Cat Therm. Sensor Bad? (1 Viewer)

[NocalFJ60]

I searched the list and got a lot of good info on the thermal sensor in the cat. I was checking the Air Injection System with the factory smog manual and my thermal sensor is reading open. The factory manual say it should be 2-200K ohms. I was on step 6 checking the thermo sensor to VSV1. When i short the thermo sensor air is not discharged from air bypass hose.

It looks like the sensor is bad. Has anyone replaced it? I called the dealer and Toyota has discontinued it. I have found some good after market cats but they don't come with sensors. Where is the computer this sensor goes to? Maybe it caused the sesnor to go bad or maybe my cat is gone and cooked it.

Thanks

 

[2mbb]

When I was trouble shooting my smog system a couple of years ago, I remember I thought my thermosensor was bad. I think I was also getting an open circuit reading. I cut the wires and pulled the thermosensor and heated it up on the kitchen stove. When I got it hot enough the switch started to close and read some resistance. You could probably try the same by pulling the sensor (don't cut the wires) and use a torch or other heat source. If your sensor is not getting hot enough (not enough air or fouled catalyst) the thermosensor may not test correctly.

I eventually got my car smogged by replacing the air pump and the cat. I don't know which was bad, I just replaced them both out of frustration.

IIRC, the "compter" is located behind one of the kick panels--I think on the passenger side. I think it's more of an analog computer (resistors and such) than a digital computer (1's and 0's)....

 

[Live to Ski]

Alrighty,

I am in the process of preping for smog. I know the test for the thermo sensor, but could someone enlighten me to as where the thermo sensor connector is located? I traced the wires from the sensor to a hole in the floor near/under the drivers seat. I really don't want to rip the carpet (bling) up, so if the connector location is set somewhere, that would be nice to know.

Thanks all.

 

[NocalFJ60]

You might need to take out the center console to get to it better. You will see when you pull up the carpet. You should not have to mess up the carpet to get to it.

 

[2mbb]

Yeah, the connector is under the center console.

 

[djawahir]

I just did the thermosensor test on my truck. On my FJ60, after letting her sleep through the night, I tested the resistivity of the thermo sensor. It read 'open'. I started her up that morning and tested the resistivity of the thermo sensor after about 5 minutes of running the engine and I got 50kohms.

So, it doesn't say it in the emissions manual, but I assume that if you are reading 'open' or 'short circuit' on the thermo sensor after warming up your engine, THEN you've got an issue.

I hope that helps the next person.

 

[Cruiserdrew]

This is amazing. I am trapped in the smog hell now as well. Sensor bad! I had CDan try and locate a thermal sensor for me-no go, as Toyota has none. Fornately Mudrak had one and I bought it from him. I also have a new Toyota cat going in today, and I replaced the smog hoses at the ABV as one was broken.

SO to pass somog this year will end up costing me about $1000, and that's with a truck that already runs and drives great.

 

[pismojim]

I don't understand how the thermo sensor would negatively affect smog tests. It's there to protect the cat by turning off air injection if the cat over heats. If it's missing or unplugged you still get the air inject that helps pass smog tests.

 

[Cruiserdrew]

I don't understand how the thermo sensor would negatively affect smog tests. It's there to protect the cat by turning off air injection if the cat over heats. If it's missing or unplugged you still get the air inject that helps pass smog tests.

Is this for sure? An open circuit in the sensor = injection all the time? That would be a good thing.

 

[NocalFJ60]

Is this for sure? An open circuit in the sensor = injection all the time? That would be a good thing.

Yes.. At some point when the resistance gets low enough it shuts the valve in the ABV. Without the sensor you should be getting air flowing down to the CAT all the time. If it is shorted due to a bad sensor then it would never let the valve open to get air down to CAT. If you got a good carb and are not running too rich it doesn't seem like the CAT would get hot enough to damage it anyways.

It is funny when I look on the date of this thread I started when I was looking into my sensor. It has now been 2 years and I still have not passed smog. But I have completely rebuilt my cruiser and am very close now.

 

[pismojim]

Andrew,

I also speculate that cat design has progressed since our cruisers were built twenty years go. The small lightweight high flow after market cat I bought a few years go is a radically different design than the huge heavy pellet filled monster it replaced. You can actually see through it. I suspect the overheating issues are, er... over rated.

Just look at the design of the cat(s) on your 80 Series. Notice there is no thermo sensor there either.

Cats like it hot. In fact, they require it. Yes, in theory they could melt down if they got too hot but the bigger problem is not being hot enough. The catalytic reaction necessary to clean your exhaust requires high temperatures. The optimal cat temps are ridiculously high. As I said, you are much more likely to have emission problems because your cat is not hot enough. (Take a spirited 20 minute drive on the freeway immediately prior to your smog test.)

My sensor has been disconnected since installing the new cat and I have always passed smog with flying colors. (Knocking on my wooden head.)

Maybe Mr. Toyota knows something. I can't imagine they would discontinue such a basic/inexpensive part if it was truly necessary to ensure compliance with emission requirements.

 

[Spike Strip]

I'm bumping this thread (and I'll link some others) to try and get a handle on how the THERMO SENSOR works in conjunction with the Air Injection system, and problems with my Air Injection system.

I find myself in Smog Hell at the moment. As with the OP, in post #1, I cannot get air to route through the Air Bypass Hose when shorting the thermo-sensor connector, as per the emissions FSM instructions.

Anyone else with that issue solve it? - it's independent of the Thermo-sensor, as it should ativate the VSV.

Other related links:

https://forum.ih8mud.com/60-series-wagons/25907-cat-therm-sensor-bad.html

https://forum.ih8mud.com/60-series-wagons/26670-tired-subject-need-thermo-sensor-help-please.html

https://forum.ih8mud.com/60-series-wagons/115749-catalytic-converter-oc-thermo-sensor-help.html

 

[NocalFJ60]

I would try bypassing the thermo sensor and the emissions board and activate the VSV manually and see if you get air from the bypass hose. If that works, chances are you have a bad emission board or loose connector.

 

[Spike Strip]

I replaced the VSV 1 and Thermo-sensor with good used units and I finally got the AI to function as per the tests in the FSM. I took the truck in for a pre-test and failed with high HC and CO at 15 and 25 mph on the dyno.

HC: 134/194 ppm - max 125/96

CO 3.77/3.16 - max .79/1.00

Gross polluter levels.

My take on this is with BOTH high HC and CO is it's running rich. Tech said as much. I just don't know what's going on with the AI system since it checks out as per the FSM

I guess I've got to look at the carb, or maybe the emissions board, as I've just about given up.