JBSTRD

I have a 2000 Runner, 3.4L, Manual Tranny, Cali Emissions, with 124,000 miles on the ticker. A while back I got a P0420 code and did a lot of research here looking for solutions. The engine fealt like it was holding back and surging slightly at times. I ended up just replacing the two cats with two Car-Sound Cats. A couple of weeks went by with no code.

Well, the CEL popped on as expected. I figured I was going to get a URD Sensor Sim to fix the prob since it is Cali Spec. Now the code is a P0171. Do you think I need AFM and O2 Sensors? The rig is still surging a little.

Thanks for any help.

toy_tek

Well I was going to start a P0171 thread tonight, but you beat me to it. I've read all the other P0171 threads, there is a lot of good info on YT already. You should check them out if you haven't already. I can give you my $.02 before I launch into my problem on your thread.

From my FSM:
Circuit Description
Fuel trim refers to feedback compensation value compared
against basic injection time. Fuel trim includes short-term and longterm
fuel trim. DTC P0171 is set when fuel trim is rich beyond a
certain value. Possible causes are:
* Air intake hose loose.
* Fuel line pressure.
* Injector blockage.
* Heated oxygen sensor.
* Mass Airflow (MAF) sensor.
* Engine Coolant Temperature (ECT) sensor.

toy_tek

Ok, here is a brief synopsis of my situation.

Got CEL.
Code P0131: replaced O2 sensor with new URD unit.

CEL again.
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 (link to thread)

Based on above information, updated airbox and replaced MAF with OEM to 99-02 style and rewired connector.

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, no noted RPM change.

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: Sometimes 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.



This image shows the O2 sensor in blue relative to fuel trim in red. Note engine coolant temp is normal.


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 is faulty, even though its brand new.

Any thoughts?

JBSTRD

Yes, I have looked at several threads relating to this issue. Feel free to post your situations as it may help me and others to diagnose our problems.

I am wondering if replacing the cats got rid of the P0420 code. I was expecting it to pop back up as a P0420 because I replaced the two cali emissions cats with two Car Sound Units. If the P0420 code came back, I was going to get the URD Simulator and call it good. But, now I am boggled since it is throwing a P0171.

Do you think this is a different prob all together or do you think this may be related to having two non-cali emission cats on there. Do you think this code would be fixed by the simulator, or does the simulator only take care of the P0420?

I am starting to wonder if I do actually need AFM/O2 sensors. Does the P0171 usually mean both sensors, just front, or just rear?

Sorry for all the questions, but I appreciate the help I am getting.

MTL_4runner

Jon, first let me say it is immensely helpful that you posted OBD graphs for diagnosis, I wish more people would. Second, the voltage coming from the front O2 sensor tells me that there is definately something wrong with it. It could be as simple as a wrong part number or the new sensor could be defective, but you'll need to do more testing to be sure that the O2 sensor is at fault and not clogged injectors (not likely or you'd have a misfire) or something else. 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:

• Air Induction System Leak
• Injector Blockage
• Mass Air Flow Meter
• Engine Coolant Temperature Sensor
• Fuel Pressure
• Gas Leakage from the Exhaust System
• Open or Short in the Oxygen Sensor or associated wiring
• Oxygen Sensor Defective
• Engine Control Unit

In your case I would expect to see the live graph of the O2 sensor look more like this (with an average around 0.45-0.5 volts):

toy_tek

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?

toy_tek

If you can hook it up to some diagnostic equipment that would help immensely. As you can see by Jamie's post, there are a number of conditions that will cause a P0171, but Cats aren't one of them.

Even with diagnostics, I'm having trouble pinpointing my issue. But its really just a methodical process of elimination. Ughhh!!!!

hross14

As a side note--when i got my injectors cleaned (off vehicle @ 165K) for my next project--the report came back that they were leaking and had a bad pattern. After cleaning they were excellent. Maybe it is time to clean them out?

Just an Idea

toy_tek

You mean running "fuel injector cleaner" through my system? Or taking them off and ???

I have a problem putting anything besides fuel in my fuel tank... but if it really helps the actual "problem" then I'll consider it.

MTL_4runner

Something is definately not right with that graph you posted of O2 voltage from the front sensor. As I mentioned, at idle it should have a nice sine wave pattern with the second O2 sensor reporting a fairly flat and relatively low voltage (indicating that your converters are working properly). Even while driving you should see the sine wave pattern on the front sensor continue unless you get on or let off the throttle rapidly.

An exhaust leak can cause the P0171 code as long as it is upstream of the sensor, any leaks after will not have any effect. Not sure why it is not in the earlier FSM because it should have an affect on both types of sensors (O2 or A/F).

Have a look at this diagnosis and you can see how to use the O2 voltage to find the issue (your case will be different):
http://www.troublecodes.net/articles...r_Review.shtml

Can you post a graph of side-by-side of the front and rear O2 sensor voltages for me at idle and while driving around?
I'd also like to see a graph of MAF voltage during an idle and drive around run as well (to be sure the MAF is working properly).

MTL_4runner

Running 3 cans of Seafoam in 1/3 tank will help clean the fuel system and may improve gas mileage. If you really want to have your injectors perform like new, then pull them out and have them professionally cleaned. I still don't think that is your primary issue because bad injectors usually create a misfire code as well.

MTL_4runner

I don't think you and 111db have the same issue.
Have you tried cleaning the MAF with brake cleaner as a first step?

JBSTRD

Yea, when I originally got the P0420 code I cleaned the MAF but the code came back. Since that was only weeks ago, I assume that is not the culprit. But, it is simple so I will probably try again.

If I had an A/F sensor or O2 sensor that was bad, would I know which one with the P0171 code, or could it be both?

MTL_4runner

Steps for your case (P0171) would be:

1) try to clean the MAF with brake cleaner again
2) if code returns, replace MAF (get a used one, new are big $$$)
3) if code returns, replace your front O2 sensor (Denso sensor only!!!)

toy_tek

Sorry, didn't see this last night.

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.

MTL_4runner

That's fine on the graphs if that's all you were able to log so far. Rear O2 looks fine. MAF output corresponds well to the engine's RPM so that's ok too. The front O2 sensor is still not operating normally at all, defintely still the problem IMHO. I hope other people are taking note of how useful these scan tools are for graphing outputs and problem diagnosis.

hross14

Yep, I ment taking them off and Having them professionally done. But he is probably right in saying there is some other problem.

Was just a side note

motoriderbc

Just thought I'd chime in. I'm a driveability tech by trade, here's a few suggestions for diagnosing a p0171.

1) Scan data is useless for verifying proper O2 sensor operation. It's not real time data. Basically the computer/scanner lags out and skips parts.

2) Fuel trims are your friend, they will give you direction.

3) Cleaning MAF sensors never fixes them, it may improve them enough to turn off the light etc, but they never work like new.

If you want to post up your a few saved screens, 1 at idle, 1 at cruise (50mph) and 1 saved driving at WOT at approx 4500-5000 rpm.

Make sure you include the fuel trims,maf, tps, iat

toy_tek

JBSTRD, did you ever figure out your issue?

Evidently mine was related to a weak battery. After I installed a new one, my CEL went away and hasn't come back. Go figure.

BigBallsMcFalls

OP

dude you just should have replaced both o2 sensors with dealer parts (or front
air fuel if you are cali spec) and you'd have been all set


it is 2008. these parts are what is due and failing for 1996-2001 toyotas.
the cats do not typically fail before the sensors


**and don't run any jimbo juice from a can in your rig. just gasoline. if you wanna try to clean something,
it doesn't come in a can. remove the parts and clean them with special equipment. fuel injectors
need to be pulled and put on a machine that runs solvent through them.


edit: I am probably wrong