Cooling fan will not turn off

[livingez_123]

This makes not want to put electric fans on my Denali. Maybe some OEM fans and a aftermarket harness that doesnt connect to the PCM like maybe the painless system or the Flex a lite kit that has an adjustable controler.

 

[nlareau]

Blue PIN 42 is grounding someplace. If you disconnect the PCM do the fans turn off? If not, it is not the PCM. If it does shut off, definitely that PIN.

Sent from an ice cream sammich.

When my fans misbehaved, this is what "blue pin 42" looked like. Start looking here first.

 

[retiredsparky]

Sensor voltages are very low, usually 5 volts supply, less than that for the reference or analog return to the PCM.

This can easily be affected by any corrosion around electrical connectors. Vehicles that live in a winter snow or seaside area can have salt residue under the hood. That salt mixed with even small amounts of moisture can cause incorrect signals to the PCM or send voltages that are damaging into the PCM (12volt dc into a 5 volt or reference pin for instance).

Green or white powder or appearance is a sign of corrosion.

 

[tnoonan88]

Hi there, were you able to get a part number or identify the harness that you mentioned in this post? I'm having very similar issues (cooling fans staying on overnight, knock sensor codes coming up). I realize you posted this a couple years back but I haven't been able to find any other leads on the forums. Thanks in advance!

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

 

[Tahoe05chuck]

I am having same issue with my 2005 Tahoe. Replaced 5 pin fan relay (even though tested good), thought the issue was resolved but next morning same dead battery and fans running constantly. Pulled PCM, all appears good, no corrosion or signs of moisture infiltration. Once I connect charger, within minutes the fans come on an continue running until I pull the relay. Anybody have any luck in solving the issue?