[Aredecom]

I'm working on my son's Malibu. It's a 97, 3.1L, auto, 125,000 miles.

The thermostat is opening when it should, the water pump is pushing water, the coolant temp sensor was just replaced and has proper Ohm reading at cold and hot temps. All fuses are good and all relays test good too. The fans come on if I unplug the coolant temp sensor (although the car runs like crap with it unplugged) If I jump the Fan 1(location #12 on the fuse box) relay with a fused jumper wire from pin 30 to 87 both fans come on (seems like low speed). If I jump fan 2 (Location 14) from pin 30 to 87 passenger fan comes on (seems like high speed).

So the temp sensor works, all the fuses and all the relays are good, and the fans themselves work as well.

When I turn AC on and blower on high the fans do not come on. But that may be because previous owner removed compressor and put in an AC bypass pulley. Not sure about that...

Haynes says where the relays plug in the fuse box I should have constant power to pin 30. And I should have power to pin 85 w/key on. I do have power at both pin 30's, but don't get power to pin 85 with the key on, with engine running, or with engine running above normal op temp.

I do however have power to pin 86 for fan 1 with car on or off, and I do have power to pin 86 and 87 on fan 2 with car on or off. Which doesn't seem right.

Extra info, it has a new expansion tank cap, system is 50/50 coolant water, all air has been bleed out through the bleeder valve. Has good vacuum, good fuel pressure, full oil (not milky) do not suspect head gasket or lower intake manifold gasket. No coolant leaks either.

From the beginning of the overheating story: the car was overheating and overflowing from under the cap, my son kept adding water/coolant but never bled the air out. It kept getting hot, (never got to red because I told him these cars blow gaskets easy and to just pull over) The cap was bad so we bought a new one, refilled and bled the air out. Then the car held temp right at 1/2 line or just above at red lights. Indicating a fan issue. Since fans came on with sensor unplugged and relays and fuses tested good, we put in a new temp sensor. But still no fans. That's when I started rechecking relays and power at the pin locations in the fuse box and got some odd reading that didn't add up.

I'm really hoping there is something else that would cause this besides the PCM, is there anything else I can test, try, replace, etc besides the PCM? Is there another sensor besides the coolant temp, fuse, or relay besides what's in the under hood fuse box that might be keeping these fans from switching on?

Thanks in advance, I've already check everything the haynes manual says to check, but it doesn't say what to do if pin 85 doesn't have power with key on. I've read lots of overheating threads online and seems like most or from loosing coolant, not bleeding air out, bad relays or bad fans. I have none of that and am kinda stuck. Thanks in advance for any help/ideas!
Rob

 

[Starship]

Wow, that's a lot of info. You say you measured the resistance at the coolant temp. sensor but did you check the actual temp. reading with a scanner? When you unplug the sensor, BCM sets a code and PCM then turns on the fans to protect the motor. So, the control circuits from the PCM to the relays are probably okay. The A/C circuit won't do anything because it's also missing the refrigerant pressure or such. So, I'd guess it's the wiring between the sensor and the BCM or something internal to the BCM itself. It all depends on the actual temperature as read by the BCM.

 

[Aredecom]

I'm not real familiar with the BCM and all it controls. I know it is the source of some no start issues and anti theft or remote key issues. I'll have to do a little more research I guess.
Good point though, just because the coolant temp sensor is producing the right resistance for various temps, it doesn't mean the BCM is reading it right. I wish I had the sftw and ALDL-USB connector. It would have come it handy so many times. I guess I'll just have to take it to a shop with with the right equipment to get live feedback.
I know the OBDII scan doesn't tell much, but I did take it up to Autozone and get the engine codes read, and only got the one for the temp sensor, but that was because he was driving it for a day with the (new) sensor unplugged. He was trying to keep the fans on, but realized it ran bad like that. I left the battery unplugged overnight which erased the code and it has not come back, and the car runs really well, accelerates great, shifts smooth, again.
Anyway, good to know the PCM may be OK, looks like a BCM is a little cheaper. Can it be reprogrammed in order to fix it, or if it needs to be replaced does it need to be programed like a PCM? Sorry, just not sure on the function or process of fixing a BCM malfunction. I'll have to get it scanned and see what temp is actually being read and see if it's actually sending the signal to turn the fans on or not before I get ahead of myself here.
Thanks for the reply, let me know if there is anything I forgot too.

 

[Starship]

A decent scanner is a must for DIY nowdays. My first one was from AutoTap. Then, I got an AutoXray unit for my Saturn ION. I haven't had an occasion to hook it up to my Malibu, though.

You'll need to take it in for the BCM replacement, if it turns out that. It's still entirely possible that you've some sensor wiring issues. Or, you just haven't got it hot enough for the fan to kick in.

 

[DrivenDaily]

You mention that there's never any power on 85 but there is on 86. 85 and 86 are the two ends of the coil so there will be power on one side and ground on the other to complete the circuit. I'd say that 85 never having power is good, but you need to unplug each relay and ensure that 85 actually has a good ground path. It likely does, but it's such a simple test that it will only cost you time.

You have a '97 and I don't have the schematic for that, but I do have the schematic for our '08-'10 vehicles. On ours there is a third relay that switches between serial/parallel for the two fans, effectively switching them from low to high speeds. Instead of the 4-pin relays the ser/par relay has 5 pins with the extra one being a NC terminal. Here's a link to DropBox where I have the schematics. I paid $20 for them shortly after I got my car, then about a year later discovered this forum and have shared them with others.

http://dl.dropbox.com/u/4191695/08_chevy_malibu_complete.pdf

Look on figure 18 at the top.

Temporarily, just as a stop-gap measure, can you use either a wire or resistor to jump the sensor terminals? This would serve to trick the coolant circuit into thinking that there's a constant HOT signal, forcing it to turn on the fans and maybe still drive well.

Remember, the schematics above are not for your vehicle but might help you, since they are still GM. Companies tend to keep a wiring protocol for consistency. Ford does things a little differently but they're fairly consistent year to year on how they design them. GM is the same way.

 

[Selsdaddy]

I have a 99 3.1l and i have the same problem. my fans wont kick on by them self and itd causing my motor to overheat. iv changed the cap, thermostat, water pump and all fan relays. they still wont kick on?

 

[Starship]

Since Aredecom is MIA, I don't know what his outcome was. In his case, he also replaced the coolant temperature sensor (not to be confused with the one for the temperature display on the instrument cluster). The thing is that the troubleshooting should really start with a scan tool that can read the BCM parameters.

 

[Selsdaddy]

Im going to replace the coolant temperature sensor an see if that does any good. I dont know much about the scan tools?

 

[Starship]

You can try that, or, you can take it to a reputable dealer or independant shop and have it diagnosed for a fee. I like to get my hands dirty but not when I don't have the proper tools.

 

[Aredecom]

Well my sons car has continued to overheat. The fans do come on sometimes, sometimes they don't. He's still adding water and bleeding air out daily. He also got to check engine code pop up, P0300 random cylinder misfire, and P1651 PCM fault (quad driver 2) or Cooling fan relay 1. So we took it up to a shop and put it on a diagnostic computer. Results were PCM was reading the right temp, fans came on when they were supposed to when in the shop( but don't always), and tech said, it's probably the intake gasket and/or the head gasket. He suspected problems with the heads or head gaskets because of the random cylinder misfire.
So I put a radiator pressure tester on it. He had a good steady drip coming off the transmission pan from underneath. All related hoses and coolant connections above that area were not leaking. I finally found the leak coming from the side of the block between the throttle body and EGR area. It's kind of dirty and hard to see, it could be just the intake on the side there where they just used silicone (most likely) or could be the head gasket too. He's ran it hot several times and could be either or both really. At this point the repairs are more extensive than the value of the car, and he's looking for something else, and probably just sell this one for parts. Which is sad, because he's put 8-900 in new parts in it over the past year. It's got dents and faded paint, a rough interior and no AC. So he doesn't want to waste any more money or time into it.
Not the greatest news, but figured I'd do a follow up for anyone else having the same type of problems. Thanks everyone.

 

[Starship]

So sorry to hear that it didn't work out. Thanks for the update.

 

[thecody301]

New to the forum and I am having the EXACT same problem with my 99 Malibu. It sucks that this thread didn't come to a better resolution than to sell the car! I have no power to pin 85 on my relay and the only diagram I've seen anywhere on here that says where pin 85 gets its power from says it comes from "Power Distribution Cell 10". Which I have no idea where that would be. I'm going to pull the thermo switch connector, since it makes the fans come on, and check pin 85 again. This will tell me if its the PCM kicking the fans on or some redundant failsafe from elsewhere. Will post back on this thread tomorrow with results. If anyone out there has the fix for this I would love to know before I break down and get an aftermarket fan controller.

 

[Starship]

Aredecom mentioned DTC "P1651 PCM fault (quad driver 2) or Cooling fan relay 1," which sounds to me like a short on one of the four circuits controlled by the quad driver module, not necessarily the cooling fan relay itself.

I'm having a hard time understanding the nomenclature like "pin 85" and "Power Distribution Cell 10." See the following wiring diagrams:

Cooling Fans
Power Distribution, 1 of 2
Power Distribution, 2 of 2

These are for a 3.1L Malibu. If yours has 2.4L, let me know. Also, if you let us know what troubleshooting you've done so far, we collectively may be able to give you more relevant suggestions.

 

[Starship]

Sorry, I actually meant to say something about there being multiple relays but had to interrupt my lunch. So, I didn't quite understand which "pin 85" you've measured and why you expected a voltage to be present.

I'm not sure how the relays are labeled in the engine compartment fuse block but they should be:

12 - FAN CONTROL RELAY 1
14 - FAN CONTROL RELAY 2
15 - MODE CONTROL RELAY

Looking at the the control coils, pin 86 is the top, hot side and pin 85 is the gound side that the PCM toggles. As the engine coolant temperature rises (based on the ECT sensor input), the PCM will first command (via a quad driver module) the fans in the serial, low-speed mode and then eventually switch them over to the parallel, high-speed mode. The fans may run in the low-speed mode with the vehicle off, again based on the ECT sensor input.

If you'd like to delve into the ECT sensor circuit, just do a search on this forum and elsewhere. If that circuit is shot, an "aftermarket fan controller" isn't gonig to address the underlying problem. It's probably best to take it to a shop and get it properly diagnosed. Good luck.

 

[thecody301]

Thanks for the diagrams. Sorry about the confusing dialogue. I was referring to the different pins on the actual relay. What you're saying is correct in that the powered side of the relay is pin 86 and the grounded side (controlled by the PCM) is 85. The Haynes manual has this information wrong. So that having been figured out the hardest of ways, I have no fault codes and I have power to all the correct pins. The fan was jammed due to a collision at the bottom of the car and the fuse was blown. I've jumperwired the relays and have gotten the fans to work. I've also gotten them to turn on by pulling the wires to the coolant temp sensor (which I have replaced). So I am convinced its either a software problem, or this quad driver module you speak of. Can you tell me what a quad driver module is and if i can replace it?

Thanks

 

[Starship]

A "quad driver module" (QDM) is part of the BCM (not individually replaceable). I believe the BCM on your Malibu has two of them and thus it can control upto 8 circuits (by grounding them). These circuits cannot handle high current flow and thus they are connected to relays and solenoids. If, say, a control coil or solenoid has a short between adjacent wires causing the current flow to go up, a QDM fault occurs with a DTC like P1651. If you suspect this is happening, I suggest taking it in to get it scanned/diagnosed.

P.S. That should read PCM. I don't know why I said BCM. I must've been marveling at the BCM circuits too much lately.

 

[thecody301]

I see. Well from all the information I've been able to collect and with the troubleshooting I've done, combined with what your telling me about how sensitive these QDM's are to current overflow, I am almost positive that I have a PCM problem. I will get the car scanned for any codes it may have stored, but since I've worked on it alot recently there may not be any due to removing the battery cables. Here is the thing. It cost $99 to get it looked at at chevy. The PCM is only $120 flashed and ready to install. If I get the fault code when I scan, I will forgo the diagnostic and just replace the PCM. I would hate to give them $99 just to have them tell me to replace it anyway. When I called them they told me that it could very well be the PCM so I'd rather gamble on the chance to save money. My goal is to end this post with a solution to this problem so others can save money and all the hassle I've been through trying to get this fixed.

 

[DrivenDaily]

I'm really interested in the outcome. I expect to keep my '09 till the wheels fall off (well, maybe) and it's likely that a lot of how yours is designed is still present in ours.

 

[Starship]

If I get the fault code when I scan, I will forgo the diagnostic and just replace the PCM. I would hate to give them $99 just to have them tell me to replace it anyway. When I called them they told me that it could very well be the PCM so I'd rather gamble on the chance to save money. My goal is to end this post with a solution to this problem so others can save money and all the hassle I've been through trying to get this fixed.

It's your call but I'd get it diagnosed properly. I lack the resource to tell which relays and solenoids are hooked up to each QDM but they do. A new PCM needs to be programmed or the vehicle wouldn't even start. Plus, there's a chance that the existing problems will damage the new PCM.

 

[ryan22soy]

well i dont know if you got your problem fixed or not but i have the same thing as for the leaking on the side i had that as well and just replaced the water outlet. people kept telling me it was the head gasket but i just fixed that and it wasnt so i finally found the leak. when i would squeeze the upper radiator hose coolant would squirt out when i removed the old water outlet it was smaller and didnt have an "O" ring/gasket i replaced it no leak any more. but my fans only turn on when the car gets to hot i dont know about if the A/C kicks the fan on i thought my main leaking problem was from the A/C but nope it was just the water outlet.