Code scanner showing high ECT readings

I'm confused, Guys. I had a CEL and read a P0420 code the other day. I erased the code and it hasn't been back, but I am playing with a new

$60 Foxwell NT301 OBD2 Scanner Live Data Professional Mechanic OBDII Diagnostic Code Reader Tool for Check Engine Light

Foxwell NT301 code scanner and was checking out the Live Data while driving down the highway. The ECT (F) was showing 397 degrees!!! WTF? Any idea what might cause it to think the temp is 397?

 

You're talking transmission temp, correct?

That sounds like the device is either picking up the wrong signal, or the conversion equation was entered wrong.

 

jbrandt,
I just drove it again and watched the live data. As I'm watching it, the temp (I'm assuming it's Engine Coolant Temp) is staying around 200. I recorded the data and played it back after I parked it and the playback is up around 380. I guess it's a problem with the scanner. Kind of had me worried for a sec. I was about to pop the hood and look for what all might have melted down on the test drive. I'm thinking my P0420 code might have been a hiccup of some kind. The code showed up just after splashing thru a water puddle after a long dry spell.

 

yeah, if your temp warning light isn't going on, too, that's a problem with the scanner.

The idiot lights on the dash "dumb down" the same data the scanner is getting. The dash doesn't show the minor temp variations until it goes over some threashold and is actually starting to overheat. The scanners show you the actual readings.

Was the P0420 code after seeing the check engine light (CEL) go on? Or was that showing up in the instantaneous scan readings? Again, if you didn't get a warning light on the dash, I wouldn't worry about it.

 

I noticed the CEL light on a couple days ago and then checked the codes on the scanner. The only recorded code was the P0420. I erased it and did a quick look for exhaust leaks. I didn't find any leaks and the code hasn't come back. The only thing I found that wasn't right was the air filter box door wasn't securely latched.

 

Usually the 0420 code is O2 sensors, or a bad cat. It may have been that you are right on the edge of needing a new O2 sensor and since you cleared it the sensor hasn't reached that threshold again. I think as long as you aren't getting that code again, you should be okay.

https://parts.olathetoyota.com/p0420-code-toyota

 

P0420 by itself is almost always related to a bad cat, O2 codes and exhaust leaks will usually trip a P0420 along with O2 sensor related codes like a P0141 or P0136...I had the P0420 that would come on/off by itself for the first few months but eventually it stayed on, new cats solved that problem.

From the link posted above..

As a general rule, if your engine trips a P0420 code along with other upstream trouble codes, the problem you're having likely isn't related to the catalytic converter.

However, if the P0420 code is the only trouble code - or if the other codes are all P042X codes - the likelihood of a failed catalytic converter is much higher.



See a lot of these P0420 threads these days in the 1st gen forum, these trucks are getting up there in age and considerable mileage so it's not surprising that the cats are starting to go out.

 

Thanks for the advice, Guys. With 230k on this truck, I'll be keeping an eye on it. I haven't noticed any decrease in power or fuel mileage, though.

 

It might just be that the cat is beginning to fail and the ECU only sees something wrong under certain conditions, over time (if it is the cat) it will get worse and the symptoms will begin to show more clearly. Just something to be aware of and prepare for since the code has already popped up once.

If you live in CA or someplace with similar emissions, this code equals = $$$ because CA compliant cats aren't exactly cheap. There are some affordable aftermarket options but they do not last long. Toyota OEM cats are superior to any aftermarket brand but cost about a grand each.

I went with CA approved Magnaflows since they were the highest rated of all the aftermarket brands, been about 2 years since I put those in and no more codes. Cost $600 to get both installed. Hoping to get at least a couple more years out of them

 

Good info. I'm in Texas, so the regulations aren't quite as strict. I'll be leaning towards using the Magnaflow cats, too, when the time comes. I've noticed they come in either direct bolt-in or a universal weld-in configuration and the weld-in option is about a third of the cost. You think the results would be just as good to have my local muffler shop weld in the universals?

 

I don't think it would matter assuming the actual cats themselves are the same, any muffler shop should be able to weld them in no problem. But that might make replacing them later more difficult/complicated than having bolt ons

 

At least with the Cat, it doesn't have any effect on mileage or power. It's simply to clean the junk that comes out the exhaust. There are 2 O2 sensors, one before and after the cat. The 2nd one basically just verifies the exhaust has been cleaned after going thru the cat. I believe the first one might actually have an effect on mileage since it helps control the fuel air (if I'm not mistaken), but then I don't think that throws the 0420 code, either...

 

nothing a little and can't fix, lol

 

I think I'll just go the bolt-in route. I'm not very good at welding thin pipe in cramped spaces and I like the idea of it being reverseable. Thanks for the help, fellas.

 

Quick update: I watched a couple videos and read a little more and then did a little more testing. I drove the truck a little to get up to operating temp and then checked out the scanner tool's live data and measured temps with a laser thermometer, before and after each cat, to come up with the following data:

The upstream O2 sensor fluctuated rhythmically between the values of about .05V to .75V while the downstream O2 sensor remained fairly steady at around 3.6V.

As for the cat temps Inlet/Outlet: Upstream cat: 260/460 Downstream cat: 400/310

It seems to me that the downstream cat is not doing anything and probably needs to be replaced. Looks like a weld-in is around $117 and a bolt-in is around $500. Let me know if you have any other thoughts or if I'm off base here.

 

That's exactly what you should see if the cat is working correctly.

 

Is it ok that I'm not seeing a temp increase thru the downstream cat? The outlet temp was actually lower than the inlet.

 

I can't explain the temperatures, but the steady downstream O2 reading means that the cat is doing its job. If it wasn't working then the downstream O2 sensor would match the upstream O2 sensor--same gases going in, same gases going out. That's when the computer throws the code for inefficient cat.