Hi, I am new to this forum, and new to the problems I am having with a 2000 ES 300 model. The errors that keep coming up are as follows: C1201 Engine communication circuit. P0420 Catalyst system efficiency below threshold bank 1.


Air filter has been changed last month, oil and coolant are alright. No apparent leaks. The battery might need changing, for example, the car didn't start 4 days ago, needed to boost it to get it going; has not been an issue since. However, the headlights and console lights will flicker slightly. I know this might be a battery issue.


The main issue is knowing where the Catalyst System bank 1 is located. I am no expert, and the Covid-19 pandemic has me strained financially. I have searched all over google for some schematics on where it is located, but with no luck. If anyone is having these issues, or a combination of these issues, I would greatly appreciate any help or guidance on what to do next. If we knew where this bank one catalytic system is located, we may be able to narrow down our approach. Our guess is that the catalytic converter needs to be replaced, OR the onboard CPU for the car might need work or changing, but like I said before, I am no expert and I want to gather as much information as possible from anyone who is more experienced in working with the ES 300 model. If I am way off on this, I would greatly appreciate any advice.


Be safe out there!

 

Hello and Welcome!

Any major car parts store should be able to load-test you battery for free in a couple of minutes. If it won't pass, you will definitely need to replace it. As for the flickering lights, I am pretty sure every 3rd-gen ES300 has that issue in one way or another - the stock alternator for those cars is too weak, 80A is not enough. What you can do about it is replace the alternator with the 100A one off of RX300/Highlander, which will not only solve the issue you currently have, but will also ease the load on the engine.

P0420 code doesn't always indicate a bad catalyst, it may also be a B1S1 A/F Sensor, B1S2 O2 Sensor, or the hole in the exhaust system. I am not an expert, but from my understanding, A/F sensor should give a relatively straight graph at around 3.2-ish volts. If it jumps around or completely stuck at some value (you have a completely straight graph), it needs replacing. Your car should also have an O2 Sensor right behind all the catalysts, which monitors if catalysts are working. Again, from my understanding, if everything is working as it should, the sensor should give out a reasonably straight line, since there should not be anything left for it to sense after catalysts. The diagnosis is pretty much the same as for the A/F sensor - if it is stuck or jumps around all over the place, it probably needs replacing. That said, if it is jumping in reasonable margins, then it is probably an inefficient catalyst that needs to be replaced.

As for the location of all the stuff mentioned above - here you can find a diagram that shows the location of the catalysts, and here you can find the location of all the sensors in the car. Bank 2 Sensor 1, as well as Bank 2 catalyst are located right in front of an engine. Bank 1 Sensor 1 and Bank 1 catalyst are located right behind the engine, underneath the intake plenum. Both Bank 1 and Bank 2 catalysts come together with their expected manifold as one unit. The last catalyst with Bank 1 Sensor 2 are located under the car, in the middle behind front wheels, the connector for the sensor is under the driver's seat.

P.S. To my knowledge, C1201 code is combined with a lot of fuel-related codes, so I would guess it should leave after the P0420 code is fixed.

Again, those are my guesses, I would appreciate if some can correct me if I am wrong..

Hope this helps and best of luck!

 

I appreciate your help. We are looking at the images and trying to match them exactly to where we need to be. I'm currently looking at the car and studying them with the images, so here goes. Everything you mentioned makes a lot of sense, since the mechanic I saw this morning mentioned the exact same thing about the graphs and when they need maintainence. I will try this out. Thanks again!

 

How many miles on the car?

How many previous owners?

How often is it driven and how many miles per year? Has it been sitting for a while?

Are you able to read and clear the Engine codes on your own?

You may wanna try clearing the codes, get the fuel tank to the low fuel level light, add some Techron Fuel System cleaner and fill it up with new gas. Then run the car through the whole tank, try to run the engine at full throttle a few times and take it on longer drives (20-30minutes). See if the code comes back.

Arsenii gave some really solid info. One thing to note is the O2 sensor voltage varies by the type of sensor in your car. Some came with Wide Band O2 (aka Air Fuel Sensors) and others came with regular O2 sensors. The Wide Band are more modern and more accurate, they were standard on California Emission spec’s cars. You can find out by checking the Emissions sticker under the hood and seeing if it has the letters CA on it.

 

i just recently changed out my bank 1 and bank 2 catalyst, Go to eBay and put in vehicle info. Purchase only Bosal cats. I made the mistake buying from a Canadian company and lost $650 I was past the amount of days given to file a complaint. Far as the other code not familiar
but bank 1 is rear of engine closest to firewall the front of engine is bank 2.
rear cylinder goes 1,3,5 odd numbers that’s why it’s called bank 1 I’ve attached picture

Bosal fits perfectly. Takes the OEM bolts and studs so have ready.

 

280,000 miles approx. I am the second owner of the car. It is driven about a 20 to 30 minute drive every other day. Yes, and have tried this, along with using the cleaner. That was all done just now actually, and I have no idea how long it takes for it to take effect. Since this is the first time this problem has occured, we figured it just might need cleaning. So we did just that. We knew also that there were mixed reviews for using a cat. cleaner, and most people say that is just doesn't work and saving money for a new cat. converter is always best; correct me if I'm wrong.

Also, we are going nuts over here. A user uploaded a photograph of the cat. bank 1, or its what I think to be the cat. bank 1 part we are focused on at the moment. Or am I getting the parts confused. I really don't want to drop over $500 and buy the wrong part, I really want to get this one right. I appreciate everyone who has replied. This is eye opening.

I am going to check under the hood for those digits, thank you for that, that is really good to know.

 

I did not know that. Thank you for the heads up. Did you have the exact same problem I am currently having? And if so, how did the problem sort of manifest itself to where you began to address the problem. For us, the check engine light and the Track off light came on nearly at the same time. And every time we added a fix, they came up again and again.

 

yes check engine light was on and traction control light was on. I cleared codes then it returned in about 5 minutes. I started by changing the spark plugs , the ignition coils and the fuel injectors also MAF sensor and bank1 sensor 1 oxygen sensor. Nothing working. Lol. Then ordered the bank 1 cat but it’s not the exhausr manifold. There’s a crossover pipe with small cat as provided in picture I sent previous comment. When I checked my bank 2 exhaust manifold cat it was loose inside it should be loose. So had to put job on hold and order. But I explained the pipes and weld job from the company I ordered from out of Canada sucked. I should have known better and ordered it Bosal and I did on 2nd attempt. Also get 2 o ring gaskets and gasket to flange before 3rd cat under cat. I didn’t replace that cat. All in all runs like a new Lexus and fuel economy is 28 mpg on highway 23 in city.

 

I see. Same exact thing happened to me, and everything else. I wanted to make sure, it seems like 100% the cat bank1 is the problem on my end. Obviously I cannot buy the exact same one you bought, and that was probably some time ago. Can you give me some pointers where I can purchase a new cat. bank 1, at a store front or online where it is OEM, or something that is safe to use that is not OEM if it exists?

My issue here at this point is buying from the right spot, because money is really tight right now and I need to make this count.

 

apply for their credit. Purchasing from Bosal is your best bet cost wise and certainty it’ll fit accurately
going to deal or is toooooo expensive it’s $1200 I already got prices from 4 Lexus’s Do not buy the Canadian exhaust crossover pipe.
these are the prices I paid not bad. Those are all the parts I purchased with the dates this yr.
remember you have to either reuse or purchase new studs. Use PB blaster lube on nutz the day before you do job and have a breaker bar mines 18 inches long 1/2 And spray the nuts aren’t rusted on the studs. Luckily mine weren’t at 170,000 miles

 

I appreciate your ongiong help on this matter. I need to get to work. Only time will tell if this fixes the problems on my car. I'm sure there are other ones, but this one is the biggest right now. Have a great day, kind sir.

 

He's from CA though, and the Bosals above are for the fed models, so he's facing a ton more $ for the cats (CARB-compliant).

 

I honestly don't know what you mean by this. Could you explain why he must pay more? And does this mean I'm going to pay more? I reside in CA as well.

 

California regulations prohibit the sale of most aftermarket catalytic converters to CA residents. That’s the reason that most of the listings say “cannot ship to California”
As for why, I won’t step into that morass.

 

I was referring to you because your location is listed as CA...California (yes?). What "he," 75damien, from AK (Alaska) posted was for federal models, not CARB (California Air Resources Board)-compliant, so no good for residents of California.