radiator fan keeps running till battery dies
- Thread starter oldskool
- Start date
It's very likely to be your fan control unit. This a symptom of a failure in that unit.
Part number is 37735-PR7-A01
Part number is 37735-PR7-A01
Honcho's answer is correct / incorrect depending on the circumstances of your problem. If the ignition key is switched to the run position and the radiator fan is running with a cold engine, then he is likely correct that the Fan control unit is the problem; but, a failed temperature sensor could also be the problem. Be aware that the fan unit suffers the same problems as the other NSX electronics (solder cracks and I believe capacitor issues). If you diagnose the fan unit being the problem then pull it apart and examine it and it may be repairable.
Because you said that the fan is running until the battery is dead, I take it that the radiator fan is running even when the ignition is switched off. If so, then I respectfully submit that Honcho might be incorrect. This is the wiring diagram for the fan control
The radiator fan itself is supplied off of un switched power. However, both the fan control unit and the fan high and low relays are supplied from switched power. Unless your vehicle has had botched wiring surgery, there is no way that the fan control unit can power up either of the two relays to switch the fan on when the ignition switch is off. If your fan is running when the ignition is switched off, then you have one of three problems:
1) you have a short to ground somewhere on the wht/blu wire coming off the fan motor. This could include a melted fan relay socket which is allowing a ground short
2) the high or low fan relay internal contacts have welded themselves shut
3) the fan relay overheated and has melted the socket which is allowing a short to ground on the wht/blu wire.
You said you checked the relays. How did you check the relays and did you check the right ones? From year to year Honda moved the relays around. If you used a 1991 service manual to determine relay location it shows both fan relays are in relay box A. As of 1997, the high relay switched positions with the horn relay in box A and the low relay moved to box B.
Because you said that the fan is running until the battery is dead, I take it that the radiator fan is running even when the ignition is switched off. If so, then I respectfully submit that Honcho might be incorrect. This is the wiring diagram for the fan control
The radiator fan itself is supplied off of un switched power. However, both the fan control unit and the fan high and low relays are supplied from switched power. Unless your vehicle has had botched wiring surgery, there is no way that the fan control unit can power up either of the two relays to switch the fan on when the ignition switch is off. If your fan is running when the ignition is switched off, then you have one of three problems:
1) you have a short to ground somewhere on the wht/blu wire coming off the fan motor. This could include a melted fan relay socket which is allowing a ground short
2) the high or low fan relay internal contacts have welded themselves shut
3) the fan relay overheated and has melted the socket which is allowing a short to ground on the wht/blu wire.
You said you checked the relays. How did you check the relays and did you check the right ones? From year to year Honda moved the relays around. If you used a 1991 service manual to determine relay location it shows both fan relays are in relay box A. As of 1997, the high relay switched positions with the horn relay in box A and the low relay moved to box B.
thanks for the info, yes when the key was out the fan kept running till it was dead. I used to have a 91 prelude that would do that but it turned itself off. Thus I thought that was the same process as the honda. I checked the fuse box and it said fan relay on there.
Ah ok, then @Old Guy is right. You either have a short in the wires or in the relays.
I assume you mean relay box because there are no fuses in the box that holds the high and low radiator fan relays. You must have an early car because the later cars have no labels on the relay box lids. On the later cars you need the service manual or the Electrical Trouble Shooting manual to determine which relay is which. If the fan is running because of a stuck relay, you can pull the high relay out and then the low relay out. The fan should stop running when the problem relay is removed - if the problem is the relay.
First off, make sure that A and B relay case lids have not been interchanged and you are checking the wrong relays. On my 2000, the lids look identical; but, are not interchangeable because of some webbing added under one to the lids. I don't know whether early cars also have this non interchangeable feature.
Since your join date was 2022 October, does that mean you are a relatively new owner? If so, has the rad fan run like this since you got it? If the rad fan has been doing this since day 1 you have a serious non stock wiring screw-up of some kind because with the OEM wiring / control arrangement it is impossible for the rad fan to run with the relays removed. Is there a chance that a previous owner got creative with some wiring, perhaps if the fan control unit crapped out?
If this fan running problem is a recent development I would check the base of the high and low relay sockets looking for melted plastic. You may have to detach the relay box from the firewall so that you can look underneath to check for damage. What you are looking for is melting that would have allowed the terminal with the black wire to move and come into contact with the blue white wire (or vice versa).
Since I am now at the point of flinging cooked spaghetti at the wall to see what sticks, if you have a continuity tester do a check from the white blue wire right at the rad fan motor to the terminals in the relay box for the high and low relays that connect to the white / blue wire If there is no continuity then the rad fan is going some other place.
Since your join date was 2022 October, does that mean you are a relatively new owner? If so, has the rad fan run like this since you got it? If the rad fan has been doing this since day 1 you have a serious non stock wiring screw-up of some kind because with the OEM wiring / control arrangement it is impossible for the rad fan to run with the relays removed. Is there a chance that a previous owner got creative with some wiring, perhaps if the fan control unit crapped out?
If this fan running problem is a recent development I would check the base of the high and low relay sockets looking for melted plastic. You may have to detach the relay box from the firewall so that you can look underneath to check for damage. What you are looking for is melting that would have allowed the terminal with the black wire to move and come into contact with the blue white wire (or vice versa).
Since I am now at the point of flinging cooked spaghetti at the wall to see what sticks, if you have a continuity tester do a check from the white blue wire right at the rad fan motor to the terminals in the relay box for the high and low relays that connect to the white / blue wire If there is no continuity then the rad fan is going some other place.
Great feedback prime team! You guys rock.
Yes I'm a new owner of a 1997 NSX-T, well I did get the AC fixed at a local shop and they did some wiring in the relay case. I don't know if it was A or B, however it was the RT of the fuse box. Every thing was fine till recently with the radiator fan kept running. I'll check for the continuity of the fan.
