Question about Mitsubishi Montero

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  • P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2) This has to do with the "pre cat" on the B or #2 side of the exhaust. What this means is that the chemical make up inside the catalyst becomes slow to respond and even though the O2 sensors are doing there job, they can not over compensate for the cat failing. It should be attatched to the exhaust manifold just prior to the cat in the exhaust where the 2 sides come together. You basically have 3 catalytic converters.
  • Posted on May 18, 2011


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    Check engine light on, scan code p0175. I already change MAF and check O2 sensors. have you any advice?

    code p 0175 refers to system too rich bank 2===causes --intake blocked ---EVAP canister purge valve ---fuel pressure ---EGR system---injector/s ---HO2S
    basically you changed the wrong sensor as the HO2S sensor is the sensor in the exhaust manifold or before the cat converter
    It tells the ECM to adjust the injector flow for that bank to a leaner mixture (O2 sensors are after the cat and tell the ECM if the mixture is right for complete burn
    it could be from a bad injector that is leaking at the tip and the ECM cannot control the fuel mix

    Jan 21, 2016 | 2006 Hyundai Tucson 4WD 2.7L V6

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    Here's a link to the issues associated with a P0174 code:

    There's a bit of a punch list of stuff that could be causing this code. If you have never changed the O2 sensors on this car that is where I would start; replace all of them. Get OEM exact replacements versus "universal" fit O2 sensors.
    The Mass Airflow Sensor (MAF) may be dirty. There is specially formulated cleaner for removing any built up mung on the sensor.
    The PCV system can be checked for proper flow. Replace the PCV and/or clean the system if there is no valve.
    Bring the car in and have the injectors professionally cleaned.

    You're probably in the neighborhood of 165-170K. If you've never done any preventive or regular maintenance then there could be a lot of issues with your car. The P0174 is a lean condition. It could be bogus inputs to the engine management computer (via bad O2 sensors and/or a dirty or bogus MAF sensor). It could be really dirty injectors because they've never been cleaned and if you've been filling up with non-top tier fuel (because you're saving 2 cents a gallon) then it's a sure bet the injectors are dirty. Running lean comes from air leaks into the manifold post MAF sensor. This could be from rotted vacuum hoses or cracked/broken vacuum fittings. There's just too many possibilities to be able to nail it down for sure. Use the link and the info there to start your trouble shooting.

    Apr 13, 2014 | Mitsubishi Montero Sport Cars & Trucks

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    Rough idle and smells like gas when driven

    When checking for Vacuum leaks, did you use a water spray bottle on seams and vacuum lines and EGR pod?(engine running)

    Check for air leaks in exhaust before O2 sensors. O2 thinks its running lean from air leak in exhaust header and enrichens fuel charge.

    Fuel injectors dirty, not closing tight. Switch injectors to other bank and see if Error Code moves to relocated injectors.

    Bad spark plugs, check if you have fuel runners in your intake.

    Jan 05, 2014 | 1998 Volkswagen Jetta

    1 Answer


    Well code 431 means the computer does not think the catalytic converter is working correctly. The engine computer uses data from the O2 sensors to monitor the cat.
    The actual problem could be the cat, one of the O2 sensors, a fuel problem, or other things. The O2 sensors would need to be watched with a scanner to find the issue.

    Jul 17, 2013 | 2002 Mitsubishi Diamante

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    2003 jaguar s type r 4.2ltr. check engine light still on after replacing o2 sensors for code po172.can anyone help?

    Don't think the sensors were the problem

    You never change the rear monitors anyway

    You use the code & reference material, to diagnose
    what the code tells you,doubt that was done

    Look at fuel trim on that bank, it should be rich

    Check & clean MAF Sensor & all intake ducting for vacuum leaks
    Smoke test intake & manifold, as well as exhaust before cat if you need to

    If fuel pressure is good & only one bank is rich scope O2 Sensor
    to confirm then scope the injectors on that bank & you will se if they stick

    May have to remove all injectors & mail away for ultra sonic cleaning

    Feb 17, 2013 | Jaguar S-Type Cars & Trucks

    2 Answers

    After testing the MAF sensor, changing the PCV & CO sensors, I still get the check engine light, 1999 ford explorer sport 4.0 SOHC 6 cyl I've read to check the intake manifold and then go fu

    What is a CO sensor? Never heard of it. a 1999 OBD2 ford has approximately 1600 possible fault codes most of which can turn on the light. If you dont know which one is turning it on, you are guessing randomly which is expensive and usually unsuccessful. get the code(s) and then diagnose the possible causes. The vehicle you list (99 4L explorer) rarely had injector problems. Much more common were EGR sensor(DPFE) sticking at voltage, evap problems, misfires, and lean conditions due to dirty MAF, or vacuum leaks. get the fault code, or you will not fix the problem.

    Dec 29, 2012 | 2007 Toyota Land Cruiser

    2 Answers

    Code p0170

    What year vehicle ? mass air flow or speed density fuel control . Do you have a scan tool that can view sensor data . What are the fuel trims ( short & long term ) showing ? PCM problem ? O2 sensors stuck lean , adding propane , do the O2 sensors go rich ?

    Jan 10, 2018 | Chrysler Town & Country Cars & Trucks

    3 Answers

    2004 Ford F150 5.4l XLT 4x4. P0174 - Can't resolve! :(

    Short of actually getting my hands on your truck to do the diagnosis myself... These are the things I can think of off-hand that would cause your P0174 and not necessarily set other DTCs.

    - A faulty upstream Bank 2 O2 sensor or wiring (though you already have this base somewhat covered and Ford O2 sensors are tough, usually don't see failure except in cases of contaminated fuel or excessive use of over-the-counter fuel additives)

    - A bent, disconnected, or broken Intake Manifold Runner Control rod or butterfly assy on Bank 2

    - An exhaust leak on Bank 2 (esp. since you mentioned headers)

    - An intake manifold leak either at the gasket or injector o-rings on Bank 2

    - A weak or partially stopped-up injector(s) on Bank 2. Though I find this unlikely since you mentioned there was no misfire.

    - A plugged or restricted Catalyst on Bank 2. Also seems unlikely given that you do not experience misfire or low power concerns.

    - A faulty Powertrain Control Module. This option, though not unheard of, is VERY unlikely in my experience with these trucks.

    If I think of anything else I will let you know. I wish that I could help more, remote diagnostics without all the needed tests and information on a problem such as this amounts to little more than conjecture.

    Feb 04, 2010 | 2004 Ford F150

    2 Answers

    1999 ford E150 starts and runs fine, after warm up at idle, rpms varry. will stall at stops but starts and runs fine at high idle and on highway. Trouble codes are 02s bank 1 and bank 2, both lean. also...

    I had same problems w/ my 99 Chateau 5.4L. EGR-Ensure port into intake and pipe from exhaust are clear using low pressure compressed air. Pull vacuum on EGR diaphram and ensure it opens and closes smoothly. If this checks out then problem is probably in the EGR sensor (mine had both ports and hoses clogged w/ aluminum corrosion from the sensor, cleaned out hoses and lines to exhaust pipe w/ compressed air, ended up having to change the sensor). IDLE AND O2 SENSOR- Caused by vacuum leaks in the PCV line (line is plastic wrapped w/foam insulation; was cracked under the insulation; both rubber end connectors at manifold and pcv valve were softened, collapsed and leaking; allowing excess air into the manifold after the mass air flow sensor which throws off the O2 sensors. engine computer does not read O2 sensors until after engine is warmed up which is why idle is fine until then).

    Sep 23, 2009 | 1999 Ford Econoline

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    Engine light was on and engine idles rough.

    these O2 sensors are cat convertor check sensors. id be checking cat convertors and hopefully you should try replacing if not all ready is the front bank 2, O2 sensor
    if you have scanner can you see fuel trims in data display to confirm high fuel trim only on bank 2 either +-5 or more indicates problem and if bank 2 sensor 2 has fixed high 700mv reading cat no good(warm idling)

    Jul 10, 2009 | 1998 Isuzu Rodeo

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