1995 3.0, Coolant Temperature Sensor

[MaverickH1]

Saturday my girlfriend and I jointly purchased a 4Runner to be a dog dedicated camping vehicle. It took me forever to find a local manual transmission 4Runner. Two things were obvious immediately, it was running very rich and the computer was throwing a 71 - EGR code.

I've been checking the EGR circuit for a couple of evenings with equipment that hasn't been very reliable and without being able to get to the VSV. Everything seems to check out.

Now my question... the EGR system gets its "orders" from the Coolant Temperature Sensor, does it not?

The truck, according to the gauge on the dash, takes a VERY long time to move from off of cold. The heat works long before it does move from cold. I'm thinking that the CTS is reading improperly and is causing EGR issues and feeding the engine too much gas.

I tried to get to the sensor last night for testing and can't seem to get the damn connector off. Of course, broke the little tab.

Would a CTS failure cause an EGR light to trip?

Would it be possible to check resistance of the CTS at the computer connection terminals instead of directly at the sensor?

Looking forward to being an active member here.

Mav

Picture of the lucky pups:

 

[nicnmike]

When I got mine, it did not have a thermostat in it and also took forever to warm up. When the engine reaches operating temperature, it goes into a closed loop mode.

 

[mikebontoft]

The coolant temp sensor is probably why it's running rich. you can test it by reading the resistance. It is pretty far back there though. You shouldn't have an issue checking it at the ecm either. just find the diagram for it and look for the sognsl and signal return for something like the "CLT." It sounds like it is not allowing the engine to come out of warmup enrichment though. replacement is likely necessary.

It also has nothing to do with controlling the EGR. Your likely problem with that is the egr flow or temp sensor thing, Mine had a wire jumpered on the harness side of the connector. I have since left it this way as it does not affect EGR operation.

I am very curious though... why on earth is the license plate up there? I guess I could see for towing, but it is also blocking the third brake light.

And welcome! it's my factory twin if it's a manual How many miles?

 

[MaverickH1]

haha

Welllll... the previous owners suck at putting in a screw. The license plate area had holes where it was either stripped out or had broken screws in it. So I had to figure something out to get it the 3 hours home.

I could have placed it in the rear window, but then I couldn't roll it up and down, and the dogs probably would have knocked it down. I could have zip tied it to the towing package, but then it would have been dangling lower than anything else, blowing around and at risk of being knocked off by road debris...

So it went there on the deflector temporarily.

As for the sensor... the diagnosis part of the factory service manual mentions the Coolant Temperature Sensor as part of the diagnosis of the code 71, and it says that the CTS basically controls the open/close of the VSV. The wording is so confusing... and they make a few typos... but it seemed feasible in my initial reading that both problems could come from a faulty reading of the CTS. I'll back probe it to see what kind of readings it gives.

It is a '95 5-speed. 187k.

 

[77'911]

Do yourself a favor and replace the t-stat(and coolant, toyota long life) which sounds like it is starting to fail which is probably tripping the enrichment code. If the O2 sensor has not been done in 90k, you might consider replacing that as well. If the fan clutch is failing, it can cause your truck to take a much longer time to warm up as well(just replaced one on our 4runner).
regards

 

[MaverickH1]

I just wanted to update this thread with what the root cause was:

I had discovered that the last person to plumb the vacuum system did it according to the aftermarket Chilton or Haynes manual or whatever it is. This plumbing was incorrect. Replumbing the vacuum system to the proper configuration according to the Toyota factory service manual made the code go away and stay away on its own for the last 9 months.

 

[Georgia Mike]

I know this is an old thread but it showed up in a Google search and I read through it. I wanted to thank you for updating it with the root cause of your problem. Unfortunately most threads never get updated to provide a solution. I was having very similar issues and your update prompted me to give my vacuum lines another look. They were misrouted and now that they're in the correct places it seems to have cured it.

So......THANKS! :trophy: