I've been reading about the cooling fans on certain late 90s/early 2000's GM 3.4L vehicles not turning on. I have this problem on my 2004 Chevrolet Venture. It does not need the intake gasket or headgaskets replaced. The radiator fans simply do not turn on when the engine begins to slip past the operating temps near the center of the temp gauge (when stationary). I've been reading about it for the past couple years and the only logical explanation I found was in relation to a resistor in the PCM that fails causing the fans to not function when the PCM sends out the "on" command. However, I have no information to determine if that's a true statement. The other possibility is that the engine only requires use of the fans at a ridiculously high temperature. Just like a Cadilliac V8 I had worked on - a dealer I talked with mentioned that the fans only operate at 230f. However, this was on an all aluminum engine. Some engines stay cool enough just with the radiator coolant flow unless it is hot outside. But my 3.4L does not quite operate that way. The use of the fans would keep the temps within a safer operating range when at idle (I tested this theory with a jumper wire at the relay). The temp sender could also be at fault but I have no CEL.

Has anyone found a fix for this common problem that haunts many GM mini vans?

 

I've noticed that the 4 prongs relays could be unintentionally installed backward.

 

On low speed I believe fan 1 relay powers out through the main fan relay which powers fan 2 on the same circuit. If one of the relays is faulty it appears that neither fan will have a completed circuit on low speed. The relays for fan 1 and 2 can be reversed accidently. Pin 85 and 86 can be reversed but 87 and 30 can only be powered directionly from what I have read. I do not know if that is true although. I typically wire up relays on 87 as the power input.

Both the pos and neg battery cables that connect to the starter and block were badly corroded. I cleaned these connections where multiple wires merge but have not determined the outcome. I'm going to check the continuity between the PCM wiring and relay wiring that controls the fan relay operation if nothing has changed.

 

Still no luck. The fans are supposed to turn on when the A/C is on. I tested the relays with a 9v. The continuity between each relay is there when plugged in. My only other option is to test the wire running to the PCM.

 

No responses for the fan issue??

Here's my latest deal. For anyone that is looking to fix the fans, the BEST method to ensure that the relays/wiring/fans are all operational and the PCM is triggering fan operation, simply unplug the engine coolant temp sensor and turn the engine on. This will turn the fans on. The A/C won't even turn on my fans. This would have saved me a lot of electrical testing.

My next test is changing out the ECT to see if that solves my issue. I am having random resistance readings from it. This also controls many engine functions including the reading on the temp gauge. Symptoms of a failing ECT are hard cold start, rich running conditions, and false temperature readings, similar to a carburetor choke in some ways.

 

As for the relays being installed in reverse, I don't think that would cause any harm since the pins are in a diagonal position. 12v to either corner would still trigger the electromagnetic terminal to close.

 

I solved the issue. I purchased a new engine coolant temp sensor. Behold! About 2 - 2.5 lines from the center of the temp gauge to the right is where the fan starts in low and soon after kick in to high and the engine temp works its way back to one dash before the center line on the temp gauge.

 

I have the same issue with my gm 3.4
I already replace the coolant temp sensor
B

Here on the bottom is the new coolant temp sensor and on the outlet is a temp switch witch I adapt to make the fan work by temp it is ground to the LOW speed fan relay . any comment ?
oth fan work ( HIGH AND LOW ) with the scanner command . It doesn't have any leak or bad head gasket. Just it not kick on at right temp Im mean gauge needle stay on only with AC on but by engine temp it turn on when the needle is 3 mark over the half . it scare me
the only logic reason to me is something inside the pcm is not working right. I was thinking to buy another pcm and send it to someone who can change the fan temp parameters
on alldata I found the temp for the fan kick on is 235F but it doesn't make sense to me when the engine have a 195F thermostat . thermostat star open to 193 and full open to 200 but 35 degree difference is a lot
I test my car and take the risk only to see how it is working and fan turn on in low mode by temp at 245F . how gm make this terrible bad design
IM STILL LOOKING FOR INFORMATION ABOUT
Im running low in options
I love my car but running it daily with the AC. low my MPG ridiculously from 22 to 16
any idea ?
Thank you in advance

 

This is what i found on mine, the engine will start to overheat when not moving fast or ac not running. I monitored fan speed only see high speed with ac on. After that i chose to change the relatively cheap temp sensor located near the thermostat. no help still over heating. Then installed parallel resistor pot to artificial tell ecm the car is overheating to my supprise no low speed fan ever came on but at 222 deg !! high speed fan finally came on. This is beyond my comfort level as192 is desirable area as thermostat tried to do. Conclusion low speed fan output from pcm is no longer functioning, this line is still used in high speed fan operation as well as all 3 relays and both fans must be working to get high speed full 12volt per fan. The ecm is self is expensive and risky to put in another ecm, so for now i have decided to switch out my modification because ecm will see the funny reading from the temp sensor and tho code po116 if you fiddle with the input , so i can switch it in once the car is warm or simple turn on the ac and high speed fan runs. By the way the gauge will read zero if po116 gets triggered and run the fan on high speed, simple clear the code with code reader and will return to normal. it is a rare case that you are going slower than 20mph sitting still and not running the ac. Might replace ecm someday but with over 200k miles i will do the work around for now. I have had other work arounds with this 3.4 as the drivers side door wont lock from remote wire shared from the passenger door restored that function. Also ac will not get cold unless i run back ac on at least position 1. AC will go into overpressure and blow at the popoff. Probably orfice screen thing. Still have high speed at 222 degrees in case i forget. By the way high speed fan is triggered by high freon pressure not ac so ac must be charged in order for it to turn on the fans , will be about 25 seconds after ac is turned on before fans turn on then there will be a delay and fans stay on for a bit after ac turns off. Other option is to thro in an arduino to control low and high speed fans as i wish. Leaveing temp sensor as is to keep ecm happy but simitanously feeding arduino input, However keeping the ecm also connected to fans via diodes so that if other conditions such as ac operation or temp sensor malfuction will trigger fans as well. arduino 7 dollars Ecm hundreds still will need to program it to bring down temp setting, they have always been to high in my opinion. But without low speed it will shorten the life of these engines. so be aware of whats goin on, need at least a warning light.

 

Yes, the ecm has firm ware the low speed and high speed are too high to begin with , Secondly low speed output only engages with high speed on mine due to faulty ecm. Solution, simply add your own relay to directly engage the fans on high speed all the time the key is on. I know this is extra ware on the fans but you will see a nice 192 being regulated by the thermostat as it should be. New ecm and firmware adjustment will cost me over 500. I'm over 210k I don't care if my fans have to work full time they do anyhow when you run the ac.