Question Asked: Mass Air Flow Meter Replacement
May 27, 2010, 04:27 AM
OBD II DTC P0171 fuel lean bank 1, poor acceleration, poor fuel mileage. Worse when engine cold.
I have two 2001 Pathfinders. This one (P0171) was manufactured 09/2000. The other one (running perfectly) was manufactured 04/2001 and only had one minor problem which did not affect the operation in any way and was that the MIL, (Malfunction Indicator Light) which actually reads: "Service Engine Soon" had been illuminated on the dash for about 18 months. With the DTC code indicating fuel tank pressure problem (probable gas cap).
I swapped the Mass Air Flow Meter between the two vehicles (actually swapped the entire MAF/air filter enclosure assy).
Now the vehicle with DTC P0171 seems to have better acceleration, although the MIL is still lit on the dash.
Now the vehicle that was running fine has almost no power on acceleration and hesitates and cuts out at different speeds if the accelerator pedal is applied too much. The odd thing is that the MIL on the dash (probable gas cap) went out after being on continuously for 18 months.
I did a preliminary part number check at the Courtesy Nissan Website and both vehicles should use the same part number MAF so I am puzzled as to why the vehicle, which was running fine, should have such extreme power loss running with a MAF from my other vehicle (P0171) which only had mildly noticeable poor acceleration.
The pathfinder has a learning process for idle air flow and fuel/air mixture which can be initiated using the Consult II scanner, which unfortunately, I don't have. I do not know if the vehicle is capable of initiating the learning process on it's own nor what conditions will cause it to initiate the learning process.
When replacing the MAF on a Nissan Pathfinder does one have to do anything other than properly physically install it in order to get the ECM to establish the parameters for proper operation with a different/new MAF?
Thanks for your consideration of this puzzling symptom.
UPDATE: During a second trip the MIL on the dash would blink on or come on momentarily, then go off. The extreme loss of power continued throughout the second trip. After starting the vehicle and while waiting for the engine to warm up to begin a third trip, the MIL came on and stayed on. As I began driving I noticed that the vehicle now had the same symptoms that my other vehicle had, mildly noticeable poor acceleration.
Summary: It appears that during the first and second trip the ECM was doing it's best to cope with the malfunctioning MAF and when the ECM's efforts to adjust the air/fuel mixture went to the maximum limits without achieving the desired results, based on what the oxygen sensors were telling it, the ECM turned the MIL on and stored the DTC. Apparently it learned how to cope with the defective MAF and now the engine will run based on the parameters the ECM has established to cope with the defective MAF Meter.
I will now read the OBD II DTC and if the code is P0171 can I safely assume that the MAF (which was borrowed from my other Pathfinder with the DTC of P0171 stored) is defective?
A new MAF costs $442.03 plus shipping so I would really like to hear from you all on whether my analysis is valid or not. This is my Wife's car and she knows how to motivate me if you know what I mean. Please help. Thanks.
Question Asked: OBD II codes P0171 & P01140
May 06, 2010, 04:26 AM
Service engine soon light on and OBD II codes P0171 & P1140. "Fuel system lean on bank 1" along with "mass or volume air flow circuit range/performance problem.
This 2001 Pathfinder has 135000 miles on it and the Fuel mileage and engine performance are very poor when compared with my other 2001 Pathfinder which has 172000 miles on it. After I replaced the fuel filter and the air filter the service engine soon light went off for a few days, then came back on with the same two codes stored. When accelerating power drops off even more as soon as it reaches between 3600 and 3800 RPM. I checked all vacuum related hoses for leaks except the PCV hose as I cannot locate it. All hoses are in good condition and still feel nice and plyable and none touching where they can wear through from vibration. Used carb/throttle cleaner to try and detect a leak, however have not checked the intake manifold itself. With these two codes stored together would the highest probability be the Mass Air FLow sensor? Note that the new air and fuel filter on this Pathfinder is from Autozone, whereas the air filter on my good running Pathfinder is from NAPA. I can check the MAF voltages, however I don't have a scanner to check the barometric pressure or long and short trims. Would the MAF be the highest probability considering the symptoms I have described?
Question Answered: front side marker bulb replacement
November 11, 2010, 02:31 AM
It is not easy. The cover is stabilized by prongs which are part of the cover. These prongs resemble a rounded tapered arrow head and they are pushed into a part mounted in the light assembly. That part has an opening which is slightly smaller than the arrow head yet it gives ever so slighlty to allow the arrow head to be plastic pushed into it, then holds it firmly in place. The problem is that the arrow head is plastic and as the plastic ages it tends to stick to the part which holds the arrow head securely in place. I broke one of the arrow heads on my first attempt. I needed to replace the bulb on the opposite side of the car also, however, having seen how it was made and having broken one already, I was more careful with the second one. If you put any sideways force on it, it will break. After the screws are removed all force must be towards the front of the car with only minimal wiggling of the cover from side to side. You must find a way to apply enough force so that the cover moves to the front of the vehicle only until you loosen the grip that the ageing plastic has on the holding mechanism. With enough force, it will eventually break free. At the same time you must not apply enough force to break the cover assembly. If there is any way to get some WD-40 in there where those two parts meet, that would make it easier. Good luck.
Question Answered: Not staying cranked and shaking back end when driving
November 10, 2010, 06:46 PM
The "hold" light comes on whenever you press the button on the shift lever which turns overdrive on or off. Possibly you are not aware of this feature and accidentally pressed the button. This is a handy feature when driving in mountainous areas as it keeps the overdrive (highest gear) from engaging, keeping (holding) the car in the next lower gear so that the car will not upshift prematurely and lug down the engine while going over mountainous or hilly terrain. Press the button again and it should go off. I have no information regarding the vibration from the back. Hope this helps.
Question Answered: SERVICE ENGINE SOON Light.
May 28, 2010, 03:07 AM
The shop manual for the Nissan Pathfinder states that you can clear the OBD II DTC (Diagnostic Trouble Code) (which will turn off the Service Engine Soon light on the dash) either by using the Consult II diagnostic scanner tool or by disconnecting the battery for at least 24 hours.
It is not recommended to do this, however, until after you have resolved the engine control malfunction which set the light (and the DTC) on in the first place.
Even if you cleared the DTC and turned the light off, after similar conditions were encountered which set them on in the beginning, are encountered again, two times in succession, the DTC will be stored again and the light will turn on again.
If the engine control problem which set the DTC and light on no longer exist, the computer will turn the light off after several driving trips, provided those same conditions are not encountered again.