Toyota Sienna Forum - siennachat.com banner

1 - 7 of 7 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
Hello Everyone, hope all is well. I got a 2003 Sienna. I just put in a new O2 sensor ( Bank 2,Sensor 1) because I kept getting a P0420 code. I didn't mind putting in a new sensor even if it was not the cause of the P0420 code. ( The car was old enough to do a cursory change of O2 sensors. ) Anyways, the P0420 never came back after putting in the new sensor. The sensor was a Toyota OEM and was put in the bank 2, sensor 1 position. I also changed the PCV valve since it was on my list of to do things.

After driving around with the new 02 sensor, for about 5 miles, I kept getting P0174 (System too lean, bank 2, same bank as the new O2 sensor) , P0300, P0302, P0304, P0306 ( Random or multiple cylinder misfire) codes. I replaced all the 3 spark plugs corresponding to the codes ( The spark plugs had a lot of carbon fouling on them). I erased the codes and only the P0174 kept coming back.

After driving a few miles, the misfire codes also came back when I was going up hill.

Later when I removed the O2 sensor to give it a visual check, I noticed that it had major carbon fouling on it. ( It was in there for 180 miles of driving in city traffic).

Apart from putting in the new 02 sensor, new PCV valve and new spark plugs, I also started using full synthetic oil instead of conventional oil. I didn't do anything else new.

I also performed a Acoustic Control Induction System (ACIS ) actuator mechanism test as per my Haynes repair manual. After doing it, I noticed that the the rod being indicated by the red arrow in the picture moved only once, no matter how many times I stepped on and stepped off the accelerator pedal.

Could you please tell me what might be the issue here for the system being too lean and the misfires ?

Thank you for your replies and your time.

p.s. I have a OBD2 scanner that continuously monitors the car. That is the reason I am able to give you all the info.

stepford3.jpg
 

·
Registered
Joined
·
163 Posts
"Too lean" conditions are often caused by a vacuum leak. Un-metered air entering the intake after the MAF will cause this. Recheck the vacuum lines around the PCV valve(and the valve seating itself) where you were working. Make sure one is not now loose or cracked.


I got a "Too lean" code several years ago because of a vacuum leak at the hose connected to the front valve cover. The other end connects to the intake boot. At first, I couldn't see a problem at the connection. But after I removed it an inspected more closely, I could see that it was split and leaking.
 

·
Registered
Joined
·
163 Posts
In one of life's little ironies... my P0174 code is back!

When driving to Amarillo, my P0174 came back. This happened last year(or the year before) when I was driving to New Mexico. When I replaced the hose between the intake and the valve cover, I thought it was fixed. Apparently, something is still marginal. I think the problem is either a tiny vacuum leak, a marginal A/F (O2) sensor on Bank 2, or a marginal/dirty Mass Air Flow meter. My best guess would be that the A/F sensor is the culprit. It only affects one side whereas the MAF would after both. I am only getting a P0174 code and not a P0171 code(bank 1). Also, there don't seem to be many vacuum lines(other than the one I already replaced) that could affect only the Bank 2 side of the engine. I replaced the Bank 1 A/F sensor about 10 years ago when the heater circuit failed. Maybe it is time again....


I cleared the code, but it immediately returned in a few hours. I suspect that it will not return when I clear it back in the DFW area. My working theory is that lower air density of higher altitudes is enough to kick off the code. The only time I have had the P0174 code is when driving into much higher altitudes. Long drives to Houston and Galveston have not kicked off the code. The ECU can adjust the fuel trims enough at lower altitude to cover for a marginal sensor or leak. But at higher altitude it cannot.
More in a few days...
 

·
Registered
Joined
·
12 Posts
Discussion Starter #4 (Edited)
In one of life's little ironies... my P0174 code is back!

When driving to Amarillo, my P0174 came back. This happened last year(or the year before) when I was driving to New Mexico. When I replaced the hose between the intake and the valve cover, I thought it was fixed. Apparently, something is still marginal. I think the problem is either a tiny vacuum leak, a marginal A/F (O2) sensor on Bank 2, or a marginal/dirty Mass Air Flow meter. My best guess would be that the A/F sensor is the culprit. It only affects one side whereas the MAF would after both. I am only getting a P0174 code and not a P0171 code(bank 1). Also, there don't seem to be many vacuum lines(other than the one I already replaced) that could affect only the Bank 2 side of the engine. I replaced the Bank 1 A/F sensor about 10 years ago when the heater circuit failed. Maybe it is time again....


I cleared the code, but it immediately returned in a few hours. I suspect that it will not return when I clear it back in the DFW area. My working theory is that lower air density of higher altitudes is enough to kick off the code. The only time I have had the P0174 code is when driving into much higher altitudes. Long drives to Houston and Galveston have not kicked off the code. The ECU can adjust the fuel trims enough at lower altitude to cover for a marginal sensor or leak. But at higher altitude it cannot.
More in a few days...
UPDATE FROM ORIGINAL POSTER

My p0174, p0300, p0302, p0304, p0306 codes have been gone for a while now. My spark plugs are NOT carbon fouled anymore and my O2 sensor looks super clean. Do you want to know what happened?

I removed the ECU fuse, kept a cabin light ON and then went on and unhooked the battery negative terminal for 30 mins ( Removing residual power, if any, in the entire car). After much research, I learnt that when you put in a new sensor, the ECU needs to "re-learn" everything or else it will act as if the old sensor is still there. It has not way of knowing you put in a new sensor. You see, the ECU adapts as sensors change and get old etc., and by unplugging it, I made it forget all the old data related to the old O2 sensor and started it fresh all over.

Everything I wrote up there is a result of my careful research gathering information from reliable sources. Hope this helps.
 

·
Registered
Joined
·
163 Posts
2 weeks now after returning from higher altitudes in Amarillo and New Mexico, and my P0174 has not returned. I also found that P0171 had been set too somewhere after I cleared the P0174 code. So it looks like I probably have a slight vacuum leak or a marginal/dirty MAF that set the codes in thinner air. I'm not going to worry about it too much. I will clean the MAF when I get a chance. Maybe I will replace the PCV valve and all the short vacuum lines. A vacuum line could have a tiny crack. They are all original.
 

·
Registered
Joined
·
1 Posts
I am having a similar issue with the P1074 (bank 2 lean), P0102 (mass air flow circuit low), and P0113 (intake air temp). I cleaned the MAF sensor and put it back in. Wondering if that will solve this problem or should I be replacing the MAF?

Do you have any updates on your car from 2018? Thanks
 
1 - 7 of 7 Posts
Top