04 Toyota sienna A/F ratio sensor replacement

Status
Not open for further replies.
Joined
Oct 15, 2006
Messages
460
Location
Southeast
Hello fellow members! I have most likely an easy question for you. I have an 04 Toyota Sienna that has been popping an a/f ratio sensor code since October of last year. The car ran fine and I just got around to replacing the sensor Saturday. It was not driven until today. I cleared the code and now the car hesitates a bit on acceleration. It most likely needs a fuel trim (not sure if that's the correct term) relearn. I'm going to clean the throttle body this weekend when I have time since that seems to be a recommendation from internet searches. It was running completely fine until the sensor replacement so that's why I think maybe it was running rich prior to the new sensor. So far no codes have shown up and it's been driven around 25 miles or so. It will be driven around 75 miles total by the end of today. My question is will this be something the computer relearns on it's own as is or should I disconnect the battery for a bit to reset everything and start from scratch?
 
I wonder if cleaning the MAF sensor will help. It's a lot easier than cleaning the t-body esp w/dbw. I use CRC MAF cleaner available as combo pack at WM for $7. Also comes with a small can of t-body cleaner.
 
It takes a bit of time to relearn all the trims. I had to disconnect the battery for a while in my 2004 and do some maintenance. It idled quite low for a few days, but figured itself back out over time. 2005 sienna here. Same 3.3l engine.
 
I just cleaned the maf and t-body on the Matrix. I remember reading that the idle relearn is just to let it idle for 4 mins or so without touching the gas. Seemed to work fine.
 
Did you use a denso? known issues using aftermarket like Bosch. Sometimes they don't communicate well/calibrate with the Toyota ECU. If you removed the battery the engine could stumble as it relearns. That would indicate something awry like dirty TB, MAF, vacuum, etc
 
I believe this was a Denso sensor. I didn't check for any writing prior to installing it. It was running perfectly fine even with the code. It's something to do either with a relearn or just this sensor I'm thinking.
 
I don't remember the exact number to be honest. But when I searched the code back in October it was the Air/Fuel ratio sensor. If it pops again I'll post it. It was for the sensor that is on the front of the exhaust manifold and very easy to replace. My apologies I'm not much more help here
 
Check the intake boots for cracks, the two large hoses between the throttle body and the MAF sensor. I replaced a MAF sensor on a similar engine for nothing, it was cracked boots or hoses causing the whole problem. A code doesn't mean change that part, I learned that too.
 
Denso sensor comes in a Denso box which blue with "Denso" logo on a red box.
If not, it was not Denso. The part itself does not have any clear logo which is strange.

Also, when replacing parts, there are clips, tubes that has to be moved out of the way.
Make sure they are back on.
All the clamps for the accordion hose are tight.
The connectors are tight and make sure there is no frayed wires.

The rear Upstream Sensor is not easy to get into and replace.
 
Last edited:
Took my sweet time to change out my wife's battery on the Rav4 and it took about 200 miles for the computer to relearn. It drove fine at speed but really struggled to not stall out. Give it another 100 miles to relearn.
 
Originally Posted By: Leo99
Took my sweet time to change out my wife's battery on the Rav4 and it took about 200 miles for the computer to relearn. It drove fine at speed but really struggled to not stall out. Give it another 100 miles to relearn.


Next time let it idle for 5 mins and that should do most of the relearn. Then it won't struggle like that.
 
There is a TSB on this requiring an advanced scan tool to clear the learning memory but you can usually get around it by recording all settings then removing both battery cables, press the brake pedal for a sec then touch both battery cables together for a couple of seconds, the point to all this is purge off any possible residual energy from the system.

Pull the ECM fuse for a couple of min, replace and connect the battery cables. Start the engine let idle for 2 min then turn on the A/C and put it in drive, let it idle with your foot on the brake for 3 more min. Put it in park, turn off the A/C and let it idle 5 more min then drive it normally.

Do not drive it lighter or harder than usual, you want the transmission to learn its normal shift points. It will continue to learn over time but should run pretty much normally at this point.
 
Tried letting it idle for 5 minutes with no load before leaving work yesterday. No go there. But it's been around 100 miles since the change and it's definitely getting better. The issue only appears to happen in the 25mph-40mph-ish range. Under or over that shows no issue.
 
Toyota has a TSB about this, they require the memory to be cleared, the way I posted should clear the memory albeit not as easily as with a scan tool. Keep driving it and see how it goes you can allways do it if it still has drivablity issues.
 
Hey Trav it's still driving like crud. Could I accomplish the same thing by leaving the battery cables off the battery overnight and even a day or two instead of pulling the ecm fuse? The van is in for a recall right now but it'll be sitting at the house for a good couple of days.
 
If the van is in for a recall the dealer tech more than likely will run a "health check" in TIS Techstream and be alerted to this problem. Otherwise, do what Trav says and I like to turn the car on and let it be for 30-90 seconds to "zero" the DBW throttle, then start it and let it idle until the radiator fans cycle on in order for the ECM to learn its idle strategy. The rest of the OBD-II monitors(misfire, catalyst health, EGR, EVAP, O2/AF) will run as you drive.
 
It should,. after you disconnect the battery touch the cables together, this is AkA a cap discharge, it rids the ecm memory of stray data.
 
Apologies for the delayed response as life has been busy last month. I tried pulling the cables and touching them together with the brake pedal pressed for 10 seconds and no luck. I did go ahead and undo the battery cables just now and am going to let it sit for a day or two until I have to go somewhere again. I noticed that the intake cowl (if that's what it's called not only slides into the airbox up top but there is a spot directly below it's supposed to sit in. It wasn't in that good so I just fixed that too. Hoping that this fixes it. If not I'm going to move on to cleaning the throttle body and maf sensor as well as change out the air filter. Good news is that it's been around 2k miles and no code.
 
I just wanted to bump this one more time in case anyone else runs into this. I tried cleaning the throttle body, changing the air filter (which was dirty and needed it anyways), and running gumout in the fuel tank. Still no fix. So I broke down and ordered the Denso air/fuel ratio sensor. I just put it in and did the brake pedal/battery cable touch. Issue resolved. So don't be a dummy like me and cheap out getting a cheap overseas sensor. Get the OEM and do it right the first time
smile.gif


Edit: I checked the sensor that I originally put in and no Denso labeling. Thanks for the help everyone!
 
Last edited:
Status
Not open for further replies.
Back
Top