Elvota

Getting to work on my 3.4 swap. Not used to posting in this section with my '91 4Runner. Guess I am stepping up.

Short question: Does anyone know if the engine coolant sensor and water temperature sensor on a '96 3.4 send the same signal and monitor the same thing... engine temp? And how the fact that they are wired differently might effect things?

Long question: I am starting to figure out the wiring and this is my dilemma (you'll probably have to read this at least twice, cause it is as confusing as H )

This is what the engine actually has:

Engine coolant sensor is located at the top rear of the block. The sensor is self grounding, and only has one wire leading to it, which is yellow/red (Y-R).

Water temperature sensor is located at the top front of the block and has two wires leading to it. One is brown/ blk (BR-B) and the other is green/ red (G-R).

This is what the '96 wiring diagram shows: (which has been spot on for everything else so far):

Engine coolant sensor going to the ECU with two wires, not one. Two wires shown on the digram are G-Y (to G-R after plug) and BR-B. So, wiring diagram is showing me the two wires for the water temp sensor going to the engine coolant sensor... which is impossible. Coolant sensor has only one wire going in.

Backwards detail:


Now the wiring diagram shows the Water temperature sensor going to the gauge cluster with a single Y-R wire, where in fact the water temp sensor needs two wires.

Detail:


Now, if you have been able to follow this lengthy explanation you'll see that I have some conflicting information. Existing wiring patterns and colors don't match what the wiring diagram shows. I want to hook up the sensors correctly, and I am leaning towards ignoring the wiring color... but don't want to send incorrect signals to the ECU or gauge or worse blow something up.

Basically... I am confused on how the sensors differ (one with two wires, one with a single wire) and how this may effect the gauge or ECU.

WWYTD??

superjoe83

the single wire temp sensor is just for your gauge, it provides a variable ground to change what the gauge says, high resistance=low temp, low resistance=high temp

the two wire sensor is for the ecm, it shouldn't matter which wire goes to which pin

cam01

The water temp sensor (for the dash gauge) should be the only wire you have to mess with if your engine harness is complete. The coolant temp sensor (for the ecu) shouldn't be included in the wires that have to be spliced into. The water temp sensor comes through the firewall on pin 21 of the plug labelled II3 from the engine harness. That plug is the one with 26 pins total and the locking retainer on it. My paper copy of the FSM electrical wiring diagrams matches the pics you have posted. I have a complete uncut harness from a 96, 5spd 3.4 4runner laid out on the garage floor and the matching engine sitting on a stand beside it if you need pics of anything.

Elvota

Thanks for the explanation guys. Now I know what to do.

Yeah... uncut... that would have been nice. Was my goal to find one uncut, but didn't have much luck. I will say though that when I am all done with this project I'll know the engine wiring inside and out. Assuming it runs.

I may hit you up for some pics. Most of this is making sense so far... but you never know.

toyota_mdt_tech

You are confusing a gauge sender with an EFI sensor. EFI will be green, and 2 pins, gauge is a single pin. The EFI sensor gets voltage fromt he VC circuit, which means "voltage constant, it also operates the TPS and MAF sensors. As the impedance changes, it will show either a .5 volt for little resistance (short) , or 4.5 volts to show open or high resistance. See, a short "pulls the voltage down while little allows it to go up. If it sees 5 VDC, it knows the circuit is open, and 0 volts shows a direct short which by the way would disallow the check engine light and result in a no start.

The gauge is just a switch to ground, but a variable switch is all to move the needle which uses what is called a balance coils system/.