2002 MCSS Cooling Fan Issue

[Stingroo]

Not sure if this is where this goes, but hi guys! Long time lurker, first time poster. I sold my Century awhile ago but my sister has an 02 MCSS. I love W-bodies for simple and reliable daily cars, but this one has me stumped.

She complained of it overheating, so AAA towed it to my house. No leaks found, no smoke from the tailpipe or anything like that, so I started to dig a little deeper. I noticed that when the AC was turned on, the fan didn't kick on. 

So I took the relays out and started to test them. Couldn't make them work. But when I put power directly to the terminals in the fuse box, both fans did work - so I could rule out the fans themselves and the fuses.

I replaced the relays, all three of them just for good measure, but no luck. The fans are still not coming on and the car got to 240 degrees before I shut it down. 

Where do I go from here? I'm not really that good at reading diagrams, but I do have an alldata subscription so if someone can point me in the right direction, that would be amazing.

Thanks! 

Edited March 6, 2021 by Stingroo

[Schurkey]

Relays should be controlled by one or more temperature switches and/or the control unit for the A/C.

ARE ALL THE FUSES GOOD?

Are the temp switches working?

Wire harness burnt/broken?

[Stingroo]

4 hours ago, Schurkey said:

Relays should be controlled by one or more temperature switches and/or the control unit for the A/C.

ARE ALL THE FUSES GOOD?

Are the temp switches working?

Wire harness burnt/broken?

Yes, all fuses good.

It seems to me the temp switch works, because the gauge is working. When you say "temp switches" plural, which other one should I be looking at? I see the one under the thermostat (awful spot for a lefty to reach...). What other switch is there?

No broken harness that I can tell. Haven't broken out the multimeter or anything, but it all looks good upon a visual. 

 

 

 

I pitted this question to a W-body facebook group as well and someone there said that the fan module could be the culprit. He suggested I unplug the coolant temp sensor under the thermostat, which should have triggered the fan to run as a default, but it didn't.

Thoughts on that? 

[55trucker]

17 hours ago, Stingroo said:

 

 But when I put power directly to the terminals in the fuse box, both fans did work - so I could rule out the fans themselves and the fuses.

I replaced the relays, all three of them just for good measure, but no luck. The fans are still not coming on and the car got to 240 degrees before I shut it down. 



 

So, if I read this correctly, you bypassed the relays & went directly to the battery to power the fans & with them running the engine overheated?

[Stingroo]

2 hours ago, 55trucker said:

So, if I read this correctly, you bypassed the relays & went directly to the battery to power the fans & with them running the engine overheated?

No.


I bypassed the relays to check operation of the fans, and they worked. So I replaced the relays. Started the car, but the fans were never commanded to come on by the PCM, so I turned it off before it overheated again. 

[55trucker]

I see, I misread your posting, I take it then if the fans are left running the engine doesn't overheat at all?

[Stingroo]

1 hour ago, 55trucker said:

I see, I misread your posting, I take it then if the fans are left running the engine doesn't overheat at all?

Correct. 

I spoke with my friend who is a used car tech at a dealership and has been doing it for 30 years. He thinks it could be the PCM itself. 

Bummer, but apparently you can buy them.

 

[55trucker]

Well, before you condemn the PCM do some simple tests for the cooling fan electrical circuit........

you've tested the electrical circuit from the relays (switch side) to the fans & they both? function properly?

 

now you need to test the *control* side of the relay circuits to ensure that

there is nothing upset in the circuit wiring from the PCM to the electrical centre that will NOT allow the PCM to engage the relays.

If after clearing the wiring for any faults then you can suspect the PCM itself.

You'll see that there are 3 relays, two control the on/off function to the primary & secondary fans & the third relay controls the variable spd function for the fans.

 

see the attached schematic..

*click on it to blow it up*

 

 

 

 

 

Edited March 7, 2021 by 55trucker

[Cutlass350]

2 hours ago, Stingroo said:

Correct. 

I spoke with my friend who is a used car tech at a dealership and has been doing it for 30 years. He thinks it could be the PCM itself. 

Bummer, but apparently you can buy them.

 

With all due respect, I know that being a car tech at a used car dealership must be very hard, because of the various types of cars that they get.
However, it's clear that your friend has very little, or minimal experience with older GM cars.

It's much more likely that a wire has broken.  Also, the wire loom has also likely "disintegrated".
Also, GM older PCMs kick the @ss out of just about every other older PCM that was every made!
Like all real complex products, there are great, good, okay, so-so, and cr*p parts in your car.
The wire looms are pure cr*p.  The wires are so-so.
Also, don't forget, we are talking about vehicle that is ~20 years old.  :-)

Turn on the AC.
Verify if the signal is at the relay.
If not, verify if the signal is at the PCM.
With a GM TECH-II scanner, you could easily do fan tests.  But, I doubt that you want to spend ~$500 and wait 1-2 months for a "China-clone" Tech-II scanner.  And, imho, there's no need for one is this case. 
 

Good Luck!
 

Edited March 8, 2021 by Cutlass350

[mfewtrail]

Since the PCM is located inside the airbox, I would suggest a good visual inspection of the wiring harness in that location(take the box apart). Rats love to nest in airboxes and a wiring harness nearby means they're likely to chomp on some wires in that location.

[Stingroo]

34 minutes ago, mfewtrail said:

Since the PCM is located inside the airbox, I would suggest a good visual inspection of the wiring harness in that location(take the box apart). Rats love to nest in airboxes and a wiring harness nearby means they're likely to chomp on some wires in that location.

Visual inspection here looks good. No corrosion on any of the pins or anything like that. 

[Stingroo]

2 hours ago, Cutlass350 said:

With all due respect, I know that being a car tech at a used car dealership must be very hard, because of the various types of cars that they get.
However, it's clear that your friend has very little, or minimal experience with older GM cars.

It's much more likely that a wire has broken.  Also, the wire loom has also likely "disintegrated".
Also, GM older PCMs kick the @ss out of just about every other older PCM that was every made!
Like all real complex products, there are great, good, okay, so-so, and cr*p parts in your car.
The wire looms are pure cr*p.  The wires are so-so.
Also, don't forget, we are talking about vehicle that is ~20 years old.  :-)

Turn on the AC.
Verify if the signal is at the relay.
If not, verify if the signal is at the PCM.
With a GM TECH-II scanner, you could easily do fan tests.  But, I doubt that you want to spend ~$500 and wait 1-2 months for a "China-clone" Tech-II scanner.  And, imho, there's no need for one is this case. 
 

Good Luck!
 

Oh I know. Everything in my house is a ~20 year old GM product. It's all I've ever known - lol

I have access to the real tech II at the shop. Will check it tomorrow to try and command the fans. 

[Wowitsfast]

I had this same problem with my 97 grand prix. The fans ran until I kicked on the AC then the fans would stop. I got passed off threw some crap around the garage. After calming down I noticed the harness that connects the 2 fans together was toasted from the exhaust manifold. Replaced that and it fixed my issue

I'm not saying that this is for sure your issue but it's worth a easy inspection.

I can't upload a photo of it but it's in the middle of the fans, connected to the shroud close to cylinder 3

[Stingroo]

2 minutes ago, Wowitsfast said:

I had this same problem with my 97 grand prix. The fans ran until I kicked on the AC then the fans would stop. I got passed off threw some crap around the garage. After calming down I noticed the harness that connects the 2 fans together was toasted from the exhaust manifold. Replaced that and it fixed my issue

I'm not saying that this is for sure your issue but it's worth a easy inspection.

I can't upload a photo of it but it's in the middle of the fans, connected to the shroud close to cylinder 3

That's a little different. AC on or off neither fan will work regardless of temp. Will take a closer look at the wiring, though. 

[Cutlass350]

2 hours ago, Stingroo said:

Visual inspection here looks good. No corrosion on any of the pins or anything like that. 

Fwiw, with the GM 2nd-rate wire/copper that was used, often the wire break is hidden inside the wiring jacket.
The ABS wires that go from the frame to front suspension are a great example.
Also, as I mentioned, the garbage wire looms often fall apart, leading to rubbing wires, leading to a broken wire.  That almost happened to the CPS sensor wires on my 2000 Old's LX5 engine.

In my 2000 Olds, I have a power feed that has a break in it.  It effects my HVAC electronic control and speed control (?and radio?).  I used a spare unused power feed in the fuse box, and jumpered it to the bad power feed line (via an inline fuse).  It's been fine for many years, and I didn't waste 4-10+ hours taking apart the dash/etc just to find exactly where the break is.

The mechanic that used to work at a nearby local garage was a GM dealer mechanic for many years.  It was great.  If I didn't have time, or feel like screwing with something, I'd just drop my car off there.   He is a great guy.  He got sick of being a dealer mechanic, and went the route of a being a local garage mechanic.  He was straight forward, treated every customer with respect, and is a nice person.  He was even knowledgeable about the Quad4 in my '92 Olds Achieva.  :)  I don't know where he went after that local garage changed ownership (former owner retired at ~70 years old).
The mechanic that is at now that local garage is a Honda and Toyota expert,  Which is good for the garage, since those are the most common vehicles they get.  But, as for my GM cars or Mustang, he knows very little about the common problems/issues with any of those cars.

Good Luck!

 

Edited March 8, 2021 by Cutlass350

[Stingroo]

Yeah I work at a Chevy store, so the guy who's going to look at it today is pretty good with that kind of stuff. He's helped me with some oddball issues on my C5 Corvette too. Hopefully he'll have time to get to it today and I can report back!

BTW - looked at your signature - I'd KILL for one of those DOHC 5-speed Achievas  

[Stingroo]

I just realized I forgot to mention that my little code reader is showing P0480 and P0481  - Fan 1 control circuit and Fan 2 control circuit 

[Schurkey]

Excellent.  That means you can follow a diagnostic procedure from the service manual.

[Stingroo]

Well.... it was indeed the PCM!

We went through the whole diagnostic for the codes and that's what it went to. Got a PCM from O'Reily's, cost $189, and we programmed it. The fans are working now!

Never in my life would I have guessed that. 

[Cutlass350]

I'm glad that you fixed it!
Yes, any part can fail.  That's why it's important to have the Dealer's Service Manual, and the proper diagnostic tools.

Imho, you should have done the more typical thing, replaced about $60,000++ of parts, including rims and tires (because, hey they are easy to replace), instead of doing things intelligently.

Congrats on saving another GM car from the soul-eating junk-yard! 

Btw, both of my Achieva's are not long for this world, because of rusting of the frames and unibody.  I replaced both back rear sub-frames a long time ago.  Also, it has been impossible to get the cats/pipe for the dual exhaust '94 for over 10 years.  I had to drive many hours go to an area in another State that didn't have emissions laws, just to have new cats and an exhaust put on.  No one would touch it, since they couldn't get order "replacement pipes and cats".

Here is the original ebay ad:
http://www.veryuseful.com/GM/94OldsAchieva/

Like many other W-bodies of the time, it had water leaks to the inside because poor body sheet-metal gluing.  Thankfully, it was only for the front passenger side.  I drilled holes in the floor, put a custom-made plastic riser piece over floor sheet metal to keep the carpet dry, and it's been fine since.  Yes, I cleared all of the water drain areas, and sealed the panels/areas with sealant.  But, that didn't fully stop water from getting in during heavy rain storms.  I also fixed the horn button.  It may have been a bad clock spring?
Otherwise, it was a loaded Achieva, power everything, and a 5-speed manual! 

Edited March 10, 2021 by Cutlass350

[Stingroo]

Relearn  complete. Car back to normal. The coolant elbow up top is leaking (probably because it got hot) so I have another project to do tomorrow.... but that's easy enough. I think every 3800 we've ever owned (about half a dozen or so) has needed those. lol