Somewhere I was reading that replacing the coolant temp sensor may help my gas mileage. Does anyone know anything about this? If it may help, does anyone know where it is on the 3.5? Or do you guys think I should just return it and get my 30 bucks back? Thanks
Modified by nmpath at 6:31 PM 1/6/2009

Im gonna have to bump this, Id like to replace mine and cant find a lick about it in the FSM or its location or how to change it.

Im assuming coolant is going to be coming out of this sensor when I remove it...

It's in the electrical section of the FSM, in the bit about gauges.


Chuck

Is there a way to search Adobe PDF's entirely for a certain word?? I have to search each category (engine mechanical, cooling and heating etc) categories individually and I never thought the sensor would be in the electrical section I guess

There is an index for the FSM.

Use Adobe's search function there.

Engine Cooling System, page LC-19, number 7 on schema.

CanuckQx4 wrote:Is there a way to search Adobe PDF's entirely for a certain word?? I have to search each category (engine mechanical, cooling and heating etc) categories individually and I never thought the sensor would be in the electrical section I guess

If you have Adobe Acrobat (the priced product, not the free reader) you can build an index across multiple files.
This can be very handy.


Chuck

nanit wrote:Engine Cooling System, page LC-19, number 7 on schema.

wow that sucker is gonna be HARD to find and get at eh



And this is on the BACK of the engine against the firewall??

Looks like you right. Maybe, if you remove intake collector assembly, it simplify the job?

Your lookin at 2-3 hours to have a shop do it.

Really the intake manifold has to come off ??

I guess Ill have to take a hard look at it from top and bottom to see if I can even see this sensor. Id like to do it myself

What makes you think you need to replace it?

My read on the '01 FSM says there are two sensors:

1. "Thermal Transmitter" which feeds the temperature gauge. This has a Yellow with Red wire, and connects itself to
ground, presumably through its threaded connection. See page EL-99 or EL-525. There's a picture of where its located
on pages EL94 and EL-520

2. "Engine Coolant Temperature Sensor" which feeds the ECU. This has Light Green with Red, and Black wires. See Page EC-167 and LC-18. You can read out what this is telling the ECU with an OBD-II reader.

Chuck

Well I did this test today, probed for voltage at the end of the female #3 pin connector, the test says I should have 5V at that pin, I have 4.8 so I think it should be fine



The problem stemmed from my temperature gauge reading incorrect, as soon as I turn the ignition on, it goes to half up the gauge, even if the car is dead cold and frozen, then when I drive, it pegs out to HOT. But I dont think its actually overheating or even getting up to operating temp.

That was testing the one that feeds the ECM, not the temp gauge. I'd get an OBD-II reader and get it to tell me what
the ECU thinks the coolant temp is (my AutoTap will do that). And to double-check, it was the Light Green with a Red
stripe wire that you measured.

Since you are getting clearly weird results from the gauge, I'd check it's transmitter. Page EL-108 in the '01 PF manual.
When you hear hoofbeats in Wyoming, think horses, not zebras.


Chuck

EDIT: I do infact have 5v at that probe point. I was measuring the 02 sensor or someting the first time, thanks for posting the wire color or I never woulda thought I was checking the wrong connector, didnt notice that one tucked away, pic is decieving!

Try this one on car:

How would you do that test on car?? I cant even see this sensor at the back of the engine

Dont get what you mean by on car though

Manual suggest to test sensor in boiling water off the car. My suggestion is to connect multimeter to terminals 2 and 3 like here

CanuckQx4 wrote:Well I did this test today, probed for voltage at the end of the female #3 pin connector, the test says I should have 5V at that pin, I have 4.8 so I think it should be fine



The problem stemmed from my temperature gauge reading incorrect, as soon as I turn the ignition on, it goes to half up the gauge, even if the car is dead cold and frozen, then when I drive, it pegs out to HOT. But I dont think its actually overheating or even getting up to operating temp.

Then start warmed engine and monitor resistance. Manual says that you should see something like 0.23-0.3 kOhms.

Well after making sure terminal 3 did have 5V, I went to this next test



Then I went to the next test which was to check continuity between terminal 2 and ground. Put the positive probe in the test slot of terminal 2, and the negative probe to my battery ground. I got .3ohm resistance

Try meter/gauge operation diagnostic procedure described at EL-124 of Electrical System manual.

.3 ohms is pretty close to continuity. But that's not testing the sensor for the temp gauge.

What nanit said, except that mine starts on Page EL-94 or EL-520 depending on VIN number. That's in the '01 PF FSM.
QX4 FSM may be different. It's the "Meters and Gauges" in the Electrical Chapter.


Chuck

My 01 qx4 manual muist be completely different as none of those pages are anything related.

Id imagine the clusters between pathfinders and qx4's are quite different??



I cant see a test here but its related to the gauges

I should mention this is a different from factory gauge cluster aswell. When i bought the Qx4 it had a cracked lense, well it was cheaper to just buy a new cluster from a 2wd off ebay then repair it. But it did this same problem on my old cluster aswell...

If that rules anything out

Since it did the same thing on your other gauge panel, it's likely not the gauge panel.

The very last thing in the '01 PF FSM EL Meters and Gauges section, is how to test the Thermal Transmitter. You use
an ohmmeter to test the sensor. At 60C (140F) it should read 170-210 Ohms. At 100C (212F) it should read 47-53 Ohms.
It's too bad they don't have reading for it cold, but I'll bet it's 300-600 Ohms or so, and yours will read less than 200.

I'm not sure where that thermal Transmitter is. I went out to see if I could get you a cold (by Calif. standards) Ohms
on it, but I couldn't find anything that matched the picture in the FSM. I didn't pull the plastic cover off the top of the
engine, though.

One approach would be to check it from the wires side of the plug that goes into the back of the gauge panel.


Chuck

Ive got to take lessons on how to read a FSM you guys make it seem so easy!!

I just want this damn gauge to rear proper again!! I have a feeling its screwing with my performance and fuel trims reading so high

Thanks so much for your help so far!!

I found the connector to the Thermal Transmitter for the gauge. It's pin 1 in the connector you checked pin 3 on. You
want to measure the other side (where the wires run behind the engine this time). Measure the resistance between pin
1 and a good ground.

It looks like the sensor itself is behind the engine and a bear to get to.

I found it by looking at the wiring harness layout. There's one at each end of the two big sections of the EL PDF.

Gotta go change the oil.


Chuck

OK I will do that test first thing in the morning and take pics since they show exactly what Im doing lol

And like you said about the sensor itself, I cant see the damn thing, how is it possible to replace it easily? Does the intake manifold have to be removed??

I'm not sure about how you replace the Thermal Transmitter, but I 'd start by having a look from under the truck. If you
have to pull the manifold, this would be the time to do the "Thread Locker on the Power Valve Screws" too. And before
you pull it, put an OBD-II reader on with the engine hot, and read out what the ECU thinks the engine temp is. That
sensor is back there too.

Chuck

So, has anyone ever replaced and/or have a step by step procedure for replacement of this sensor. I would like to replace as well but seems like too much of a task.