Cooling Fan High Speed Relay BEC melted

[mitch]

Decided to just buy an new stock fan.
I'm guessing the original fan motor must be doing, hence, drawing to many amps.

So, replaced with a stock fan, about 85 bucks, shipped. Replaced it last week and drove the car several times since, and have not had the problem again since.

Fingers crossed, it wont happen again.

 

[olds350]

I've looked at several threads and this best describes my issue. To base line the car, I have a '08 bullitt, v8 w/ no motor mods or exhaust mods except for replacement mufflers. ~77k on the odo. So what I have is....

> AC on kicks on the low speed fan and runs the temp at ~190 constantly, no spiking
> no AC, no low speed fan, but the high speed fan kicks in around 225 on after market temp gauge. (stupid factory gauge does nothing, worthless)
> replaced fan sending unit, no change
> replaced low speed relay, no change
> no burned posts in the fuse box
> no bad fuses that I can find
> no burned wires that I can find

I smelled something on the way home from my autox last weekend, but didn't pay it much mind until the following day and the gauge started to spike at 220 while sitting in traffic on a cool morning. Normally sits at around 190 on the gauge. I can use some collective S197 wisdom here please.

Is there a separate wiring path between the fan sensor low speed and AC to activate the low speed fan?

Does the SJB have anything to do w/ this?

 

[sportinawoody]

seperate the 2 halves of the sjb under the hood, there you will find burnt terminals INSIDE the sjb. replace the fan and the sjb. problem solved until the next time it happens unless you bypass factory wiring all together

 

[mitch]

If its as bad as mine was, there is no fixing it... unless you bypasss it entirely

I had a whole new box installed.. it was expensive, but I thought it was the best option.

 

[olds350]

@ sportn and mitch. Thanks for the reply, but as noted in my previous post I have no burned, melted or bad areas in the fuse box. I have no burned wires going the fan.

To further complicate this issue, I tested the fan motor w/ a 12v source. Damn....both speeds work. There are NO melt or burn marks anywhere I can see on fan assembly.

I'm at a loss here. The only thing I haven't checked is the wire running from the fan switch under the manifold. I replaced that but didn't check the wire. Bad move on my part. So this leaves me to check the wire to the fan switch and testing the current draw on the fan motor itself. If neither of these areas have failed, then my last place to look is the PCM.

Moving on....

 

[one eyed willy]

You won't see the burnt part unless you separate the top from the Fuse/relay by removing the 4 bolts that hold the top on. Over time the fan starts pulling more amps than the wiring at the relay can handle. It heats up and melts, you get intermittent connections at that point, eventually it will just stop working.

 

[s8v4o]

I had a whole new box installed.. it was expensive, but I thought it was the best option.

In my opinion since you replaced it with what was originally there you might have the issue again later down the road. I had this problem and used a relay and a circuit breaker instead of a fuse. So far so good.

 

[sportinawoody]

i still havent seen where he stated he has actually disassembled the fuse box and looked inside. if you have DiSaSsEmBlEd the fuse box then let us know and disregard, if you haven't, THEN TEAR IT OPEN !

 

[one eyed willy]

Yeah, I'd bet money it is burnt up. A lot of people like to bump their fans down in the tune....bye bye wiring!

I bypassed mine years ago before it even had a chance to burn up, (2) 40amp relays for both high and low speeds.

 

[Saleen4971]

this makes me want to make a high-amp relay harness for mine, triggered off of OEM wiring.

especially since i want to upgrade to the gt500 fan.....

 

[olds350]

Catching up on this.... yes, I've disassembled the fuse block and there is no evidence of any over heating, no melted posts, nothing I can find.

So getting up to date, I've removed the intake manifold for a 2nd time and looked at the fan switch pigtail and checked it for continuity, all good. I've opened up the wiring split casing as much as I can and looked for burnt wires, found nothing. I've purchased a new relay and swapped it out for the low speed, high speed and PCM relays and rotated the relays w/ in the fuse box. No change.

I've looked at all the wires coming from the fuse box to the fan connector and there are no burnt wires. While the fan was out we tested and looked for any evidence of bad wires or melting. Nothing. Fan tests good on both high and low speeds.

I did some tests where the pigtail connector for the fan switch connects to the wiring harness. I used a multimeter and I'm getting ~4.5v at the connection point. From there I shorted out the the fan switch harness connector w/ a paper clip to complete the circuit.

I put my multimeter on the ground and low speed wire connector that attaches to the fan. W/ the fan switch shorted, I receive 0 volts at the fan connector.

I'm too the point of just doing the wiring reroute. Would someone be kind enough to post up how to do this reroute please? I'd appreciate a technical write up and some pics.

 

[one eyed willy]

This is probably one of the better threads about this. If it's not the BEC connections it could be a problem at the resistor box on the fan shroud, know anyone with a fan you could swap with?

I got 9 volts on low and 12 volts on high.

 

[olds350]

This is probably one of the better threads about this. If it's not the BEC connections it could be a problem at the resistor box on the fan shroud, know anyone with a fan you could swap with?

I got 9 volts on low and 12 volts on high.

I don't think testing another fan would do any good. I hooked a battery tender to the fan when it was out of the car and tested the high and low speeds, both worked fine.

I'm simply not getting any voltage at the fan connection point even w/ the fan switch connector shorted to complete the circuit.

You have to forgive my ignorance, but what is the BEC?

EDIT: I see the BEC, Bussed Electrical Center (BEC), is nothing more than the fuse box itself. Moving on....

 

[olds350]

Would someone who's done the rewire mod please post up how and what you did in regard to routing the new circuit? I'd greatly appreciate the information. I need to get my mustang back on the road asap. I have an autox this weekend and I'd rather not miss it, but I don't want to drive it w/ the low speed fan not working.

Thank you!!

 

[eighty6gt]

At least I'm running an aftermarket tune. When my car loses its marbles like Rodney's, I'll run a relay and just have the fans come on high at 190 degrees or whatever.

https://youtu.be/FLGxWPtgodo

 

[olds350]

Taking the advice that I could short the 30/87 posts, I have some updated news. When I shorted the 30/87 terminals on the low speed relay, success! I had power at the fan connection. When I shorted the 30/87 terminals on the PCM relay, I had some interesting clicking, no voltage at the fan connection and the message area for the trip mileage and the odo stated a charging system error. I removed the jumper, turned the key off and then started the car. The message displayed correctly.

So what does that mean, aside from the fact I still have an issue. What is this pointing to?

@ eighty6gt, thanks for the rapp'n Rodney link, good one . That car is showing me no respect right now....

 

[olds350]

based on some additional advice, I removed the low speed relay and then tested voltage to terminal 86 on the fuse box. I did see 12v via the volt meter on 86. My other sources are telling me if I receive power at 86 and if jumping 30/87 gets me power at the fan connection, then I have issue w/ the ECU/PCM itself. I'm about to pull the ECU and look inside for any damage.

 

[eighty6gt]

Either with the ecu or the wiring to the trigger on that relay you're fumbling around with. Why not backprobe and node the ecu output? Leave the fan unhooked, watch the temps, and as they go past low and high speed triggers you should see the lights come on.

 

[olds350]

OK, I'm about to close in on this freaking problem. Took the mustang over to my trusted BMW mechanic and had him hook the car up to his computer and he also looked at AllData. So, here's what we did.

> putting the volt meter on terminal 85 w/ the relay in showed 12v on the meter.
> hard ground of terminal 85 w/ the relay in place caused the low speed fan to turn on.
> ran a self check of the cooling system. I think most of that worked, but the fan only came on once.

From there we found the pin out on the PCM. So once I remove the lower 70 pin connector form the PCM, I need to check the continuity of the following...

> pin 7 to terminal 85 of the low speed relay. That's the info out path for the PCM and will tell me if the wire is good.
> pin 41 back to fan switch. That's the info in path to the PCM. Again checking for a bad wire.

If the continuity on both of those wires is good, then the only thing bad is the PCM itself and I get to spend a crap ton of money. Will know later this evening once the car cools down and I get a chance to touch it.

 

[olds350]

well damn.... continuity checks out good. Looks like I'm spending some money...