markfothebeast

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?

markfothebeast

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

markfothebeast

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.

markfothebeast

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.

markfothebeast

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.

markfothebeast

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.

markfothebeast

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.

Allaboutelectric

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