RB 25DET Swap Temp Sensors

ONLY for ADVANCED technical discussion about the 240sx!
[email protected]
Posts: 9
Joined: Mon Dec 30, 2019 5:28 am
Car: 1994 Nissan 240sx RB 25 DET swap

RB 25DET Swap Temp Sensors

Postby [email protected] » Tue Dec 31, 2019 5:29 am

My son purchased a 1996 240 SX with a RB 25DET swap. Previous owner has the cooling fan relay wire grounded so the fan runs continuously. We want to put it back to stock function. We reconnected that wire back to the relay but when we run the engine up to 200° the fan never comes on. So we are now troubleshooting all the temperature sensors on the car and wonder if there are more than the two that we see? There is one single wire sensor that is for the dash gauge. Then there is the two wire sensor that is for the ECM. Is there a third sensor by chance that serves as a switch to turn on the fan when the engine reaches a certain temperature or does that function take place with the two wire sensor that feeds the ECM? We know that the fan does work we are just trying to find out why it is not getting the signal to turn on.


User avatar
NukeKS14
Posts: 46
Joined: Wed Apr 10, 2019 2:50 pm
Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: RB 25DET Swap Temp Sensors

Postby NukeKS14 » Tue Dec 31, 2019 10:48 am

Recommend keeping your issue consolidated under a single post so that people trying to help have access to all of the relevant info. Read my reply in your other thread.

Direct reply to this one; no. There are only the 2 temperature sensors. The 2 wire is what the ecu senses temp by and would base the fan function off of.

No telling how the motor was swapped in. The harnesses are not plug and play so something was done to adapt the rb harness to the s14 chassis. Its likely somewhere in the adaption is where your problem lies. There are nissan fsms on this site. You want to get one for the 96 chassis and generation the harness is from you're running on the engine to cross reference where the fan wiring should be connected.

That would be the right way. Cheaper alternative would be to buy an adjustable temperature switch and wire that up to trigger the fans.

[email protected]
Posts: 9
Joined: Mon Dec 30, 2019 5:28 am
Car: 1994 Nissan 240sx RB 25 DET swap

Re: RB 25DET Swap Temp Sensors

Postby [email protected] » Tue Dec 31, 2019 11:33 am

thank you for your reply and your advice. I am new to this site and did not know where to post it since there is not a separate forum for RB 25 swaps.
The car still has the original electric fan and I'm assuming the original wiring harness because it snaps right in and The harness itself is all integrated into Another part is all wrapped in black cloth/tape.
To get it to run, the previous owner grounded one of the fan relays so it it is in constant run mode.

User avatar
NukeKS14
Posts: 46
Joined: Wed Apr 10, 2019 2:50 pm
Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: RB 25DET Swap Temp Sensors

Postby NukeKS14 » Tue Dec 31, 2019 12:10 pm

Welcome.

Yeah the part that connects between the ecu harness and the chassis is what would have been modified. Guessing previous owner did not connect the portion that controls the fan. He knew it and bandaided with the ground wire.

https://www.google.com/url?sa=t&source= ... 2jk-qhpXD-

You could use something like that to control the fans independently or download the fsms or search out a wiring diagram for rb25 to s14 swap and comb through what the PO did. The potion of the harness im talking about is in the pass footwell behind the ecu. It goes through the firewall there and connects to the chassis and ecu. Good luck.

[email protected]
Posts: 9
Joined: Mon Dec 30, 2019 5:28 am
Car: 1994 Nissan 240sx RB 25 DET swap

Re: RB 25DET Swap Temp Sensors

Postby [email protected] » Tue Dec 31, 2019 1:39 pm

Thanks again Nuke....
You seem very knowledgeable on this, would you happen to know why the speedometer is reading EXACTLY twice actual speed ?

User avatar
NukeKS14
Posts: 46
Joined: Wed Apr 10, 2019 2:50 pm
Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: RB 25DET Swap Temp Sensors

Postby NukeKS14 » Tue Dec 31, 2019 1:55 pm

Haha.... yeah seems like PO was not knowledgable about swapping the rb in.

I am at work now but tonight/ tomorrow i will post up some links for stuff to comb through. I know speedo and tachometer have to be adjusted for the swap. Ive swapped several KA drivetrains and helped friends with SR swaps. I'll get ahold of CA18det_boy and ask him if he can chime in..he has an RB swapped S14 and will be more knowledgeable on the topic.

User avatar
NukeKS14
Posts: 46
Joined: Wed Apr 10, 2019 2:50 pm
Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: RB 25DET Swap Temp Sensors

Postby NukeKS14 » Tue Dec 31, 2019 2:07 pm

Guess a follow up question that needs to be figured out is what lower harness are you using? The KA or the RB one? Not sure how to figure out other than taking pics maybe someone has an idea of what theyre looking for. KA lower harness could be causing the issue youre having w the speedo



https://zilvia.net/f/showthread.php?t=332057&page=3

Bottom of page 3 and midway down page 4. There are pictures and schematics. Were it my car, i'd pull the ecu and disconnect the body to ecu harness and have a look. If it's crimp spliced or half assed down there i would pull the harness and go through it against the wiring diagrams there and solder/heat shrink everything properly.

[email protected]
Posts: 9
Joined: Mon Dec 30, 2019 5:28 am
Car: 1994 Nissan 240sx RB 25 DET swap

Re: RB 25DET Swap Temp Sensors

Postby [email protected] » Wed Jan 01, 2020 10:02 am

I took a couple pics of wiring harness at the fan and the underhood fusebox. How do I send them in the reply ? I see a "picture" icon above the smiles, but when I select, some symbols just appear in the reply box.

User avatar
NukeKS14
Posts: 46
Joined: Wed Apr 10, 2019 2:50 pm
Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: RB 25DET Swap Temp Sensors

Postby NukeKS14 » Wed Jan 01, 2020 12:30 pm

The part you want to be looking at is in the pass kick panel behind the ecu. The lower harness is the one that connects to the transmission plugs. Its possible you have the wrong speed sensor or s.s. gear for the transmission.

[email protected]
Posts: 9
Joined: Mon Dec 30, 2019 5:28 am
Car: 1994 Nissan 240sx RB 25 DET swap

Re: RB 25DET Swap Temp Sensors

Postby [email protected] » Wed Jan 01, 2020 12:36 pm

That's what I was thinking.
I was considering putting in a gear sensor from a domestic 300ZX?


Return to “240SX Technical Forum”