Electric Radiator Fans Randomly Turning On When Ignition Is Off

[JJ3373]

Hello, everyone! New to the forum, so I hope this is in the right section.

I have a 2006 suburban with the dual electric radiator fans. After leaving the truck off for a random amount of time, the radiator fans will turn on, draining the battery. I've replaced the coolant sensor, and will be replacing the relays next, but they seem OK. If I yank out fan relay 1 or 3, or the 40 amp fuse, the fans stop.

Interestingly enough, with key in accessory mode, the radiator fans stop.

Anyone have any ideas?

 

[Marky Dissod]

Some kind of odd wiring issue?

 

[Tonimus]

First, welcome to the forum! Let's see some pics of the rig!

Second, we need to know year and model to help the best.

 

[ORVietVet]

Yes, welcome to the forum from Oregon.

@Tonimus, the OP said "2006 suburban". @JJ3373, do a Signature with all the vehicle(s) info.

 

[ORVietVet]

Yes, welcome to the forum from Oregon.

@Tonimus, the OP said "2006 suburban". @JJ3373, do a Signature with all the vehicle(s) info.

 

[ORVietVet]

I have no idea why this "finecky" site posted that 2 times.

 

[Cadillacmak]

Hello, everyone! New to the forum, so I hope this is in the right section.

I have a 2006 suburban with the dual electric radiator fans. After leaving the truck off for a random amount of time, the radiator fans will turn on, draining the battery. I've replaced the coolant sensor, and will be replacing the relays next, but they seem OK. If I yank out fan relay 1 or 3, or the 40 amp fuse, the fans stop.

Interestingly enough, with key in accessory mode, the radiator fans stop.

Anyone have any ideas?

My dad had a Cadillac that would do that randomly in the middle of the night. Someone correct me if I am wrong, but its a module or the PMC that signals the relay after it gets info from sensors and the module is at fault.

 

[JJ3373]

My dad had a Cadillac that would do that randomly in the middle of the night. Someone correct me if I am wrong, but its a module or the PMC that signals the relay after it gets info from sensors and the module is at fault.

It's looking like the PCM at the moment! Today the fans were stuck on with ignition off, even with 3 new relays.

I disconnected the PCM and some of the pins were crusty, including the coolant temp sensor pin. Also, probing the fan signal wires that connect to the PCM show no shorts, so the wiring should be good.

One of the pin actually broke off and got stuck in the PCM connector, so I'll be getting a new PCM anyway. If you know how to get a broken pin out of a PCM connector, let me know!

I blasted the remaining pins with contact cleaner and a brush, and the fans haven't kicked on... yet. So hopefully a new PCM will do the trick.

 

[Cadillacmak]

If you know how to get a broken pin out of a PCM connector, let me know!

I haven't had to do that yet! Sounds like a pain.

 

[JJ3373]

Well, fans kicked back on. Next thing is to get that PCM.

Supposedly, it's had a 6.0 put in in the past, but is there anyway to confirm that, before I get the new PCM?

 

[Tonimus]

Yes, welcome to the forum from Oregon.

@Tonimus, the OP said "2006 suburban". @JJ3373, do a Signature with all the vehicle(s) info.

Not sure how I missed that.

It's looking like the PCM at the moment! Today the fans were stuck on with ignition off, even with 3 new relays.

I disconnected the PCM and some of the pins were crusty, including the coolant temp sensor pin. Also, probing the fan signal wires that connect to the PCM show no shorts, so the wiring should be good.

One of the pin actually broke off and got stuck in the PCM connector, so I'll be getting a new PCM anyway. If you know how to get a broken pin out of a PCM connector, let me know!

I blasted the remaining pins with contact cleaner and a brush, and the fans haven't kicked on... yet. So hopefully a new PCM will do the trick.

To get the pin out of the harness plug, the back of the connector comes off and you pull the front colored plastic part. You'll see a small retaining tab holding the pin in. Pops right out.

The 8th digit of the vin will tell you what engine it had originally. There should also be a vin or partial vin on the block. I believe at the rear of the block under the driver's side cylinder head. Might also have 6.0 cast into the block on the front side, just to the right of the timing cover, below the head.

Was that PCM jammed full of dielectric grease?

 

[JJ3373]

Not sure how I missed that.


To get the pin out of the harness plug, the back of the connector comes off and you pull the front colored plastic part. You'll see a small retaining tab holding the pin in. Pops right out.

The 8th digit of the vin will tell you what engine it had originally. There should also be a vin or partial vin on the block. I believe at the rear of the block under the driver's side cylinder head. Might also have 6.0 cast into the block on the front side, just to the right of the timing cover, below the head.

Was that PCM jammed full of dielectric grease?

Awesome, sounds easy enough.

Yep, I know originally it had a 5.3 in it, according to the VIN. When I bought it, the guy said there was a 6.0L in it. I didn't care, since I don't mind either engine, but I'd rather verify before getting the new PCM, so the tune is right. Are any of those markings visible with the engine still in place?

The connector might have some grease in there at some point, but it mostly looked like water.

 

[Tonimus]

All the markings I noted might be visible in place. Just a matter of doing the right yoga.

With an $80 OBD scanner https://obdxpro.com/product/obdx-pro-vx-obd2-diagnostics-and-tuning/ and a little computer usage, it would be easy to copy your tune to a new PCM.

 

[JJ3373]

All the markings I noted might be visible in place. Just a matter of doing the right yoga.

With an $80 OBD scanner https://obdxpro.com/product/obdx-pro-vx-obd2-diagnostics-and-tuning/ and a little computer usage, it would be easy to copy your tune to a new PCM.

Perfect! I'll investigate both.

 

[JJ3373]

Just a little update: it was indeed the PCM. Got that sorted and now it's working good.

 

[Cadillacmak]

Just a little update: it was indeed the PCM. Got that sorted and now it's working good.

Glad you got it worked out and thank you for the update!

 

[AuroraGirl]

the behavior is expected and normal if you were in a newer or higher end vehicle that year


Afterblow is where the fans come on after shut down to dry off the evaporator so it doesnt grow bacteria and fungus

 

[Marky Dissod]

In case it helps anyone, I've confirmed that my HVAC both purges and afterblows.

 

[AuroraGirl]

In case it helps anyone, I've confirmed that my HVAC both purges and afterblows.

You have to use an add on kit to add the feature of afterblow to gmt800

 

[Marky Dissod]

In case it helps anyone, I've confirmed that my HVAC both purges and afterblows.

You have to use an add on kit to add the feature of afterblow to a gmt800

Meaning that a previous owner did so. Guess I'm wondering how it was done, and why? But I'm very grateful for their presence.