2007 Lexus IS350 fuel trims question

2007 Lexus IS350. Pictured is a screen shot of my scan data of the fuel trims after I replaced a Bank 1 downstream O2 sensor due to a P0137 code. What are the Short Term and Long Term trims telling me here? Can anyone lead me in a proper direction? Currently no codes but I think something is wrong. I don’t want to have to replace the entire “one piece” exhaust system for a bad converter if that is what this is telling me. BTW 114K miles

fuel trims at 2500 and WOT might give a better picture

o2 response tests might be in order also where are the millivolts ranging from 100 to 900 mv

You're definitely looking at a lean condition. If it hasn't set P0171 and/or P0174 yet, it will soon. :lol: Lucky for you, since both banks are running equally lean, you're likely looking for something that'd impact both.

Before we go wild with diagnostics, were you doing any repairs under the hood? No insult meant, it's just easy to leave a hose off during repairs and end up with fuel trim issues. FYI, nothing you were doing with the downstream sensors or the catalytic converters will cause this.

Standard fuel trim theory applies. When was this reading taken? If you saw these numbers at idle, raise the RPM to 2500 and check again. If they're significantly better, you're looking for a vacuum leak. If they didn't improve much or got worse, you're looking for a fuel delivery issue.

Tyler wrote: Before we go wild with diagnostics, were you doing any repairs under the hood? No insult meant, it's just easy to leave a hose off during repairs and end up with fuel trim issues

Just a question, how long does it take for long term fuel trims to be set? Can it happen right after leaving a hose off and idling the vehicle for a while?

Not immediately, it'd take at least several minutes of running. Toyota/Lexus is especially slow about learning long term trims, so it'd likely take quite a bit of run time to learn those values.

Interesting - thanks for letting me know
I might have to actually do a test one day - check long term trims then unplug an air line and watch how it changes.

Do iiiiitttttt. And let us know what you find!

A little background. This is my son-in-law's car so I don't have ready access. It required a new fuel pump last January. it was replaced and the shop said that there was low pressure but that their tester was bad. (So how could I believe the tester?) Car starts and runs great. This past July just before emissions test it popped a P0137 code. So I changed the O2 sensor. (Bank 1 sensor 2). It passed the emissions test. Then about 3 weeks ago the P0137 popped up again, this time with a P0430 (converter inefficiency). Since the O2 is warranted I replaced it again. Things seemed fine. Now the P0430 popped up again. I will probably get my hands on the car this weekend and try viewing the data at 2500 rpm and WOT. Also check for any and all vacuum leaks. If all looks good, what are the chances a fuel pressure regulator is kaput? Like I said car runs great. No bogging when flooring it at idle, etc and it has fantastic pickup. I'm stumped. (I'm just a retired dyi'er). Thanks for all help. Tony

I'll check this weekend and report back. Thanks for the tip.

TonyOle26 wrote: A little background. This is my son-in-law's car so I don't have ready access. It required a new fuel pump last January. it was replaced and the shop said that there was low pressure but that their tester was bad. (So how could I believe the tester?)

Do you recall if it was the high pressure pump (at the engine), or the low pressure pump (in the tank)?

This past July just before emissions test it popped a P0137 code. So I changed the O2 sensor. (Bank 1 sensor 2). It passed the emissions test. Then about 3 weeks ago the P0137 popped up again, this time with a P0430 (converter inefficiency). Since the O2 is warranted I replaced it again. Things seemed fine. Now the P0430 popped up again.

Gotcha. Thank you for the history!

I will probably get my hands on the car this weekend and try viewing the data at 2500 rpm and WOT. Also check for any and all vacuum leaks.

Let us know what you find. Here's a few SD videos that'll get you going in the right direction (if you haven't seen them already).

If all looks good, what are the chances a fuel pressure regulator is kaput? Like I said car runs great. No bogging when flooring it at idle, etc and it has fantastic pickup.

Unlikely, IMO. Aside from Toyota Sienna's, Toyota/Lexus fuel pumps rarely fail, in my experience. Not debating the last shop that changed the pump, just doesn't happen often. :silly: I'd also suggest putting the P0430 aside for now and concentrate on the trims. Once the trims are back in line, rerun the cat monitor and see what comes back.

Because you're not the driver, you might also ask your son-in-law if he's using E85. :blush: No insult meant, but it'd very quickly account for the lean trims.

High pressure. But my son in law says the guy at the shop told him that his pressure measuring tool wasn’t working properly. So given that, how can I say that the high pressure pump (in the engine compartment) is faulty. I think I need to do two things minimum. 1) recheck the pressure and 2) check guel trims at 2500 rpm and WOT. Thanks a bunch for the videos. I’ll check them out. Thanks!

No E-85. Strictly Shell Premium

You can skip a TON of fuel system testing by doing a WOT O2 test. In this case they're air/fuel ratio sensors, but the idea is the same.





The principle is to accelerate through 1st and 2nd gear at wide open and observe the upstream sensors. They should show rich. If they do, the fuel system is capable of keeping up with high demand. If they don't, then we dig into inputs (MAF), pirate air, and fuel delivery.

On this IS350, you're going to see the upstream air/fuel sensors represented by current data PIDs instead of O2 sensors with a 0-1V range. Not a problem. Negative current is rich, positive is lean. I don't have a WOT run from an IS350 in Global data, but this is one off a newer Highlander. The data will be very similar.



Ideally, both upstream sensors will show -1 mA at wide open. Equivalence Ratio PIDs will hopefully show .900 or less.

You can also observe Calculated and Absolute Load under the same conditions to gauge engine breathing and air measurement issues. Both should clear 85% at wide open when close to redline. Low Load indicates a breathing issue (unlikely since you noted the engine has good power), or a measurement issue (more likely, because of the lean trims).

Any luck with this one? Not nagging, just curious!

Sorry no update. I came down with a bad cold and wasn’t able to get my hands on the car for testing. I will update sometime this week if I can get out of bed. Thanks for your help