Cooling fan will not turn off

[davidr]

have a 2006 Tahoe Z71.

Here is what I am dealing with.

Knock sensor codes came up a month ago. I reset the codes. They started to come up more frequently. I also had a code pop that was something about a open circuit. The dealer said it was related to the onstar antenna but not important if I do not use onstar.

Yesterday I noticed that the cooling fans were running (it was 30 degrees outside and the truck was at normal temps (gauge read ok as we'll as confirmed via autocal scanner)

I let them run for about 30 minutes just in case (car off, keys out). They kept running. I then disconnected the negative terminal from the battery to have them stop. I reconnected the terminal after a few minutes because I wanted to see if the fans would still run. THEY DID NOT. Well, I went back into the house.

Now, go out this morning and the fans are running again! They turned back on overnight at some point. No one used the vehicle or started it or anything else. I did also go out and check before I went to bed and the fans were not running.

I read on another forum something about fan wires, ignition or injector wires and knock sensor wires all being contained in one harness. Sometimes that harness corrodes, melts or comes loose. The post also said something about the codes for knock sensors, misfire cylinder history and the fan issues are a symptom of this problem or the harness.

So, where is that harness and what are the colors to check, etc? I am also going to replace the fan relays to test (once I recharge the battery....)

UPDATE =============
OK. So, I have 3 relays in the relay housing for the fans. 2 are grey 4 prongs and the other is a black 5 prong.

I pulled the grey one in the center and the fans cut off (Cooling Fan 1 relay). I then pulled the other grey one (Cooling Fan 2) and put it in to where the other was just pulled and the fans started up again.

I pull the Cooling Fan 3 relay and it all shuts off as well.

Looks like it is getting a call for switch from somewhere. I JUST replaced the Coolant Temp Sensor 2 weeks back.

I did buy all new relays and install all 3, same exact results. So, seems not the relays stuck, etc..

I also let the truck cool. I put the relays in and the fans cut on. I then pulled the wire from the coolant temp sensor (which should shut off the fans based on what I read). It did not turn off the fans.

So, not sure where to go at this point.

Thanks again
David

 

[Blacked-out-Tahoe]

If your knock sensor codes are popping up with circuit codes you need to replace both sensors and the knock sensor harness. They sit in the valley and get filled with dirt and water and set codes. My #2 was full of water. Start with that because it goes into limp mode. If that doesn't fix it I would check the fans themselves. Sounds like the fans are bad they can short out and stay on when they go bad. Hope that helps

 

[kses123]

I hope to find out what this issue is.

 

[davidr]

If your knock sensor codes are popping up with circuit codes you need to replace both sensors and the knock sensor harness. They sit in the valley and get filled with dirt and water and set codes. My #2 was full of water. Start with that because it goes into limp mode. If that doesn't fix it I would check the fans themselves. Sounds like the fans are bad they can short out and stay on when they go bad. Hope that helps

How do you check the fans are shorted out? I am curious since it is BOTH fans running but possible.

 

[Blacked-out-Tahoe]

You can check resistance in the fan motors. They should be wired together so they both turn on at the same time and when the motor shorts out it can short to power on all the time or not work at all. And can make both fans power up if one of them is bad. I would also check for TSB's related to fan motors and see if there is anything

 

[davidr]

Updates

UPDATES:

- Replaced all 3 relays. I tested the old relays and all seemed ok. I tested the new relays before installing, all tested good.
- Turned on the car, same results.
- I pulled the connections to the PCM and checked for burnt runs, etc. Nothing with visual inspection. I did hit them with contact cleaner before I plugged them back in.
- I pulled the wires off the ECT while truck was running. Fans continued to run. Truck threw a P0118 fault, as expected. I reset that code.
- I disconnected the large harness beside the relay housing and checked all connections visually. I hit them with contact cleaner and reinstalled.
- I pulled the ground strap at the firewall and cleaned the connection.
- Truck is NOT overheating (I replaced the radiator, thermostat and all hoses about 3 months ago)


OBSERVATIONS:
- Fans run on HIGH when car is running.
- Fans run on LOW when car is shut down.
- If I disconnect battery and reconnect, the fans shut off until I restart the vehicle. Then they turn on and back to aggrevating me.
- If I pull relay to "COOL FAN 1" both fans stop. If I plug it back in, they start back up.
- If I pull relay to "COOL FAN 2", there is no change.
- If I pull relay to "COOL FAN 3", both fans stop.
- If I disconnect the wires to the fans themselves, they obviously stop.
- Here is where it gets interesting...If I disconnect the wires to one specific fan, the fans stop. The wires I pulled are to the fan on the driver side (Black and Blue) wires.

For now, I am keeping the plug to the fan (black and blue wire set) unplugged so I can drive and not drain battery. It is cold enough and the fans don't run much in the winter, if ever.



Any ideas?

 

[Rivieraracing]

I see that you replaced the coolant temp switch a couple weeks ago, what was the old one doing for you to replace it and what brand of switch did you go with? OEM? If not oem, which store did you buy from? What does your temp gauge do now with the new one?

If both fans are being told to kick on and you have replaced the relays with known good ones, then you have a short in a wire somewhere (also how do the relay socket plugs look? Any melted slightly?) or something is telling the computer that your truck is too warm and needs to have the fans on

 

[davidr]

I see that you replaced the coolant temp switch a couple weeks ago, what was the old one doing for you to replace it and what brand of switch did you go with? OEM? If not oem, which store did you buy from? What does your temp gauge do now with the new one?

If both fans are being told to kick on and you have replaced the relays with known good ones, then you either have a short in a wire somewhere (also how do the relay socket plugs look? Any melted slightly?) or something is telling the computer that your truck is too warm and needs to have the fans on (maybe that new coolant switch)!

To be more specific, I replaced the old ECT with a new ECT. I replaced it since the old one had a high resistance. I replaced it because the dealership said it should be replaced when I replace the radiator due to age and mileage, etc. I replaced it with an OEM part. Everything has worked fine until last week. I replaced it on 12/08/12, so about 2 1/2 months or so.

As I have read (not sure if it is fact), if you pull the connection off the ECT, the fans should stop working since it opens the circuit and there is no call to the PCM to start the fans. Not sure this is correct but was one troubleshooting step I have read on many sites that I should try. Can you confirm? Is there another specific or correct way to isolate and troubleshoot that component?

I pulled the housing for the relays, all looks good. One additional note... once I pull the negative battery cable (which resets the fans to OFF), they will not restart until I turn on the vehicle and the vehicle runs for a minute or two. I would assume (but may be incorrect) that if it was a short, the need to start the engine would not be the only way that the fans start up again. Even if I pull the negative battery cable and reconnect, the short would still exist and the fans would start back up immediately. Is that correct?

I can pull the relay housing back out (still attached to the wires) and reinspect, but nothing looked strange, burnt or atypical to my backyard mechanic eyes.

One additional observation, I have been getting knock sensor codes for about 3 weeks (on and off). I think they need to be replaced. I am going to do it asap (with a new wiring harness as well). Could that be related to the issue with the fans?

 

[Rivieraracing]

Never mind, I'm an idiot and was thinking about older vehicles!! Disregard what I said and listen to Jenna!!

 

[kses123]

I have had OEM e-fans for a while with a blackbear harness. Lately, they have been running on High a lot. Even when it is in the 30's. Definitely not normal. If I restart the vehicle, they usually will come back on low. But a minute of so later, they will cut on high until you shut the truck off. On a cold start, they won't kick on to low until the temp gets to 185 or something. Then they will run for on low for a bit, then switch to high and stay there. Wonder if the PCM is bad or the PCM is getting bad sensor readings?