simple repair.

    Read more: How to Correct Engine Code 157 '

    Jan 17, 2013 | Ford Windstar Cars & Trucks

    1 Answer


    try cleaning the mass airflow sensor, and change the PCV valve. I would replace the PCV valve first cause that could cause it and its a cheap and easy fix, could be stuck and gunked up or clogged and barely any air is moving into the intake, if you clean the mass airflow sensor be careful not to touch the element and not to drop it handle with care it's expensive and is a fragile part, and use mass airflow spray cleaner only. Try that see if it fix's the problem if not I would check your vacuum lines particularity the ones going in and out of the intake from the pcv valve and the one going from the airbox to the engine, then check if any of the other small lines from your EGR are all connected and not cracked broke or damaged

    Feb 07, 2018 | Cars & Trucks

    1 Answer

    I recently had problems with my 2005 Mazda MPV stalling. I came to this great site and changed the IAC and it stopped stalling. But 2 days later my check engine light came on. The codes are P2197 P2195...

    The descriptions for your codes are:
    P2197 - H02S (RF) signal stuck lean
    P2195 - H02S (RF) signal stuck lean
    P2187 - Fuel System too lean at idle
    P0102 - MAF circuit low input

    Essentially what's happening is that your MPV is running too lean when at idle. Too much air and not enough fuel. As you speed up - it forces more air into the system which alleviates the problem.

    Examine your mass airflow sensor. It should be completely clean - no fuzzies on it at all. If so - purchase some mass airflow sensor cleaner to clean the sensor. ONLY USE THE PROPER CLEANER TO AVOID DAMAGING THE SENSOR. Disconnect the battery to reset the system and turn off check engine light.

    Otherwise you will need a scan tool to look at the voltages being supplied to/from the PCM for each of the Heated Oxygen Sensors and the Mass Airflow Sensor to determine which part is creating the problem.

    May 25, 2011 | 2005 Mazda MPV

    2 Answers

    The check engine light comes on and it dies on occasion. It is intermittent. Had it scanned and was told the only fault was mass air flow sensor. Cleaned the mass air flow sensor, replaced fuel filter and...

    Anytime you make a change to any part of the emissions system, its best to disconnect the
    battery for a few minutes. If you don't, the computer retains the fault code and it will usually keep
    coming back. When all power is lost to the computer, it will do a complete scan when reconnected
    and engine started. Try disconnecting the battery for a few minutes then reconnect and see what happens.

    Mar 05, 2011 | 1992 Buick Century

    2 Answers

    Sensor light is on and I had it checked at Advance Auto they said it was reading lean in bank 1 and 2. What does that mean and what do I do now?

    this can get very in depth to explain,but I will do may best. the oxygen sensor in the exhaust pipes are monitoring the amount of oxygen present in the exhaust stream, when all conditions are correct the oxygen sensors will fluctuate a voltage signal to the (power train control module)between one tenth of a volt to nine tenths of a volt, the higher voltage represents a rich condition and a lower voltage represents a lean condition. when the voltage sent from the oxygen to the module continues to only sent a lower voltage signal the module realizes that the engine is running lean,(not enough fuel) and then trips the check engine light on your dash. now a lean condition can be caused by many problems, first off the most common problem I see is that a person does not keep there air cleaner element clean with ends up contaminating the mass airflow sensor,which is in the air tube between the air cleaner housing and the engine this is a sensor with wiring leading into it,(sometimes its mounted right on the air cleaner within a aluminum housing)once removed which sometime requires a taper proof torx tip tool. you will see two small wires that almost look like miniature electrical heater elements ( like a small in house heater ) these little wires get very dirty when the air filter element is not changed properly,they should be light silver if they are black or show signs of dirt,they can be cleaned using a mass airflow meter cleaner which can be obtained at a good parts not touch these wires as they are very fragile,the only approved way to clean these are to spray them with a approved mass airflow cleaner and I have taken a tooth brush and very carefully brushed the dirt and grime off them. this sensor monitors the amount off air flow coming into the engine and if the wires on this sensor are dirty,the sensor cannot accuratly monitor the air flow which will make your engine run very lean.if you do not see any signs of dirt or bulid up on this sensor, you should look for hoses that are disconnected or cracked that could cause a vacuum leak,and repair as needed. also low fuel presure would cause a lean condition. if you don"t find a consern with the mass airflow sensor and no hoses cracked or unhooked the other thing you can try is to get a can of brake cleaner (must be flammable)from a parts store and use the straw that came with the brake cleaner and very carefully spray it around under the hood at the top of the motor near the intake manifold, if you hear the engine speed increase you have found your vacuum.leak and repair as needed

    Dec 29, 2010 | 1999 Mercury Cougar

    1 Answer

    When engine light stay on

    there are several things that can cause this. it could be the egr valve,or mass airflow sensor , or oxygen sensor , or throttle position sensor . Disconnect the negative battery cable for a minute , then reconnect start the car the engine light should be off , but if it comes back on start checking the above items.

    Oct 27, 2010 | 1996 Nissan Sentra

    3 Answers

    Own a 1996 Grand AM GT 2.4 quad 4..manual...engine idles rough, and bucks when accellates or between shift of gears. Have replaced the coil packs, plugs, and spark tower( you may call different name) also...

    This could also be a clogged fuel filter or a stopped up mass airflow sensor. remove and replace the fuel filter and clean the mass airflow sensor with carburetor cleaner then reinstall the breather assembly, this should take care of the problem. If this doesn't you may have to run a scan and see if there are any trouble codes stored in the computer to find out what the problem is. Hope this helps, good luck!

    Sep 02, 2009 | 1996 Pontiac Grand Am

    1 Answer

    Isuzu hombre check engine light

    after you did that did you hook it to a car computer to reset the lite? most need this and you can go to a auto zone and rent the computer for free just a deposit and then you get that back. the computer will do it almost for you.

    Oct 27, 2008 | 1997 Isuzu Hombre

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