Another P0441 chase. A/F sensor at 0 volts?

[DerekRI]

Alrighty, another exciting P0441 thread, yay!

So, I bought '01 just a few weeks back. Clearly, the person I bought it off of had reset the MIL before I came to see it, because nothing was on during the test drive, but CEL and VSC / TRAC lights came on after my first couple trips since then.

I ended up buying a OBDLink MX+ once the lights came on, which is my first scan tool so I'm very new to using it (wish I had it for the test drive hehe) . The only code it is throwing is the P0441.

The vehicle runs well. Starts up quick, although it does idle higher than I would expect for longer than I would expect at startup. Nothing crazy, maybe 1200rpm. Idles at 650/700rpm at stop lights. I did notice while looking for vacuum leaks under the hood that a couple of the hoses aren't in great shape, and it's actually missing the 3" hose clamp after the MAF entirely, so I have some stuff on order for that. This alone could easily explain the code and the high(ish) idle at startup. I also bought a new gas cap from Toyota because I get a hard start ONLY after gassing up. I know this could be the canister / valve too, but I figured why not start with the gas cap for $30.

I was able today to plug the scanner in for my trip to the dealership, and monitor the O2 sensors readings... to my surprise, "Sensor 1" is never getting any voltage... like, at all. When I tried to graph it in the app, it didn't even register a reading for sensor 1. There was no flat line at zero volts, there was just no line at all on the graph for that sensor. I was really confused by this because by my (limited) understanding, I would imagine that no signal from the a/f would make this thing run horrible, or at least definitely throw a more specific code other than "pressure in evap system is off". There is no mention of it being in any kind of "default" mode that I can see. I have yet to get under the vehicle and check wiring / connections because it's raining out right now and I'm a driveway warrior.

I've searched the forums and the internet at large for "zero volts at air fuel sensor" and similar syntax, and haven't came across a thread where there was absolutely zero registration from Sensor 1. Just curious what it means to get no reading at all from an a/f sensor, and why it's not triggering a different code?

Thanks!

 

[Flya727]

Hello,

I too have a 2001 and I have been getting the P0441 and P0440 codes for a year. I have a scanner and just clear them. They usually pop up right after i fill the tank or i am getting near empty. Be aware that starting in 2001 they moved most of the fuel emissions stuff in the rear covered by your spare tire.

I’m going to be going through those vacuum lines and check the canister this week. I have no performance issues at all, just annoying to get the CEL every 400 or so miles.

Ill let you know if I find anything.

Rick

 

[DerekRI]

Yeah, my Runner is missing the spare tire so I've got lots of access up there. Looks to me like a lot of the lines have been replaced fairly recently, but I haven't gotten around to testing the valve yet. Tonight, I installed a new Toyota gas cap (although mine didn't look too bad), and a new clamp right after the MAF sensor. I cleared the codes and plan on driving around tomorrow to see if they pop back on or not. There are a couple more vacuum lines under the hood that could stand to be replaced, but I'm curious if the complete lack of a clamp after the MAF could have been the entire problem.

The information that I'm really looking for in this thread though is why a 0 volt reading from the A/F sensor wouldn't throw a specific o2 or A/F code? It is entirely NOT out of the question that I may just be using the scan tool incorrectly, as it's completely new to me.

Thanks for the reply, I look forward to hear how you make out

 

[DerekRI]

Just wanted to follow up with a quick update in case any one else is as noobish as me...

So, the default PIDs don't work for the A/F sensor, as they are set up for traditional o2 sensors. I looked through the Toyota PIDs and found the correct ones for AF Sensor Voltage. That, however, doesn't really help me diagnose anything because unlike the o2 sensor, the A/F just receives a relatively constant voltage from the ECU.

Either way, the A/F sensor seems fine, and that's why I was reading 0 volts initially. Sooooo much to learn about these scanners!

EDIT: Also, I've installed a new gas cap, and the 3" clamp after the MAF sensor, and the truck is running even better than before. However, I still have the P0441 code. I can see a couple more vac lines under the hood that are questionable so I'll work on replacing those. The lines back by the tank seem to have been replaced / repaired relatively recently (truck was inspected in January before I purchased it).