P0171 and P0174 Codes – Don’t change an Oxygen Sensor Before Reading This

So your car’s CEL (always check Engine Light) is on and also you had the codes scanned at a local parts shop. (Or maybe used your own OBD scanner to extract the car faults). Your car or truck has either a P0171, P0174 lean fault code or both stored in the pc, these codes derive from Oxygen Sensor (O-2) readings.

A lean code or codes suggest that there surely is too-much air in the exhaust.

Bear in mind parts shops have staff members having good motives nonetheless they may not have the experience necessary to understand what the problem codes actually imply. These codes derive from air dimensions in the exhaust. A typical blunder with lean codes should change the air detectors.

This may be a very pricey blunder that will maybe not mend the problem. Particularly if both codes are present, considering that the possibility of both O-2 detectors a failure at the same time is extremely not likely.

Likely the main cause is vacuum pressure drip. A vacuum cleaner drip may be caused from vacuum pressure hose, intake gasket and maybe even a leak in the air consumption hose from MAF (Mass Air Flow Sensor).

Pay attention for a hissing noise that could lead you to the origin regarding the issue. Some professionals uses a propane bottle with a hose accessory to assist pinpoint vacuum cleaner leaks.

With today’s computers it is not rather as simple to check on for vacuum cleaner leaks that way considering that the ECU (Electronic Control product) will make up quickly for the included gas and a modification of idle is harder to note.

Oxygen sensor readings may be administered with a scan device while checking for leaks with propane, by shopping for increased readings when enriching the blend. One other way professionals can look for vacuum cleaner leaks is by using a smoke test.

By introducing smoke into vacuum pressure hose on engine, the drip will be uncovered as soon as the smoke escapes from issue area.

Aftermarket air filters that use oil on factor can occasionally damage the MAF. Over oiling air filter may allow some excess to obtain on MAF sensor cable or factor. This might alter the reading, fooling the ECU into witnessing just about air flow therefore changing the air/fuel blend wrongly.

We as soon as worked on a car or truck that could maybe not begin which had an issue with a MAF. When looking at the cable in the MAF, there was a burned bit of rubbish that caused it to be’s method at night air conditioner filter. After washing the sensor the car ran completely.

The ash that has been on MAF sensor cable ended up being altering the reading by enriching the blend plenty that car cannot operate. After talking with the buyer, he said air filter ended up being simply altered. This was clearly when some rubbish got into the air intake hose that decided on hot wire regarding the MAF.

Fuel Pressure could also cause a lean condition. If gas filter is blocked or perhaps the gas pump pressure is reasonable, there might be higher degree of oxygen in the exhaust also. In most cases though, the ECU will make up for the paid down gas amount. So this is one of the least likely factors that cause a lean code.

Eitherway, if want to get technical data from ECU about this code and many others, just plug a scantool to car and you’ll see all the faults reported..

P0171 and P0174 Codes – Don’t change an Oxygen Sensor Before Reading This
4.1 (82.86%) 21 votes

9 Responses to P0171 and P0174 Codes – Don’t change an Oxygen Sensor Before Reading This

  1. P0171 suggested causes:

    Ignition misfiring
    Intake air leaks
    Lack of fuel Faulty
    Mass Air Flow (MAF) sensor
    Incorrect Positive
    Exhaust gas leaks
    Crankcase Ventilation (PCV) hose connection
    Faulty front heated oxygen sensor
    Incorrect fuel pressure
    Faulty fuel injectors

  2. 01 Toyota Avalon w/ PO171 & PO174. Noticed codes appeared after transmission fluid change about a week ago. Any correlation? Just Coincidence?

  3. The catalytic converter is a very important part of the emissions control
    system on your vehicle. (Chapter 7 tells you what this part looks like and
    how it works.)

    It’s usually good for the life of a vehicle, but occasionally it
    does fail. The best thing you can do is be alert for signs of trouble and head
    for a service facility if you suspect that the catalytic converter is malfunctioning.

    Technicians will put your vehicle on an electronic diagnostic machine to
    locate the source of the problem, possibly remove the oxygen sensor from
    the exhaust manifold or exhaust pipe ahead of the catalytic converter to see
    if that changes things, and replace the catalytic converter, if necessary.

  4. With my 2006 Trailblazer I6 I had had the P0171 code on and off for awhile, but it eventually became a permanent thing. Both the method of spraying carb cleaner around and the use of a smoke machine indicated that the intake manifold was leaking. I decided to just tighten the bolts and see if that would solve the problem instead of replacing the manifold gasket. There are ten bolts and the ones closest to the front of the engine were not loose, but as I moved further back the bolts became progressively looser. Towards the middle of the manifold the bolts were definitely loose requiring perhaps a quarter turn to tighten them, the ones toward the rear took perhaps a full turn, and the very last one probably two full turns.

    I used a variety of 1/4″ drive tools to get the job done., including a variety of extensions including wobbler extensions, universal joint, and regular and 10mm deep socket.

    I did unbolt the ECU to improve access, as well as removing the large vacuum hose going to the brake booster. The front ones would be much easier if the alternator was removed, but I left it on. I also disconnected the battery because toward the rear of the engine the hot terminal of the starter is fairly close to where you will be working with your sockets.

    Each bolt posed its own particular challenges. I suggest you do not do this when you are pressed for time.

    The problem is solved!

  5. I have a 97 ford f150 getting p0174 I’m getting perfect air vacuum and perfect fuel pressure values after testing both.

  6. I should be more clear: I feel like I’ve tried everything…can’t find the fault, still getting the p0174 code.

Leave a reply

About Us

Total Car Diagnostics helps fellow home car owners, mechanics, technicians, garage shops, engineers, ECU programmers and auto repair centers — to significantly cut down on maintenance, repair costs, time, money, energy… and all other frustrating headaches involved with dealing with vehicles — by providing cost-effective advice, tools and recommendations.


facebook Total Car Diagnostics  LinkedIn Total Car Diagnostics  YouTube Total Car Diagnostics

Home | About Us | Contact | Terms of Service | Privacy Policy | Tuning Disclaimer | Affiliate Program | Shop

Address: PO Box 1315, Byron Bay, NSW, 2481, Australia. Support phone: (+61) 401 605 241

© Copyright 2021 by Total Car Diagnostics. All Rights Reserved.