Hi All - long time lurker first time post.

My 2005 ES330, 135K miles, threw CEL, TRAC OFF, and VSC lights on Saturday. We were running errands and after a couple of stops they went off on their own. I went by O'Reilly to see if I could read anything and I got: P0031 HO2S Heater Control Circuit Low, Bank 1 Sensor 1. From searching on the forum it looks like I may need a new O2 sensor, the pre-cat one by the firewall. If it's the same procedure as in this thread: https://www.clublexus.com/forums/es3...00-w-pics.html then it doesn't look too hard.

Here's the interesting part. I have been having another issue, where when I accelerate fairly hard the car "pulses" like there is a tranny or fuel issue. I've had it checked at an Indy shop and they could find nothing wrong. When the VSC lights were on, the problem went away, and I thought maybe whatever was going on had finally hard-failed. When the lights went off the problem returned.

So, are these issues related? It's not the kind of driveability problem that I associate with O2 sensors. But since the traction control system was offline (I called the dealer and he says it does that when a CEL light is thrown) maybe that's a clue.

Thanks in advance for your help. The car generally runs great and I've kept up with regular maintenance and fluids, although not at the dealer. I would like to get this pulsing issue figured out, and I have nightmares of a tranny replacement.

 

I suspect that the problems are related. Remember the ECM uses data from the O2 sensor to regulate fuel flow. One possiblity, if it's getting bad readings from the O2 sensor then bad fuel flow and hence your pulsing. I suspect when the CEL comes on the ECM stops using the O2 data and reverts to the default. Thus you don't get the pulsing but you are not getting the most efficient fuel flow.

Go ahead and take care of the P0031. I'll bet that takes care of your pulsing.

 

Ordered a pair from RockAuto. Should be here tonight.
Got the Denso brand (OE) for $116.79 each.
Will post after install to let you know whether issue is fixed.

 

The rear sensor went pretty well, so I thought I was past the hard part. Did it from under the car and I didn't have much trouble.

But the front one - the EASY one - fought me the whole way. When I finally got it out, I found that I had galled the threads. So now the new one won't go in. I tried dressing the threads with a Dremel tool but no luck.

I'm going to get it towed to a shop tomorrow. This is beyond my skill set. I hope they can get it in without removing the manifold, or worse yet having to replace it. That would suck I'm really pi$$ed right now - I've done a boatload of repairs on other cars, including O2 sensors, and never had this happen to me before.

 

Wow that's really bizarre. Did you soak the sensor in penetrating oil before putting a wrench on it?

 

No, and that may be where I went wrong.

Both front and rear broke loose without much trouble. The rear came out by hand after that. But the front need a wrench at every turn. I did use PB Blaster when it first started to fight me, but I may not have waited long enough.

Really, I thought this was going to be a 1-2 hour job, max.

 

The shop was able to chase the threads with a tap and install the sensor. Total charge: $88. I found that many stores sell taps for these sensors; if I had known that I might have tried it myself.

The other piece of good news is that the pulsing has gone away, so Tom's theory was correct.