CEL P0171 Code ... need help with root cause for this

[MetrowestLara]

I have been getting P0171 Bank 1 Too Lean CEL code off and on for the last few months on my 99 3.0 SLE Cali-spec Solara. I have replaced the MAF Sensor, O2 sensor(near firewall), fuel filter, spark plugs, ignition wires, air filter and still have not seemed to go very long before this code comes back. Just today I added a bottle of Techron Fuel Injector cleaner to my gas tank when I filled up.

I'm trying to figure out what is causing this. When I get the code I can feel the car really get bogged down. It feels like it's being held back and fells really kind of jerky. I have searched the forum all ready and didn't see any post where they descirbed this symptom. I have replaced most of the things that could be a potential source of the problem.

Should I replace the O2 sensor towards the front of the engine? I'm not sure this would help since Bank 1 I believe is closest to the firewall and I replaced that O2 sensor already. Is this most likely a fuel injector problem hence the herky jerky feeling?

Any one who has had this issue I would appreciate hearing from you and what you did to resolve it. I really don' t want to throw more parts at it if it isn't going to solve my problem. Thanks for looking and responding.

[Eye8Pussies]

check injectors and also for vacuum leaks

[MetrowestLara]

The other thing I notices is that when the gas tank is full it seems to smooth out and my mileage seems to be wehere it should. As the tank gets lower, 1/4 or less the car really starts to feel jerky and you notice it more. Also the mileage seems to really drop when the tank is nearing empty.

Should I check all 3 injectors near the firewall since that is Bank 1 or do I need to look at all six? Also one of the possible causes is fuel pressure related. Can I do this myself or does it need a mechanic?

[MetrowestLara]

I had another question regarding this. My TRAC OFF light has come on in conjunction with my CEL light. Normally, when I get the P0171 CEL I don't have the trac off light on as well. I have seen this combination of warning lights when I had a bad O2 sensor. One of the causes mentioned in the P0171 code is a bad O2 sensor. I had previously replaced the O2 sensor closest to the firewall so I wouldn't think that this is the issue again. I replaced it with a Denso OEM brand sensor four months ago.

My question is, is the sensor near the front of the engine considered Bank 1 as well? The possible causes don't mention which O2 sensor could be causing the P0171 problem. I'm thinking that maybe this is what is causing the P0171 condtion as my mileage has started to really drop off. From what I read here, when an O2 sensor goes the car can run rich which causes the MPG to be affected and this is what I am seeing. I'm just trying to figure out which one I should be looking at. Thanks for the help.

[kwyse]

Hmm, interesting...I have a P0171 too and my TRAC OFF light is on too. I also have a P0125 and P0136.

P0125: Insufficient coolant temperature for closed loop fuel control. (I'm non-cali spec)

P0136: Heated oxygen sensor circuit malfunction (bank 1, sensor 2)

The TRAC OFF light didn't come on right with the check engine light. It came on the first time I started spinning my tires in the snow and it has came on ever since.

I'm taking the car in tomorrow to replace the O2 sensor, bank 1 sensor 1, because this is what the P0171 and P0125 have hinted at. My MAF has just been cleaned and I think the injectors are fine.

I'm a little thrown off by the P0136, but I'm thinking it may have been thrown by how rich the engine has been running; the exhaust reaks of unburnt fuel which is basically the repercussion of the P0171/safe mode.

I'll keep you posted with my progress, hopefully this gets taken care of tomorrow.

[NRDriver]

i get the po171 when i put on my CAI extension do u have one. i am a mechanic and i still havent found the cause of this problem. i have had a couple more experienced mechanics help me and they have no idea why this happens. i am thinking it has to do with the valve cover breather on bank one whick goes to the cai

[MetrowestLara]

I do not have a CAI installed. My engine is a stock Cali. spec engine. I reset the ECM and so far I haven't gotten another CEL light. It seems if the car doesn't want to run more than a few weeks before it throughs another CEL regardless of what I've replaced. Most times it's been the P0171. I did some Internet searching and from I've learned, Bank 1 O2 sensor is the one closest to the firewall and I've already replaced it. I'm hoping that it's not what is causing this problem since it was already replaced. Are the O2 sensors Bank 1 and Bank 0 the same part? I thought about buying another one and seeing if this really is the problem. It's been a little frustrating trying to nail this one down.

[kwyse]

After taking the car in today here's what I got. The mechanic said the first thing to do was to check for vacuum leaks and needed to remove the intake manifold to do so.

The P0300 came back (random/multiple misfire) so he was going to check the plugs and wires while he was back there. Another cause could be the coil packs in front. There was actually a TSB on them...free replacement for 3 years. Now they're $150 each, so hopefully its not them.

And I'm not sure the status of the bank 1 upstream O2 sensor. I'll find out more on Monday.

And I have a CAI...never had the P0171 before. Maybe there's a leak in one of the connections that were made during the install.

[NRDriver]

according to ALLDATA either bank 1 or 2 may cause this

[kwyse]

Ok, so here's what was wrong. I needed a new gasket for the intake manifold. That was where the P0171 was coming from. I also needed new spark plug wires. Mine were rotted out and causing the misfire code.

The upstream O2 sensor is working fine...the downstream one is working slow. I did not replace it now because it really serves no function other than environmental. I'll see if the P0136 comes back.

[dws1216]

I have the same issue. Did the gasket replacement work? What was the cost?

[Loss4wrds]

Which manifold gasket? The upper between the plenum and manifold or the lower between manifold and block/heads?

[Dawgz]

If ur gettn a System lean, a toyota tech told me to clean the maf with maf cleaner. It works, try it out.

[Eye8Pussies]

random misfires = vacuum leaks or maf problems.


usually vacuum leaks because then the maf readings don't equate to how much actual air the engine is actually gettin

[kwyse]

It was between the plenum and manifold. They also replaced the throttle body gasket. The cost was around $500.

But, the codes came back days later. When I got them read I still got the P0171, P0125 and a new one, P1133 which I think corresponds to the rear bank upstream O2 sensor.

The car is still running poorly, kind of stuttering especially at idle. When I got the reading the misfire codes had not reappeared. I'm going back to get it taken care of tomorrow so I'll keep everyone posted.