Toyota RAV4 Forums banner

1 - 7 of 7 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
Hello,
I have had an intermittent p0171 fault for about 18 months now. It seems to have started after I replaced a fuel pump. I cant remember how long after though so I dont want to jump to conclusions and say that my TOO LEAN fault is because of a lack of fuel pressure. I have cleaned the MAF sensor. Code went away for awhile but reappeared. I purchased a scanner and found the following:

O2B1S1 reads 3.2 to 3.4 volts. This seems wrong to me.
O2B1S2 reads 0.1 to 0.9. This should be the expected readings. I think...

Do I have a bad sensor in the S1 position? I also have other diagnostic data I could share. Please help!!
 

·
Registered
Joined
·
114 Posts
Hello,
I have had an intermittent p0171 fault for about 18 months now. It seems to have started after I replaced a fuel pump. I cant remember how long after though so I dont want to jump to conclusions and say that my TOO LEAN fault is because of a lack of fuel pressure. I have cleaned the MAF sensor. Code went away for awhile but reappeared. I purchased a scanner and found the following:

O2B1S1 reads 3.2 to 3.4 volts. This seems wrong to me.
O2B1S2 reads 0.1 to 0.9. This should be the expected readings. I think...

Do I have a bad sensor in the S1 position? I also have other diagnostic data I could share. Please help!!
I think both readings are normal just that the first one is for the A/F (air/fuel ratio) pre-cat sensor for bank #1 (A/F normal reading on Toyotas should be around 3.3 volt which is actually amperage but I guess its just reads in volt for the scan tool) and the second reading is for the post-cat oxygen sensor for bank #1 which normally switches between 0.1 and 0.9 Volt (switching between rich and lean condition). You should check the Short and Long Term fuel trims during the scan data reading and get the live data to show you the readings of fuel trims at different RPMs to see if it is a vacuum leak or the fuel delivery problems.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #3
Here is some more diagnostic information:

@750 RPM:
SHRTFT1: 1.6%
LONGFT1: 9.4%
MAF: 3.37 g/s
O2B1 S2: .780 V
SHRTFTB1 S2: 99.2%
O2B1 S1: 3.264 V

@2714 RPM:
SHRTFT1: 5.5%
LONGFT1: 18.0%
MAF: 8.06 g/s
O2B1 S2: .780 V
SHRTFTB1 S2: 99.2%
O2B1 S1: 3.404 V

@685 RPM
SHRTFT1: -1.6%
LONGFT1: 12.5%
MAF: 2.51 g/s
O2B1 S2: .720 V
SHRTFTB1 S2: 99.2%
O2B1 S1: 3.236 V

@2721 RPM
SHRTFT1: 3.9%
LONGFT1: 20.3%
MAF: 7.76 g/s
O2B1 S2: .820 V
SHRTFTB1 S2: 99.2%
O2B1 S1: 3.259 V

These readings were taken with engine cold(at idle and then at 2500RPM), then after it ran for about 20 minutes.
 

·
Registered
Joined
·
114 Posts
Here is some more diagnostic information:

@750 RPM:
SHRTFT1: 1.6%
LONGFT1: 9.4%
MAF: 3.37 g/s
O2B1 S2: .780 V
SHRTFTB1 S2: 99.2%
O2B1 S1: 3.264 V

@2714 RPM:
SHRTFT1: 5.5%
LONGFT1: 18.0%
MAF: 8.06 g/s
O2B1 S2: .780 V
SHRTFTB1 S2: 99.2%
O2B1 S1: 3.404 V

@685 RPM
SHRTFT1: -1.6%
LONGFT1: 12.5%
MAF: 2.51 g/s
O2B1 S2: .720 V
SHRTFTB1 S2: 99.2%
O2B1 S1: 3.236 V

@2721 RPM
SHRTFT1: 3.9%
LONGFT1: 20.3%
MAF: 7.76 g/s
O2B1 S2: .820 V
SHRTFTB1 S2: 99.2%
O2B1 S1: 3.259 V

These readings were taken with engine cold(at idle and then at 2500RPM), then after it ran for about 20 minutes.
You'll have to check the freeze frame data for this code P0171 (to see at what load the P0171 happened) but from these reading I would definitely look at the MAF sensor being dirty or some kind of fuel delivery problem. It looks like your car runs leaner under load, higher RPM your STFT and LTFT increasing. just take the MAF sensor out, spray it with the MAF cleaner let it completely dry and put it back. Re-test the readings and compare to these. See if you are getting increase in MAF b/s at the same RPM and lower STFT initially. If your STFT numbers go into the negative area it should eventually pull the LTFT down as well. If no difference after cleaning the MAF sensor I would probably have the Fuel pressure check done at the shop just to make sure your car gets enough fuel. I would first eliminate these two, MAF and fuel pressure and then proceed to the next step. Also, the dirty MAF or poor fuel pressure would affect both banks the same so make sure that the bank two fuel trims are normal, if they are you may have problem with vaccum leak or the oxygen sensor on bank one is not reading correctly.
Make sure your pos cat Os sensor (not the last one in readings that reads always around 3.3V, this one is the F/O ratio sensor but the one that reads O2S1 B1 0.720v, 0.820v and 0.780v this one is the one that supposed go from lean to rich always changing depends on the amount of oxygen in the exhaust. In Your readings it looks like this sensor is stock at always rich 0.7v to 0.8v. Make sure that at idle it oscillates between o.1v to 0.9v. If it doesn't this maybe your problem for this code and car running lean as well.

I have 2002 Rav4 and have the same problem, only that I think I have a vacuum leak most likely. Car drives very good but uses 30% more gas to run correctly. Mine also has a lean code on bank one P0171 but actually runs lean on both banks its just bank one runs way leaner than the bank two. Trying to figure out what's the problem, where is the leak but with no success so far. I hope this helps a little.
 

·
Registered
Joined
·
4 Posts
Discussion Starter #5
Ok, I did clean the MAF. It seems to have helped. When I first started car, it ran high idle(about 1500 rpm) for an extended period of time and then slowly came down to around 750. My STFT was way negative and slowly started pulling LTFT down into single digits. When I would run RPMs up to 2750, the LTFT would increase but only to around 12% instead of into upper 20s. More importantly, I hope I found the culprit. When taking the MAF off, I opened the air box to check air filter. When I popped the 2 clips open on the left of the box, I heard something fall. Looked and found a piece of broken plastic. Upon further inspection, I found that the 2 fixed clips or mount seats that the air box seats into on the right (before clipping the removable clips on the left) had broken. So the right side of the air box was not tight and may have let the filter to not seat properly allowing unfiltered air to pass over the MAF. I was able to seat the air box a little better and get a good seal, but I am going to have to come up with a permanent fix.

See attachment below...
 

Attachments

·
Registered
Joined
·
4 Posts
Discussion Starter #6
Here are some readings after the MAF sensor cleaning:

Load PCT: 15.3 %
ECT: 78 Deg C
SHRTFT1 0.0%
LONGFT1: 7.0%
RPM: 695
IAT: 53 deg C
MAF: 2.57 g/s
TP: 18.0 %

Load PCT: 13.3 %
ECT: 85 Deg C
SHRTFT1 -1.6%
LONGFT1: 11.7%
RPM: 3127
IAT: 55 deg C
MAF: 10.01 g/s
TP: 22.7 %

Read more at: http://www.obd-codes.com/forums/viewtopic.php?f=21&t=14846&p=52628#p52628
Copyright OBD-Codes.com
 

·
Registered
Joined
·
114 Posts
Here are some readings after the MAF sensor cleaning:

Load PCT: 15.3 %
ECT: 78 Deg C
SHRTFT1 0.0%
LONGFT1: 7.0%
RPM: 695
IAT: 53 deg C
MAF: 2.57 g/s
TP: 18.0 %

Load PCT: 13.3 %
ECT: 85 Deg C
SHRTFT1 -1.6%
LONGFT1: 11.7%
RPM: 3127
IAT: 55 deg C
MAF: 10.01 g/s
TP: 22.7 %

I am glad this worked out for you. The final numbers look good enough as at idle you're only at 7% lean which is normal for an older car. You still may have a small vacuum leak somewhere but anything under 10% should be alright. The closer to 0% the better. At higher RPM you're at 10% (11.7% - (-1.6%) = 10%) that is OK. How is your other bank 2? Also running lean?
 
1 - 7 of 7 Posts
Top