Question about 1997 Pontiac Bonneville

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Check engine light remains on. originally had P0171 code. changed vaccuum hose, air filter, also cleaned sensor. problem back. Looking for solution???

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  • Jeffrey Turcotte
    Jeffrey Turcotte Nov 09, 2010

    additional vacuum leaks are likely. Any leak that's on the engine side of the mass airflow sensor will cause lean opeation.



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I would recheck the vacuum. also if your brakes are harder to stop, you could a hole in the booster diaphram. if all that checks out then I would be looking at the exhaust before the sensor, and at the intake manifold for leaks. best way to check the manifold is to use WD 40, just spray it around where a suspected leak might be. If the engine smoothes out or runs a little higher that is where the leak is. Also you could have a bad sensor.
Good luck

Posted on Nov 09, 2010


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1999 Chevy G-30 utility van code p-0174 , cleaned then replaced MAFcleared code, back on 50 miles later, found vacum leak hose off vac. ball, code cleard 50 miles light back on,

what size engine do you have in the g-30 van. is it the plastic plenum. if it is there are rubber o-ring seals that go bad all the time and will cause the p0171,p0174,p0172,p0175 these are all lean codes also check for fuel pressure to make sure it is up to specs.
have you changed your fuel filter lately this can effect fuel trims.

Jan 09, 2012 | Chevrolet Cars & Trucks

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My 2000 dodge grand caravan 3.8 check engine light lit up and indicated p0134 oxygen sensor was replaced and light turn off 15 minutes later while on the road light turn on again put back on scanner now...

the codes for the oxygen sensors and egr valve dont neccassarily mean those parts are "bad". O2 sensor codes are usually caused by a different problem all together. There job is to monitor oxygen levels in the exhaust to make sure it is clean enough to meet emmisions standards. If you have a vaccuum leak, misfire, or a fuel problem those codes can show up. The egr valve recycles the exhaust gas in another attempt to clean the impurities. If the vavle was truley bad it would of affected the was the vehicle idled and drove on the highway. The egr activates when the throttle is depressed it opens at 1/4 of full throttle and closes at idle. Though they get pretty dirty the usually dont just fail under normal driving conditions. I would say that po171 code which if i remember right is a o2 sensor lean code, is showing now you have a tune up that needs to be done or a leaking intake manifold. A dirty or failed pcv valve can also cause that code because of it being operated by vaccuum from the engine. If any vaccuum is lost or restricted the hole combustion process will be incorrect.

Mar 10, 2011 | 2000 Dodge Caravan

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99 CHEVY trouble shoot code P0171

LEAN TROUBLE CODES (P0171 or P0174) A code P0171 or P0174 indicate the engine is running lean. This means there is too much air and/or not enough fuel. You can confirm the engine is running lean by looking at Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Normally, STFT and LTFT should be plus or minus 8 from zero. If STFT and/or LTFT are more than about +10 or higher, it indicates the engine is running LEAN. Negative numbers (-10 or more) indicates the engine is running RICH. A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

______________________________-- Causes A code P0171 may mean that one or more of the following has happened:
  • The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
  • There could be a vacuum leak downstream of the MAF sensor.
Possible Solutions Possible solutions include:
  • In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
  • Inspect all vacuum and PCV hoses, replace if necessary
  • Check for a dirty fuel filter and proper fuel pressure

Jan 02, 2010 | 2001 Dodge Ram 1500 Truck 2WD

3 Answers

Code reading p0171

So your car's CEL (Check Engine Light) is on and you had the codes scanned at a local parts store. Your car has either a P0171, P0174 lean fault code or both stored in the computer, these codes are based on Oxygen Sensor (O-2) readings. A lean code or codes indicate that there's too much oxygen in the exhaust. Remember parts stores have employees that have good intentions but they may not have the experience necessary to interpret what the trouble codes really mean. These codes are based on oxygen measurements in the exhaust. A common mistake with lean codes is to replace the oxygen sensors. This could be a very expensive mistake that will not fix the problem. Especially if both codes are present, because the chance of both O-2 sensors failing at the same time is very unlikely.
Most likely the cause is a vacuum leak. A vacuum leak can be caused from a vacuum hose, intake gasket or maybe even a leak in the air intake hose from the MAF (Mass Air Flow Sensor). Listen for a hissing sound that may lead you to the source of the problem. Some technicians will use a propane bottle with a hose attachment to help pinpoint vacuum leaks. With today's computers it's not quite as easy to check for vacuum leaks this way because the ECU (Electronic Control Unit) will compensate quickly for the added fuel and a change in idle is harder to notice. Oxygen sensor readings can be monitored with a scan tool while checking for leaks with propane, by looking for increased readings when enriching the mixture. Another way technicians can check for vacuum leaks is with a smoke test. By introducing smoke into a vacuum hose on the engine, the leak will be revealed when the smoke escapes from the problem area.
Aftermarket air filters that use oil on the element can sometimes damage the MAF. Over oiling the air filter may allow some excess to get on the MAF sensor wire or element. This can alter the reading, fooling the ECU into seeing more or less air flow therefore changing the air/fuel mixture incorrectly. I once worked on a car that would not start that had a problem with a MAF. When looking at the wire in the MAF, there was a burned piece of trash that made it's way past the air filter. After cleaning the sensor the car ran perfectly. The ash that was on the MAF sensor wire was altering the reading by enriching the mixture so much that the car could not run. After talking with the customer, he said the air filter was just changed. This was obviously when some trash got into the air intake hose that settled on the hot wire of the MAF.
Fuel Pressure could also cause a lean condition. If the fuel filter is clogged or the fuel pump pressure is low, there could be higher level of oxygen in the exhaust also. Most of the time though, the ECU will compensate for the reduced fuel volume. So this is one of the least likely causes of a lean code.

Nov 20, 2009 | 2003 Pontiac Vibe

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2004 denali check engine light stays on

There is no p01001, it's either p0100, or p0101.
Anyway, it's the mass air flow sensor that's bad. The p0171 and p0174 is a lean condition on bank 1 and bank 2, which are the oxygen sensors. Change the mass air flow sensor and that should take care of the p0171 and 74 codes.
The mass air flow sensor can cause the 02 sensors to read lean.
The u1301, is a class 2 circuit short to battery. That, you have to test wires to find with a voltmeter/continuity tester.
I would try and find that short before changing the flow sensor, you don't need the new one shorting out, they are not that cheap.

Nov 17, 2009 | 2004 GMC Yukon

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96 mercuy grand marquie check eng light, i get a p0171 and p0174 how do i fix this.

Could be the MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could also be a vacuum leak downstream of the MAF sensor which is more likely. You should inspect all the vacuum hoses and try cleaning the MAF sensor. Use only electronics cleaner to clean and let it dry before reinstalling.

If none of those work, then it may be caused by a dirty fuel filter or faulty fuel pump or clogged fuel injectors, but these are less likely

Aug 26, 2009 | 1996 Mercury Grand Marquis

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P0171 code on 99 Ford Escort ZX2 2.0L

Check vacuum hoses to MAP sensor. They can get porous after a while. Also check hose to EGR valve.

Jun 27, 2009 | 2001 Ford Escort ZX2

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Hi. You need to clean the Mass Air Flow Sensor.
This is an easy job.
Get a can of throttle body or brake cleaner spray at your local auto parts store.

Open the hood, and locate the air filter box. follow the tube from the filter box towards the engine. Look for a small black box with 2 screws holding it to the air tube, Remove the wire connector and observe inside the sensor with a flashlight. You will see 2 small wires, and they will appear fuzzy or dirty. Spray the interior with the cleaner until the wires are nice and clean. Do not use compressed air, you will damage the sensor. Put it all back together and drive it.
This will def fix your issue. This is a vey common problem. If you do it yourself, you will save 70 + bucks.

Thanks for choosing FixYa, and a FIxYa rating for my assistance would be greatly appreciated.

Jan 22, 2009 | 2006 Toyota Corolla

2 Answers

My check engine light is on!!

P0171 system too lean , bank 1
the most causes is :-
1- intake or exhaust leak . test the air filter in intake hose or
blocked exhaust pipe
2-MAF sensor (Manifold Air Flow sensor) locate in intake hose

3-fuel pressure or pump may be the filter blocked or need change
4- injectors may be need cleaning by use a cleaner with fuel

5-HO2S (Heated Oxygen Sensor ) locate in exhaust pipe bank 1 near the engine
check this causes , and ask for more information


Jul 09, 2008 | 2000 Hyundai Sonata

1 Answer

Toyota Avalon XLS, yr 2000, engine lights on

P0171 is a lean code. Open the hood, and locate the mass air flow sensor. Small black thingy in the intake tube between the air filter box and the engine, held in with 2 small screws. Remove the connector, remove the screws, and remove the sensor. Look into the sensor, you are going to see a couple of wires deep inside it. They will probabaly be "fuzzy" looking. Spray some brake cleaner on the wires until they are nice & clean. This will cure the P0171 code. Then check the air filter; replace it if it is dirty.

P1130 is an air-fuel sensor code, bank one, sensor one. More often than not, when we see this code, we replace the air-fuel sensor. Buy the replacement from you Toyota dealer, because the aftermarket sensors will not send the proper signal to the ECU, and you will be upset for having to buy a second sensor.

P0440 is a leak in the evaporative side of the fuel system; this looks after the fumes of the fuel in the tank. There are several reasons for seeing a P0440, like leaking vacuum lines, faulty fuel cap, rusty fuel filler tube at the cap, etc. This is kind of difficult to rectify without the proper equipment needed to diagnose what & where the actual leak is.
Hope this helps, please consider kind remarks regarding this solution. Thanks.

Jun 10, 2008 | 2000 Toyota Avalon

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