I have a 2006 Toyota Carola Matrix Base model 186k that I bought at 180k. It keeps giving a P2238 code only when I accelerate under load. Usually on an on ramp or up a hill at higher throttle. So I'm getting a low voltage reading from the O2 sensor. It will go away after 3 starts or if I reset it and stay off if I don't push the engine hard. I replaced the o2 sensor with a Denso and it's still occurring. I have tested the sensor and the backprobed the circut while running. All seems good. Freeze frame data when the code is triggered is usually 2000-2500 rpm and only about 20-30 Load_PCT(%) so not at the higher RPMs as I would have expected since it is triggered by load. I knew I had some other exhaust issues that shouldn't affect this so when I did that work I took everything off, cleaned up the cat using a soap soak and diesel/cat spray on foam cleaner, and a short stint on acid, put on new manifold gasket and doughnut ring. Inspected the manifold. The cat wasn't too bad and I never had a cat code but thought I'd do that in case it was pressure related. Looked for intake leaks and didn't find anything with the break cleaner method. I did a live data test and the could not get the Load_PCT(%) to go above 76%. MAF at idle seems a little high, like 3-4.5. Long term fuel trim is 2-4% after cleaning air intake and fuel cleaners. Took the cat off and still same load max during test. I get mildy rough idle sometimes but not always, never dies though. What else could it be? 1. MAF???, 2. Some air intake leak I didn't find? 3. ECM? I've heard of ECM issues on these but I mentally want to deny this option..!!! 4. short in wiring only when hitting the gas hard? wiring is mostly in the harness but no wire issues I can see. 5. Injectors? I threw Bernie's cleaner in it and Berrymans B12. Helped idle a little bit. Scoped cylinders, they are in good shape and not much carbon (I replaced egr valve to be safe). At some point I'll have to just accept the engine light or pay a pro to figure it out but I don't really want to. I just have a cheap scanner you pointed out in the past.
My next step is to try a new MAF.
Thanks for the help.
With those raeadings I would get a factory denso MAF sensor.
It was original MAF of 19 years. I went to AutoZone and "rented" a duralast via buy/return for a test since no one in town has a Denso and they want 195$ to order. I did a test with it: 1. MAF reading seems lower and more reasonable. 2. No codes on on ramps. 3. better idle. 4. much more smooth shifting. 5. %load #s at full throttle went down to 72% which seems strange. Is this alright? So I ordered a Denso from rock auto for 111$. And threw in a 5$ intake gasket since these seem to have that issue. I've learned so much from you over the past few years. Thank you! I hear these have ECM issues and prior recalls through this process and found an online refurbisher for 100$ with 5 year warranty through eBay so that would be a final step if this code comes back. But I guess it could be the harness but there was no really low b1s1 o2 low voltage readings during live data tests ever (dropped to 2.8 for a second) so...??? would likely be the welds on the ECM.
Or I might look for grounding issues or it could be problems in the harness. Yuck. But it's looking good for now!!!