04 Tundra 4.7L Temperature gauge not responding

Hey all, I have a 2004 4.7L tundra. SR5, 4X4 crew cab.
Recently I hydrolocked my truck, and did a motor, trans and transfer case swap.
Upon the revival process I noticed my temperature gauge would flicker slightly between cold and mild, then after about 2 minutes would flatline and stay dead cold. The needle would slightly react to me tapping the dash where the gauge is.
I know it's not my temperature sensor, as I've tried the two I had and even bought another..
Any suggestions would be much appreciated!
Thank you in advance.

 

I'm guessing harness given what's involved with that swap (was it a 1-to-1 swap, direct bolt-in, no harness hacks needed?) but ...

I can't remember if the temperature is fed to the ECU first, then gauge, or to guage, then ECU.

If it's the former, do you have an OBDII tool that supports realtime feedback so you can see exactly what the ECU is reporting for temperature?

Doing this could eliminate the sensor and the ECU as the problem, may put the issue square on the wiring up to the gauge, and/or the cluster itself.

 

Depending on what year they may have changed it the gauge and the ECU have 2 separate sensors.

 

Thank you for your informative response!
I used the wiring harness that came with the donor engine/trans/transfer case to realize they had cut off 2 of the leads near the T-case end. I identified which leads they were and chopped out and spliced in the connectors from my previous wiring harness.
I also changed the ECU so the ECU matches the motor &power terrain.
Side note; My new Tcase has a wiring connector at the furthest end, but neither wiring harness had a plug for it.. Upon asking the previous owner about it he seemed to remember never having anything ever plugged in there, specifically because the connection for it on the Tcase for it is damaged and "has always been"
After some research I've come to find that it may be a speed sensor? It is still a mystery to me. (I've attached a photo of it )

I used my OBD2 live on my truck and it runs withing temperature spec!! I can't believe I didn't think of that.. thank you!
So this leads to my gauge or the wiring I guess..

@Nick, are you saying there is two sensors? Where would the one in relation to the ECU be located?
Thanks in advance!

 

When all else fails, look at what the ECU sees!

Glad you had a tool to handle it.

Note there is an EWD section so you can review wiring: https://www.tundras.com/threads/ultimate-tundra-wiring-diagrams-collection.81448/

You never said what year/make/cab type the donor engine came from, but you may want to yoink the EWD for that also.

I find the EWD are a PITA to read, but once you figure it out, it's not horrible. Realize the diff't cab types had slightly diff't wiring and harnesses.

 

Apologies, the donor motor/power terrain came from an 04 crew cab LIMITED 4.7L 4x4.. so same year just a different model. I'll take a lool at your attached files and see what I can make of it aha. Thank you!

 

Like you, I have an 04 and both sensors are beside each other on passenger side just below throttle body.

W 3(grey connector) Water Temp. Sender....for idiot gauge
E 2(black connector) Engine Coolant Temp. Sensor....input to ECM

 

You are the man! I'll try replacing the w3 sensor as I have not tried that

 

If you take off the intake tube, you should be able to see both the sender (for the guage) and the sensor (for the ECU) to the left (pass side) of the throttle body.

I have them circled for you in this picture. Ignore arrow. That was for another thread...


Here's part numbers from my 2000. Double check to make sure they are the same for your 2004.

 

It'll be really curious to see if this is just a case of the plastics cracking/connector not seating on the connector for the gauge cluster sender.

Or maybe it just didn't get moved over - wonder if you can borrow the one off the old engine?

 

I had to replace the plastic connectors for both sensors as well which wasn't hard at all. I just can't find what those part numbers are because everything is listed as "connector" in my emails.

 

Here's my cost of both from McGeorge Toyota.


Here's some connector part numbers, but I couldn't tell you what they are for. Maybe if you searched for these part numbers on the FSM in the EWD section.



I was tackling a bunch of different issues when I was placing these orders.

 

Here you go, Noah. Those last two are the only connectors in the list, and this is what each looks like. Seems the connector part numbers have a common prefix of "90980-" ?

 

The top one is for 4wd transfer motor. The bottom one is for the transmission temp sensor