Can changing air fuel sensor causes damage to fuel pump

Tiny
JESSE R. VALLANDINGHAM
  • MEMBER
  • 2010 TOYOTA RAV4
  • 2.5L
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 32,000 MILES
PO171 system lean code, CEL, 4wd and Slippery road conditions lights are on. Changed bank 1 air/fuel sensor. Can changing this sensor damage the fuel pump or was the fuel pump the problem to begin with?
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Friday, June 23rd, 2017 AT 8:06 AM

11 Replies

Tiny
CARADIODOC
  • EXPERT
Those two parts have nothing to do with each other. There is no way to know if the fuel pump caused some problem. You did not say what the symptom or problem was that the pump solved.

Code 171 refers to a lean condition. That is reported by a properly-working oxygen sensor. Changing the sensor is not going to solve the results of the problem it was seeing. The most common causes of code 171 are a vacuum leak, or a spark-related misfire that sends unburned air and fuel into the exhaust system. It is the unburned oxygen that gets detected as the lean condition, but you would smell unburned fuel at the tail pipe for that problem.
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Friday, June 23rd, 2017 AT 2:48 PM
Tiny
JESSE R. VALLANDINGHAM
  • MEMBER
My car is a 2010 Rav 4 2.54cyl. Base model 4WD. Symptoms. CEL, 4WD and slippery road lights on the dash. Car runs normally but hesitates on acceleration and some gear changes. To date the car has had all the coils and spark plugs changed, new fuel pump and air/fuel sensor. I have visually inspected vacuum lines. New air filter as well and mass airflow meter is clean. Remaining options include intake manifold gasket or the o2 sensor.
Have recently been told that the intake valves could also do this bit I very seriously doubt it.
The mileage reads 32,000 miles but this is in question as I live in Nigeria and it is very likely the instrument cluster has been hacked.
On a personal note I do not think the garage where I have been servicing this car is capable of solving this problem. They can only replace parts. Not much else.
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Saturday, June 24th, 2017 AT 5:03 AM
Tiny
STEVE W.
  • EXPERT
You really need to find out what codes are turning on the CEL. 4WD and traction control suggest it could be speed sensor or ABS related but likely not engine related. The dash could be causing problems if it was not programmed correctly to match the vehicle. Multiple modules talk through the dash to other modules, if something is wrong on the data bus you can get all kinds of strange symptoms.
There are multiple scan tools you can get very reasonable. The TOPDON Elite is not a bad tool if you can get one shipped to you.
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Saturday, June 24th, 2017 AT 3:58 PM
Tiny
JESSE R. VALLANDINGHAM
  • MEMBER
Scan tool reads PO171, lean bank 1. But as I have stated I have already changed the A/F sensor in bank 1. The parts replacement garage is suggesting intake valves may be bent. Personally I think he is bent.
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Sunday, June 25th, 2017 AT 2:51 AM
Tiny
CARADIODOC
  • EXPERT
What you are calling the air/fuel sensor is the oxygen sensor. They only measure oxygen, not fuel. Your terminology can confuse someone who is thinking about the mass air flow sensor, which actually does not measure fuel either. Many people call that the "air/fuel" sensor because its readings are used to calculate the amount of fuel the engine needs.

What is important to understand is the oxygen sensor is reporting a lean condition. That is what it is supposed to detect when the condition exists, and that can only be done by a properly-working sensor. Replacing the sensor is not going to solve the condition it is detecting.

The way to approach this is to connect a scanner and view live data, then see what you can do to affect the oxygen sensor's readings. You will see it switching between "rich" and "lean" about two times per second once the engine is warmed up. To set code 171, you will typically find it staying "lean" longer than normal, but it is also possible for the lean condition to only occur at certain times, like extended highway driving. For that, most scanners have a "record" feature that allows you to record a few seconds of sensor data when the problem occurs. In this case you would press the "record" button when the check engine light turned on. That would be when the problem occurred and was detected. Later you can plat it back slowly and see what changed that may have triggered the problem.

If you see an excessively-lean condition with the engine idling, you can pinch off various vacuum hoses, then observe if the oxygen sensor reports longer "rich" pulses. The scanner will also show the voltage being developed by the O2 sensor but those bounce around a lot, so it is hard to tell if pinching a vacuum hose caused a change. You can also spray some water over the engine while it is idling and still cool. If you see it get sucked in, typically through an intake manifold gasket or vacuum hose, you found the leak.

As a last resort, you can use a smoke machine to inject a white, non-toxic smoke at two pounds of pressure into a vacuum hose, then watch where it sneaks out. That can identify leak locations that are not easy to see otherwise.

Also be aware that almost all vehicles other than Chrysler products use the mass air flow sensor you mentioned. The fresh air tube between it and the throttle body can not have any leaks from loose hose clamps or cracks. Any air that gets into the engine without going through that sensor will not be measured, and no fuel will be calculated to go with it. That will result in a lean condition.
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Sunday, June 25th, 2017 AT 2:03 PM
Tiny
STEVE W.
  • EXPERT
JESSE
You say you have the CEL light on PLUS the "4WD and slippery road lights" are on. The P0171 is ONLY an engine control code. That is a completely different controller than the 4WD and slippery road" (Traction control) systems. Your scan tool probably cannot access those systems to read the codes they have stored, that is very common unless you have a top of the line scan tool. But there will be other codes in the ABS and transmission controller giving reasons why those lights are on.

As for the P0171, as DOC says that code actually shows that the sensor is working and is NOT the problem. The problem is a lean condition. It could be caused by a vacuum leak, a fuel pressure issue or even a minor exhaust manifold leak that lets in a tiny amount of air before the sensor.

The first one is the most common, a vacuum leak will cause a lean condition because it is considered "unmetered air" basically air that the computer doesn't know about. Because it doesn't know the extra air is in the engine it doesn't add extra fuel, and you get a lean condition.

Low fuel pressure can cause a lean condition because the injectors are basically nothing more than a valve that is turned on/off by the computer. The computer thinks you have between 45 and 50 PSI of fuel pressure, it doesn't actually measure the pressure. The injectors are designed to flow a set amount of fuel for a set time period based on that pressure. The "normal" fuel pressure is designed to provide fuel all the way up to maximum RPM. Now say you have a clogged fuel filter or weak fuel pump. The computer doesn't see those, it says I need to let in 100 parts of fuel based on the amount of air I see. It opens the injector for the correct amount of time, BUT because of the low fuel pressure only 90 parts of fuel actually are delivered. This will show up as a lean condition, the ECM will try to correct it by increasing the amount of fuel, but the lower pressure won't allow enough fuel to flow to correct the problem. The computer then decides "Well I can't fix it, turn on the light and tell them I'm running lean" You get the P0171 code.
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Sunday, June 25th, 2017 AT 5:03 PM
Tiny
JESSE R. VALLANDINGHAM
  • MEMBER
Thank you Steve W. And CARADIODOC for your replies. You have been very helpful in aiding me. I have a very good idea of where to look next.

To CARADIODOC: I know everyone calls them Oxygen Sensors and most vehicles have at least 2 these days and when you go to replace these parts, one is typically more expensive than the other. In my case, the Bank 1 sensor is located in the exhaust manifold. I only called it an Air Fuel sensor because that is what Toyota calls it and its how they mark the box in comes in. The other sensor is located after the catalytic convertor and for sure its called an oxygen sensor.

Its all a bit confusing O2 sensors, Mass Airflow and fuel pressure. Because of this I know my garage can not handle this job and I will have to take it to a Toyota Service center here in Abuja and just hope for the best and pay a fortune.

Once again, Thank you both. I feel much better talking to people who understand and who know how to remove a fuel pump without cutting a hole in the floor.

TOP TIP when living in Africa. If you need your car serviced for any reason, NEVER TAKE YOUR EYES OFF OF IT. If you leave your car with a garage, they will take good parts off your car and replace them with the bad parts from another customer. As mentioned they will cut holes in your floor rather than dropping the tank. You stand over your car the whole time. Even if you do not know anything about cars.

Thanks again.
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Monday, June 26th, 2017 AT 4:21 AM
Tiny
STEVE W.
  • EXPERT
MAF - This sensor measures the air going through it. There are a couple types used. The most common is a hot wire. Basically the computer sends current through a special resistor and measures the temperature. Air going over the wire tries to cool it, the ECM measures how much current it takes to keep it heated and that number tells it how much air is passing through the sensor. The next is a vane type, these are simply a door that the air pushes open. The farther it opens the more air is entering the intake.

Oxygen / O2 sensors - these use a couple of materials to determine the oxygen content of the exhaust gases. Early vehicles used one sensor, modern vehicles usually have one in the exhaust manifold, another behind the converter, some have a third behind a second converter as well. So you could have 6 sensors or more on a multiple bank engine.
These also come in two types. One is a wide band type which is commonly called an Air/Fuel ratio sensor. (Which is the type your car has) and the more common narrow band that is the rear sensor (post cat) on your car. They work on the same principle but cover different ranges of fuel mix. That allows the computer to have better control of the engine. They are not interchangeable.

Fuel pressure - This can get interesting. There are a couple types of pressure control used these days. The "simple" type uses a pump that gets full battery voltage all the time and has a spring type pressure regulator in the line to keep the pressure at the desired level. (Your car has this type). The other system uses a pressure sensor on the fuel rail to tell the computer the actual fuel pressure. The computer then tells a fuel pump driver module to increase or decrease the pressure based on the programming table in the computer. The driver module uses pulse width modulation to turn the pump on/off very fast. The more on time the higher the fuel pressure. Most pumps produce much more pressure than needed so some type of regulation is needed. (Yours for instance can produce close to 70 PSI)

That isn't something limited to Africa, there are dishonest shops all over the world. They are one of the reasons this site exists. To help folks who don't have a shop they really trust.
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Monday, June 26th, 2017 AT 7:22 AM
Tiny
CARADIODOC
  • EXPERT
Sounds like a good lace for a reputable person to open a shop, ... As long as there are mechanics around to hire who value their professional reputations.
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Monday, June 26th, 2017 AT 3:39 PM
Tiny
JESSE R. VALLANDINGHAM
  • MEMBER
Hey Guys, Just a quick update. I took my car to Toyota and after explaining everything I have done, we simply pulled the injectors and what a mess. The throttle body was full of buildup as well. Hopefully the lights will stay out now. Injectors are something that has to be cleaned the same time you change the oil or every six months which ever comes first because the fuel available in Nigeria is not the cleanest. Lesson learned.

Thanks again for your advise and inputs. Much appreciated.
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Wednesday, June 28th, 2017 AT 6:36 AM
Tiny
CARADIODOC
  • EXPERT
All right! One in a row! Happy to hear you solved it. I would not have come up with that solution.
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Wednesday, June 28th, 2017 AT 8:24 PM

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