GTO Fan Relay How-To: Part 2

Hopefully, you already read the details of how I found out my GTO had an overheating problem. If not, here it is.

GTO Fan Relay How-To: Part 1

Up to date yet?

Okay, let’s move on. After letting the car sit for a few days I figured it was about time to see what was going on. While the car had been sitting there hadn’t been any leaks, which was a good sign. I confirmed this by checking the levels in both the radiator and the overflow tank. Both were as I had left them and at their appropriate levels, so I was able to cross them off my list. Next up I started her up and let her run. At first I switched on the A/C to see if the fans would cycle on. Sure enough, they didn’t. Regardless though I let her run until she reached operating temperature. With the fans clearly not running I shut her off knowing that at least one of the problems was the fans.

Diagnosing an electrical fan issue isn’t as simple as throwing a new fan in and calling it a day. Given that they are electric fans it is important to check the wiring and sensors, as well as the fan motor itself before throwing good money at working parts. I’ve found that the easiest way to start diagnosing the issue is to manually turn the fans on. This practice is helpful regardless of what type or model car you’re working on. To do this you’ll need to locate the fan relay within the relay/fuse box. It’s is important to note that this is not the same fuse box that you’ll typically find within the car. That fuse box houses smaller fuses for the car’s more specific systems. The relay/fuse box, on the other hand, is usually in the engine compartment and houses the relays for the individual electrical system, as well as the heavier duty fuses for the main electrical lines. In the GTO it is found adjacent to the passenger side front fender right above the wheel well. Once you open her up you’ll see that each of the relays and fuses is clearly marked.

After locating the fan relays (the GTO has 3), you’ll want to pop the main relay off and jump it. Now, this is where things will get a little goofy. The GTO, and I assume that this is because it is made in Australia, uses non-standard relays. A normal relay’s internal wiring will go from “87”, “85”, “30” & “86”, in a clockwise pattern starting at the top. However the GTO’s goes from “87”, “85”, “86” & “30”. As you can see the “30” & “86” terminals are swapped. At first glance the difference does not seem significant, but they are and we’ll see why later. In the meantime though, let’s go ahead and check the fans. You’ll want to connect the relay terminal that corresponds to “30”, with the terminal that corresponds to “87”. What this is doing is allowing the electricity to flow from the battery directly to the fans. This mimics the function of the computer turning on the relay by powering the “86” terminal. While that truly sounds more complicated than what it is, trust me it’s straightforward. Imagine “30” as one side of a river and “87” as the other side. The bridge connecting both sides is constantly raised. In order to close it and allow traffic to pass the bridge operator, let’s call him Mr. “86”, must be notified. If the bridge isn’t closing though you’ll need to manually close it, connecting “30” and “87”. This is exactly what you’re going to do. It’ll just be done with a piece of wire.

To jump the relay you can literally just use a piece of insulated electrical wire (might crackle a bit but that’s fine). Or you can use the testing leads from a voltmeter. The latter is my preferred method as the leads have a pointy tip which fit within the terminals quite nicely. As I pushed the leads into the respective terminal I was very satisfied to hear the fans spring to life. Thus confirming that the fan motors are functioning correctly.

At this point, I’ve crossed a number of potential culprits off my list. I know that the radiator and overflow tank are fine. There’s no leak emanating from below the car so the water pump is in good shape, and the fans turn on when manually connected so they are working as well. That leaves me with a potential electrical issue which can be boiled down to two things. One, the computer isn’t sending the signal to the relay (i.e. our bridge operator, Mr. “86”, is not getting notified). Or, two, the relay itself is damaged. Since I already had the engine bay open testing the signal to the relay was the easier of the two to check.

To check that the signal is reaching the relay you’ll need a voltmeter or a test light. Using either tool you’ll first want to connect the negative (or black) side to a solid ground. This can be a bolt on the car’s chassis, the engine itself, or the negative terminal of the battery. Doesn’t really matter either way, but most people will tell you to use a chassis ground (less moving parts and electrical current, probably safer too). Then you’ll want to connect the positive side to Mr. “86”. With the positive side or test light connected to “86”, once the car hits its normal operating temperature you should see 12 volts emanating from that terminal. Or in the case of the test light, the light should turn on. This is the car’s way of signaling that the fans should come on. Sure enough, the GTO was sending the signal, so that seemed to be working correctly as well.

With the engine sending the signal to turn the fans on, and the fans actually working, all signs seem to be pointing to a faulty relay. With this in mind, I grabbed an extra set of relays I had laying around and threw them in. Cranked the car over and let her idle. As the operating temperatures began to rise I was waiting for the fans to cycle on… and I kept waiting. They never turned on. Okay, maybe the extra set of relays I had were faulty as well. No problem. I went to an Autozone that’s a few blocks away and purchased a new set. Threw those in, started up the GTO, and waited for the fans to turn on… and I kept on waiting. No fans…

At this point I’m starting to get a bit perplexed. Maybe the original relays weren’t bad at all and it’s something else entirely. So I went ahead and tested the relays manually. To manually test a relay you’ll first need to remove it from the car. Then you’ll have to take the protective housing off. This can be done with a small flathead screwdriver by popping off the clips on the side. Once you have the internal mechanisms exposed you’ll need to locate the bridge. This is the metal portion that moves when the relay is activated. Using a voltmeter you’ll want to check the resistance between “30” and “87”. With each lead of the voltmeter touching one of the terminals, you’ll want to manually close the bridge. This should cause a change in the resistance as “30” and “87” are now connected. This is, of course, assuming the relay is working. If you do not see a fluctuation in the resistance then the relay is more likely damaged. Following this procedure, I went ahead and tested the original GTO relays, and sure enough, they all seemed to work.

I am now beyond perplexed and downright frustrated with the car. By all indications, it should be working correctly. With no clear direction or culprit, I did what I always do, reached out to the forums and see if anyone has any ideas. After scouring the GTO forum for a bit (www.ls2gto.com is THE source for GTO information btw), I had realized two things. One, GTO relays are very temperamental, so they may appear to be working normally but once actually put to the task the higher voltage of the system causes them to malfunction. More importantly, though, GTO relays are NON-STANDARD! Remember I mentioned this earlier. As such those new relays I had bought were useless. With the “86” & “30” terminals being swapped, there was no possible way for it to work. In fact, I’m lucky they didn’t screw anything up. So the best way to make sure that the culprit wasn’t the relays was to order a new set. Unfortunately, you can’t get GTO relays at your local autopart. Even finding them on Amazon seemed less than confidence inspiring. I ended up getting them through www.rockauto.com, and they weren’t cheap. Don’t get me wrong, they didn’t break the bank. I think the total was $45 give or take, but that’s a lot of money for 3 relays… The part numbers in question for the relays are as follows:

• Low speed fan relay (Main, you need one) GM #92092445
• High speed fan relay (Secondary, you need two) GM #92092444

What are you going to do though?

A week later my relays arrived. I popped them in, started the car and was greeted with the reassuring sound of electrical fans blasting heat away from the radiator. Problem solved, but wow was that annoying. The intricacies of driving a limited production car manufactured in a country that doesn’t typically export cars to the United States makes any repair on a GTO unique, to say the least. All I know is I can really do without another overheating car at this point.

Useful Parts & Tools to Help you with this DIY Project: