Buick Roadmaster Drivers Side Fan Not Coming On.

[loganlanguet]

Hello,

I recently purchased a 1994 Buick Roadmaster sedan. I was driving around and the tempature got much higher than usual. One tick below the red. Ive read a bit about how one fan doesn't activate till around 230 degrees. However both should come on when the AC is turned on. So I started the car, and turned the AC on. The drivers side fan wouldnt turn on. The fuses from what I could see looked fine. I'm not quite sure if that side is the primary, or secondary fan. I'm going to be driving from Maine to Flordia, and I want to make sure the cooling system is in check before doing so.

Thanks!

 

[RD_Atlanta]

Have you checked to see if 12v is reaching the driver's side fan motor?

 

[loganlanguet]

Have you checked to see if 12v is reaching the driver's side fan motor?

To be 100% honest, I'm not quite sure how to test for that on this car. Ive had it for two weeks 😆

 

[RD_Atlanta]

To be 100% honest, I'm not quite sure how to test for that on this car. Ive had it for two weeks 😆

There 's two modes for the fans, high speed and low speed. In HS, both fans get 12-14v and in low speed, each fan gets 6-7v because they are wired in series. If the drivers side fan has an open circuit, neither will run but when the air is on, both run at H.S.
1. Disconnect the driver's side fan & connect a volt meter to the driver's side fan then start the car with the air on. With the passenger side fan running, you should see 12-14 volts at the driver's side fan connector (across both wires).

All evidence points toward a bad driver's side fan but this quick test will prove if that's the case.

These fans are available in bone yards.

 

[loganlanguet]

There 's two modes for the fans, high speed and low speed. In HS, both fans get 12-14v and in low speed, each fan gets 6-7v because they are wired in series. If the drivers side fan has an open circuit, neither will run but when the air is on, both run at H.S.
1. Disconnect the driver's side fan & connect a volt meter to the driver's side fan then start the car with the air on. With the passenger side fan running, you should see 12-14 volts at the driver's side fan connector (across both wires).

All evidence points toward a bad driver's side fan but this quick test will prove if that's the case.

These fans are available in bone yards.

I will check that!

 

[RD_Atlanta]

I was out hiking when I sent that last post. For some reason, I thought that you have a Buick LeSabre. On the 1994 Buick Roadmaster, there may not be a low speed and high speed mode. But regardless, the test should work still work fine, with the air on if your getting 12-14v to the driver's side fan and the fan is not running, you have a fan with an open circuit. These fans are available new. Link

 

[loganlanguet]

I checked the fuses. Going to check the relay today and try and swap the one thats working to the one that isn't to see if thats the issue. I have to purchase a multimeter in order to test if the fan is infact getting voltage. So I'm gonna go simple first. This is what is happening, the AC was on. Passenger spins, drivers side doesn't. From what I've read in other threads, the passenger side is the one that commonly fails. It has a replacement set of fans in there. The date was I believe 2005.

 

[RD_Atlanta]

I checked the fuses. Going to check the relay today and try and swap the one thats working to the one that isn't to see if thats the issue. I have to purchase a multimeter in order to test if the fan is infact getting voltage. So I'm gonna go simple first. This is what is happening, the AC was on. Passenger spins, drivers side doesn't. From what I've read in other threads, the passenger side is the one that commonly fails. It has a replacement set of fans in there. The date was I believe 2005.

You can get a digital meter for about $14 on Amazon that will be fine small jobs like this...

https://www.amazon.com/AstroAI-Digital-Multimeter-Voltage-Tester/dp/B01ISAMUA6/ref=mp_s_a_1_3_maf_2?adgrpid=156516933981&dib=eyJ2IjoiMSJ9.eeEfLUxoX8T_oHzD0-ckp7xFckindY3y4fd_sIsyHTPLiuLZzRT79aX7DG5F1yXmch7boycgM8oFG_ooZi73kflKolMPK1tVe9l6Gsj3yi5mLlgEmM-hyGiiZYw5V4BwswStN8nwH_Y7_x-Gz3t7MhjQa_A1SZZE0nfq87_3n7ODX_IrfJfLfyQobeBomHCa6jnNF9mPYlPSFbuJezCGWA.szGTmS3_1kBH7OX19Ilv3c3zZxkBrgC66PPYHlUzMUg&dib_tag=se&hvadid=693002612078&hvdev=m&hvexpln=68&hvlocphy=9010769&hvnetw=g&hvocijid=12154789674252489565--&hvqmt=e&hvrand=12154789674252489565&hvtargid=kwd-839615232947&hydadcr=24173_13541861&keywords=amazon+digital+voltmeter&mcid=ef02efc560ed3ed18ffaf83aaa421706&qid=1758034040&sr=8-3

 

[loganlanguet]

Good news bad news, good news, I did some research. And it said that if you disconnect the tempature sensor from the water pump the fan will come on. I did that and it in fact did come on. Bad news, it still will not turn on when the water pump sensor is plugged back in. So it isn't the relays, it isn't the fuses, and it isn't the motor. From what I read it could in fact be the tempature sensor itself. Or the PCM.

 

[loganlanguet]

I also plugged back in the tempature sensor and let the car run. It got to 240 degrees and the fan that works came on. So it is the primary fan that isn't operating.

 

[HotZ28]

Have you even considered replacing the thermostat? It sounds like it failed closed!

 

[Riskit]

I’m new to this car and the LT1, but cars Im not… Im having the same issue going on and just saw this post. You learned the temp sensor at the water pump and how it’s great to check the fans working easily. There is an other temp sensor on the pass side head just above the spark plug between the 6-8 plug. Next issue is getting the sensor for that.. they are not the same. The one at the water pump is a standard 2 wire and the one on the head is an odd plug.. I also think the sensor might be specific for a car with only an idiot light, gauge or digital dash.. not sure on that 100%..
USE MY INPUT AS ONLY ideas to make you think… Id love to see someone tell me/you exactly how to fix this issue.

at head;



At water pump



There is more to this issue then just these sensors.. it obviously could be the PCM.. it could also be a bad ground. The ground wire is a blue wire and a green wire. The primary fan (fan 1) is the passenger fan, secondary (fan2) is drivers side. If you turn on ac only the (fan1) comes on.

Next, someone above talked about the fans running in series.. the way the fans are triggered from the PCM is through NEG not positive. The PCM sends a ground trigger (this was to help the relay and constant power safety)

Also, if your coolant is low… the sensor in the head will never trigger and the PCM will never turn the fans on.

You can do a YouTube search for LT1 and fans and you will see Camaro guys have been dealing with this for years. Most people end up adding a toggle switch and calling it a day.
I would like to have my car fun as factory planned so I have these sensors on order and 🙏🏻 this solves the issue. If I end up finding it’s the PCM then I’ll add a switch in the car.
You say you’re taking a trip.. if in a bind you can just unplug the switch at the water pump.

PLEASE REMEMBER I AM NEW TO THIS MOTOR AND COULD BE WRONG…

 

[Riskit]

And maybe you could use this

 

[Riskit]

Diagrams

 

[loganlanguet]

So I did some voltage testing yesterday. And there is no power to that fans fuse, nor the relay.

 

[loganlanguet]

Have you even considered replacing the thermostat? It sounds like it failed closed!

I have no experience with these cars. But if it was the thermostat how could I test it? And where is it located?

 

[loganlanguet]

For now I have a closed relay installed, and I plug it in when I want to drive. And unplug it when I shut the car off. Not a perminate fix by any means, but its the next best thing for now.

 

[loganlanguet]

So I did some voltage testing yesterday. And there is no power to that fans fuse, nor the relay.

Every other fuse and relay gets the proper voltage.

 

[RD_Atlanta]

So I did some voltage testing yesterday. And there is no power to that fans fuse, nor the relay.

You mentioned that the passenger side fan energizes at about 230 degrees. F. Do you recall at what temperature the driver's side fan used to energize when it worked?

Do you have a wiring diagram of the fan control circuit for your 1994 that you can attach here for all of us to look at?

The reason I ask is many of the OBDII GMs control the fans from the BCM (or a similar module outside the PCM) by default. In the case of the V6 fwd P04 PCMs (which I have), the control can be easily switched to the PCM, which I do in all of my PCMs. This is significant because GM (by default) sets the fans to energize at an extremely high temperature, which most of us do not agree with. Once I tell the PCM to take control, I can set the fans to come on at a temperature that (I think) is far more reasonable for the engine & transmission longevity. And the temperature to switch off.

I'm not sure what is in control of your fans on a 1994. Many 1994 & 95 GMs went through an interim OBD period often referred to as OBD 1.5, which was pre-OBDII and introduced the BCM.

If you could post a fan-control wiring diagram, many of us in the forum could contribute more.

 

[loganlanguet]

Earlier in this post, a member posted this diagram, which is the correct diagram for my car.