rcssr

93 Convertable Cooling fan will not come on and lets car overheat. I am able to cool it down by turning on the AC or Def to engage the second (primary?) fan. I have replaced both fan relays, the temp sending unit it the front of the engine and all fuses relative (two 30 amp under the hood, 15 amp on pass side of the dash). I thought the fan motor was toast but if you run direct power, it runs fine. Can it be the engine ECM and if not what else could possiby be the cause. I am at my witts end with this, you can't let it idle (even in traffic) without overheating. Radiator is full and water pump is new last year. HELP
Bob Smith

THE 383 admiral

Are the fan grounds ok.. what about the fan switch sensor and lead to the fan switch sensor..

65Z01

On the main fan relay ground the input from the ECM, with key on.

If that brings the fan on check wiring between that relay point and the ECM.

C4orce2

After I had the LS3 hot cam crate engine installed in my '92, I had some issues with the new fans not always coming on when the AC turned on. Instead of trying to figure out what the problem was between the fans, my two computers and the computer interface, we simply decided to hot wire the fans. Now I control when the fans are on exactly the way I want to. You might find this solution to be the easiest and you may love it like I do if you try it. Good luck!

Cliff Harris

The ECM uses the coolant temperature sensor to determine when to turn on the fans. Check the sensor and wiring.

Both fans should turn on if you ground the diagnostic pin on the ALDL connector.

You can check if the ECM is turning on the fans by looking at the control voltage on the fan relays.

Cruisinfanatic

how high does the temp get?

79C3tnd

I have the same issue with mine. I haven't had a chance to test the coolant temp sensor yet, but I am pretty sure that is my issue. But regardless, as mentioned above, I simply put a toggle switch under my dash that can easily and comfortably be reached when driving. I never liked that the fans kicked on at such a high temp, so when driving in traffic i just switch the fan on, well before the "factory" setting of 228. Just makes me feel better to have it running cooler, regardless of the high temp setting the factory built in. No cooling issues at all now

RollaMo-LT4

Until an actual temp is posted, nobody knows for sure you even have a problem.
99.9% of the time if the fans works when you turn on the A/C, then they will probably work when the car gets to the factory set temp to command the fans to come on.

It might make you feel better, and that is all that matters.
But you didn't have a cooling issue before either if every thing worked as expected and the temp never got over 230°F - 235°F

They will work at the factory settings for over 100k miles without any issues or damage.
The coolant doesn't reach the boiling point until 260°F.

Paul Workman

I just recently went through that problem myself. Turned out to be the fusible link (behind the battery on mine). Consult your FSM and get out your digital multimeter.

There is a fan relay/relays with a connector on it that you can pull off and do some preliminary testing. The power for the fans comes from the battery via a fusible link (see your manual).

Check for battery voltage at the appropriate power pin (usually the heavier gauge wire, if you have to guess). If you have battery voltage there at the relay connector, then the fusible link is good.

Then the question is does the relay work? If you have two fans, swap relays and see if the fan comes on when the engine is up to temp. If it does, then you have a bad relay.

If you have but one fan, you'll only have the one relay, so swapping can't be done, unless you have a spare handy (which you probably don't, I'd guess). So, you'll have to ground the black lead of your digital volt meter and pierce the insulation with the sharp point of the red lead probe and see if the ECM is sending batter voltage to the relay. If it is, and the relay is not working, then you know it is the relay.

Now, if you don't have battery voltage from the ECM to the fan relay, then the ECM is either not providing any, or there is a connection between the relay connector and the ECM that is faulty.

As mentioned, the ECM depends on temp sensor current to determine when to activate the fan(s). So, you could probe the sensor and see what if any signal voltage is being sent to the ECM. If it is ZERO, then the sensor is probably kaput, or the wiring or connectors between the sensor and the ECM is open somewhere.

If the ECM has what it needs, but fails to provide a relay signal, then there might be a bent pin or other connector problem at the ECM, or even the ECM could be fault (but I doubt it at this stage of the game)
See what ya find and get back to us.

P.

Cliff Harris

This is backwards. The ECM applies GROUND to the relay to turn it on. You can force the relay to turn on by applying a ground to the relay pin connected to the ECM. This will not damage the ECM (it's an open collector output, for the technical types...). As I said earlier, it's easiest to ground the ALDL diagnostic pin, which will tell the ECM to turn on the fan.

You can fool the ECM into thinking the coolant is hot by disconnecting the CTS connector and shorting the two pins of the wiring harness side together. If that causes the fan to come on (as it should), then the CTS may be bad.

Cruisinfanatic

of course the op isn't responding now

rcssr

OK it stopped raining so I can get back to the problem. Did I mention that what I know about relays and ECM's would fit in a thimble? Thanks for all the replies trying to help me. Here are the updates as the problem is not solved and now maybe worse.
I replaced the sending unit in the front of the motor with no change, I jumped across the two wires with no affect as well. I switched the connectors on the two identical fan relay's as suggested and the AC fan still came on so I know both relays are good ( I had previously replaced them anyway). I ran power directly to the positive wire for the coolant fan at the relay connector as suggested (called the secondary fan by the GM schematic) and the fan came on and ran fine, so I know the fan motor is OK. The blue wire comes from the ECM and as suggested I grounded it with no effect (did the same with the green wire that comes from the ECM to the AC fan relay (GM calls it the primary fan). Since it read zero voltage I fail to see what grounding it would have done. FYI: all of this was done with the key in the on position. Are we thinking ECM yet?

Now the bad news: Out of stupidity I jumped the pink (hot) wire to the green (no voltage indicated) wire at the fan relay connector. There was a very tiny connection spark (not a short spark) and something went 'click' in the vacinity of the front of the motor. Now the AC fan does not come on at all. The relay was NOT connected when I performed this stunt so I did not fry that. What could I have done now? My 71 never had these issues...UGH

rcssr

False alarm, I just blew the 5 amp fuse located on the passengers side of the dash. The AC fan comes on again when you run the AC or defroster. I have 4.9 volts at the hot lead of the temperature sending unit, which I think is OK. If I jump power at the relay connectors from the main red power lead to the power lead of each fan they run fine. Of note is that when I try to jump power from the smaller red wire (which gets power from that 5 amp fuse) to the fan power lead it blows that fuse (either connector). I am guessing that it only uses less than 5 amps to trigger the relay but when I try to run the fan off it the fuse blow as the fan motors use more than 5 amps. Just a guess but makes sense to me. What now?
By the way I did check the 20 and 30 amp fuses in both fuse boxes located near the batter. All good

rcssr

Where is the ALDL diagnostic pin??

65Z01

ALDL is located under driver's dash on the right side. Remove the cover and jumper (paper clip) pins A&B (upper right).

Wow, it's tough shooting this type of problem w/o a FSM which calls out function of the various wires.
What are the wire colors into the main fan relay? And what is the wire color into the main fan?

rcssr

It is not under the dash unless I have to remove the lower dash pane to access it?? Would it be in a different location on a 93?
The wire colors are as follows:Red/Blk power to the primary fan & Pink/Blk power to the secondary fan (this is the one that won't come on). Primary power to both relays is Red. 5 amp fused link to the relay's are both Pink/Blk (smaller gauge wire than the primary red wire. Primary relay wire to the ECM is green & secondary relay wire to the ECM is Dk Blue/Wht. The coolant sensor wire to the ECM is yellow (must be working as the dash guages work fine showing temp).
I am reluctant to blame the ECM but I am running out of culprits. Maybe I should hit it with a hammer and see what happens!!**

Paul Workman

Sheeeiiittt!!! And, I knew that too!! You are correct! A ground is provided to activate the relay. (Memory is a terrible thing to depend on. My bad.)

rcssr

I have voltage at the temp sending unit and jumping them does nothing. I can not find the ALDL unless it is inside the lower dash trim that is material covered. I grounded the blue wire from the ECM to the secondary fan relay (that is the one that does not come on) and the fan came on and ran fine. Does this mean the ECM is bad?

rcssr

On a lark I jammed a paper clip into the two connections of the temp sensor and both fans came on (only with the engine running, not with just the key on). I had a feeling that I may not have done a good job of jumping it out previously and I was right. Since it is new I discounted it but it appears to be a partial culprit at least. I am going to put another sensor in and see what happens. I hope this ends this nightmare.

Old Ben

Have you checked the wiring at connector C138? The inner parts of the connector may need to be cleaned or the blue/white wire may have seperated.