99-02 MAF upgrade / P0171 / 02 Sensor

[Wingnut]

Hey I'm a UY noob, fresh from YT. Thanks to Jamie (MTL) for pointing me this way.

Here is my issue, compiled from various posts & emails.

Got CEL.(back in January)
Code P0131: replaced O2 sensor with new URD unit.

Got CEL again immediately upon getting up to operating temp.
Code P0171:
*Checked for intake leaks: none
*Cleaned MAF, reset ECU (batt leads)
*Tested 96-97 MAF per FSM. Dynamic test was good. Resistance test was out of limits: reading 2088 ohms at 71.5 deg F. From the table below it seems it should read under 2000 ohms.
Info from the FSM:
AIRFLOW METER RESISTANCE TABLE
Temperature Ohms
-4 F (-20 C) ............................... 10,000-20,000
32 F (0 C) ..................................... 4000-7000
68 F (20 C) .................................... 2000-3000
104 F (40 C) .................................... 900-1300
140 F (60 C) ..................................... 400-700
176 F (80 C) ..................................... 200-400


Based on above information, updated airbox and replaced MAF with OEM to 99-02 style and repinned connector per ToyTech's UY thread. http://www.ultimateyota.com/index.php?option=com_smf&Itemid=26&topic=3915.0 (http://www.ultimateyota.com/index.php?option=com_smf&Itemid=26&topic=3915.0)

Still getting CEL with P0171, reset numerous times both with batt leads and OBD tester.

Tested ECT sensor, within specs.
Ran engine at idle, sprayed all possible intake/vacuum leakage points with carb cleaner while monitoring OBD readout on laptop, no noted RPM change.

INFO: The CEL is tripped after getting engine to operating temp (short drive) and stopping. When returning to idle, the CEL illuminates.

Hooked up the OBD again and noticed at that same point (return to idle) that the front 02 sensor voltage stays constant at .044 (or so), it does not fluctuate. Edit: Intermittently this voltage does fluctuate at idle, I just didn't happen to catch it with this particular screenshot. I noticed the CEL only comes on when the voltage stays constant.

Here are a few screenshots:
In this first image, the O2 voltage can be seen in red at the bottom. Notice the fluctuation when the RPM is revved, at idle there is no fluctuation.
http://img.photobucket.com/albums/v416/111db/02analize1.jpg


This image shows the O2 sensor in blue relative to fuel trim in red. Note engine coolant temp is normal.
http://img.photobucket.com/albums/v416/111db/o2graph1.jpg

I have not tested fuel pressure or the injectors, since I'm thinking any problem associated with fuel would be physically noticable: the engine runs fine.

Based on what I've read, I'm thinking the 02 sensor might be faulty, even though its brand new.

Additional info:



[size=10pt]Originally Posted by MTL_4runner
The voltage from a healthy O2 sensor (your 97 would have only O2 sensors, no A/F sensors) should look like a sine wave. I would have to say that the front O2 is your prime suspect at this point.

P0171 System too Lean (Bank 1)
When air fuel ratio feedback is stable after engine warm up, fuel trim is considerably in error on the RICH side (2 trip detection logic)

Here are all the possibilities: (my answers in red)
Air Induction System Leak (checked: ok)
Injector Blockage (not checked: but engine runs fine)
Mass Air Flow Meter (replaced with OEM new)
Engine Coolant Temperature Sensor (tested: within limits)
Fuel Pressure (not checked: no engine hesitation or issues)
Gas Leakage from the Exhaust System (see below)
Open or Short in the Oxygen Sensor or associated wiring (o2 works intermittently, so I doubt there is an open or short)
Oxygen Sensor Defective (new unit... possibly bad?)
Engine Control Unit (I hope not)


Ok the first thing you mentioned is what I was after: the 02 voltage should fluctuate constantly. And it isn't. I'll try some brake cleaner on it (again) and double check the wiring.

I know there is an exhaust leak (dang gaskets) but it is after the cat. I really don't see how this would affect the front 02 sensor. In addition, the list you printed I have seen in the 99+ FSMs... where exh leakage is a possibility. For my year (97) my FSM does not list exhaust leak as a condition for P0171. Oversight or Engineering change?

Additional Info
This is from the same test period as before, i just changed the parameters for the graph.

MAF only shows lb/min, not voltage. Probably the only output by the vehicle I'm guessing.

http://img.photobucket.com/albums/v416/111db/02-anylize-2.jpg

All the fuel trims:
http://img.photobucket.com/albums/v416/111db/fueltrims.jpg

[Wingnut]

Jamie and I have been PMing already, this is where we're at... my answers in BLUE


Ok, first, I made the assumption that you followed Toytech's MAF swap thread to a tee including swapping the pins on the MAF connector.

Exactly, this is the guide I used...

MAF thread:
http://www.ultimateyota.com/index.php?option=com_smf&Itemid=26&topic=3915.0

MAF connector pins stock:
http://i4.photobucket.com/albums/y147/phelix1976/IMG_2478.jpg

MAF connector pins with modified:
http://i4.photobucket.com/albums/y147/phelix1976/IMG_2484.jpg

If you didn't do this then that could certainly be your issue, if you did then it is possible the MAF is bad (unless it was brand new). If it isn't new, you may try a new MAF since they are relatively cheap since sometimes cleaning does not fix the issue.

So steps to fix:

1) Only if you still have it.......If you still have the old MAF setup and it worked, you might try reinstalling it just to verify if the issue is the O2 sensor or the MAF causing the issue. If you have the old setup installed and the O2 does not cycle at idle, you'll know exactly where the issue is.

I could do that, but as soon as I swapped out my original one for the upgraded one I was still getting the same code at the same time. This, however, was before I got my OBD test software

2) Check and double-check your new MAF's wiring! (if this is incorrect it may be affecting the O2 sensor wiring as well causing the weird graphs and strange output)
Pretty sure its right on because its pretty simple, but I'll double check tonight. {edit} - re-verified wiring is correct.

2) Replace with new MAF if you didn't already ($50 at the dealer, P/N 22204-07010 and that should keep...from saying the MAF is the issue)
MAF was brand new OEM, part number re-verified correct.

3) tell... you'd like to try another O2 sensor (double-check the correct part number when you get it!!!!) and have him give you credit for the "bad" or incorrect part, you need Denso P/N 234-4162 for the front O2 sensor if you have a 97, 3.4L, 4WD 4runner
The new one I recieved in January was 234-4162. I think its faulty from the manufacturer.

[MTL_4runner]

Jon, good to see you made your way over here and I'm sure you'll find quite a few sharp minds who can help solve some of the more challenging problems on these trucks. Given your answers above (you were still getting the code even with the old MAF setup and that the current MAF in your truck is brand new OEM), I am almost positive the last step will be the one that will fix your problem. As long as you are sure the wiring on the MAF is correct, then the O2 sensor is definately the culprit especially after seeing the graphs above.

[Wingnut]

Just for reference, do you have the FSM MAF resistance table for the later model? The one I listed in my first post is for the 96-98 MAF.

[MTL_4runner]

Just for reference, do you have the FSM MAF resistance table for the later model? The one I listed in my first post is for the 96-98 MAF.


Yep, here you go.

Temperature......................... OHMS
–20°C (–4°F)...................... 13,600 – 18,400
20°C (68°F)........................ 2,200 – 2,700
60°C (140°F)........................ 500 – 700

[Wingnut]

Well this issue hasn't gone away, URD support ignored my email from a week ago friday.

On another note, my battery gave up the ghost today, I noticed it was a little weak during starting over the last couple months. Any chance this could contribute to my problem? Might be a few days before I can get an Odyssee. My thoughts are that it would not be part of the issue, since as far as I know the alt voltage is fine.

[MTL_4runner]

Well this issue hasn't gone away, URD support ignored my email from a week ago friday.

On another note, my battery gave up the ghost today, I noticed it was a little weak during starting over the last couple months. Any chance this could contribute to my problem? Might be a few days before I can get an Odyssee. My thoughts are that it would not be part of the issue, since as far as I know the alt voltage is fine.


Battery is possible but not a likely culprit of the OBD code.

[Wingnut]

Finally got a chance to swap in a friend's 02 sensor.

No fix.

Back to the FSM... possibly fuel pressure/injector issue. Changed the fuel filter last night, will find out if that helps today.

[Wingnut]

I know you're all on the edge of your seats with my issue but in the interest of future troubleshooting for all toyotakind I will give you the latest... :)

Fuel filter no fix.

Was time for a new battery, installed a group 34 Diehard Platinum. Still got the CEL right after that, but only drove it once around the block until this weekend.

Went on a 200 mile offroad adventure over the weekend. About half way through I noticed the CEL was not on any longer. I wondered if 7500 feet altitude had any bearing on it but today I drove across town at 1300 feet and still no CEL. Yes I did a bulb check.

So in summation, I believe possible low battery voltage might have caused a momentary low fuel pressure tripping the CEL. I guess I'll never know for sure.