Nissan Forum banner

1 - 4 of 4 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #1
My wife's car is a 96 Sentra with the GA16DE and an automatic transmission. Over the summer on really hot days the transmission would have trouble shifting. I always assumed it was something AT related but after changing the AT fluid and filter, it continued to do it. So I looked into the cooling system because it was strange how it was only on hot days. I changed the coolant in the radiator and in the process, I noticed the cooling fans weren't on when they should have been.

So I checked the relay, the temperature sensor, and continuity throughout the system and found no problems. I've tried putting the AC and blower on which doesn't turn the fans on. I've put a 150 ohm resistor on the coolant temperature sensor which also didn't turn on the fans. I know the fans work because I can take a piece of wire and bridge the relay harness and they both come on.

The one thing I did find out is that the ECU is not sending any signal to the relay. When the ignition is on, there is 13+ Volts on two of terminals on the relay harness. There is also continuity between one of the terminals and ground. Then the other terminal is the one that is connected to the ECU which I tested for continuity and was good. However, the voltage at the terminal in the relay harness never changes (well, fluctuates in mV - but never gets about 100mV). So why is the ECU not telling the fans to turn on?

Anyone have any ideas? Am I looking in the right direction? Could it be something else? I don't think the ECU is bad because the car runs fine otherwise. The ECU also only throws the code 0505, which is No Failure Detected.

Thanks in advance.
 

·
Registered
2018 Nissan Pathfinder SL
Joined
·
4,237 Posts
Well you seem to have ruled out everything but the ECU.
Just because it isn't detecting an error doesn't mean its not got a bad output driver.
So as I see it your options are
1) try another ECU
2) Forget the ECU and wire up a relay using the A/c power AND a temp sensor on the radiator or hose, and i mean you can use the stock one since its good.
 

·
Registered
Joined
·
2 Posts
Discussion Starter #3
Well, I did finally get it working. After pulling the ECU connector on and off a bunch of times, it started working again. I also replaced the relay on the ECU, even though it test ed fine. I think it must have not been making a good connection at the ECU, because the continuity in the harness was fine, so pulling the connector on and off must have cleaned it off enough to make a connection again.

I was about to wire up a switch inside the car before it started working again. Your idea of wiring it up to the stock temp sensor sounds like a much better idea though. If it happens again, that's probably the way I'll go.

Thanks for your help.
 

·
Registered
Joined
·
11 Posts
I went through this and it was the ECU, but was probably the fans at first, since they were both bad. I have no proof, but I think the guy I got the car from blew the output transistor in the ECU while tracing the problem, shorting the wrong pins in the relay connector could have done it and he may have done that by mistake.
 
1 - 4 of 4 Posts
Top