Having issues with fan only coming on when the A/C is turned on. I performed a test of the #1 socket on the Fuse relay panel on the 3 fan relays as the Haynes manual says. I'm getting a reading on the #3 relay but nothing on the #1 or #2. It doesnt say anything about what to do after. I'm getting +5v to the new ECS. Is this telling me the wiring between the PCM and ECS are good?

I also jumped the pins under the dash and the fans came on. I'm stumped and man I hate electrical crap.

 

You should only get 5V to the harness connector for the coolant temp sensor, when the sensor is not plugged into it. Once the sensor is plugged in, the voltage will drop. The voltage will vary with the temperature.

You can test the sensor itself as shown on Shoebox's guide:

http://shbox.com/1/4th_gen_tech2.html#ect

Shoebox also has the complete 95 wiring diagram. Your car will be "late production".

http://shbox.com/1/fan_schematic_1995.jpg

 

Are you confirming that your PCM is commanding the cooling fans to come on? Keep in mind the OEM fans aren't programmed to come on until 227 degrees (235 for the high speed).

For diagnosing fan problems, take a look at Rob's guide on www.shbox.com

 

FYI, you would be better off starting one thread in this forum on the same subject rather than three... The moderators will be able to help you more efficently.

 

Cool, I got a new ECS in there guess it could still be bad. In that diagram do you know if the relay#1 and #2 control is in the PCM or is it a seperate piece?

I guess the only way to test that PCM is telling the fans to come is with a scan tool? Do the basic scanners do this.

Sorry didn't mean to offend, I am looking at this as a seperate problem. Fixing a head gasket will do me no good if the fans aren't working properly.

 

Man I hate reading diagrams. Let me see if I got this right:
The gauge has a wire that leads to the sensor on the head measuring temps.The ECS in the water pump sends a signal to PCM. Which sends a signal to the relays that tells the fans to come on? Does that sound right? Thinking I got a problem between the relays and PCM. I have done all the other test and they come out fine except there is no reading on the #1 socket of the #1 and #2 relay and I haven't tested the new ECS.

 

You have the system correct. The thing to do is use a scanner and see what the PCM thinks the water temp is. If it thinks the water temp is below 226F there isn't going to be a signal to the fan relays.

Check those pins again, this time looking for continuity to ground. It's been a while since I looked at the wiring diagrams but GM loves to switch the ground on and off instead of the power.

Che k the resistance across the two pins on the coolant temp sensor and compare it and the ambient temp to the table Rob has on his site shbox.com that should tell you if the temp sensor is even close. Do this on a cold or col engine so ambient temp is close to the water temp....

 

How about you let the moderators run things. This is a separate problem from his overheating and head gasket issues. There is nothing wrong with what you did. All you managed to do was embarass him into deleting the other thread.

 

Sorry for stupidity, When you say looking for continuity to ground do you mean one test lead to known ground and the other to the black wire on the plug and there should be NO continuity?

Thanks Inj. Didn't want to make anyone angry. Guess now I know when I get my fan straight I can start a Head gasket thread. This is a spare car so just trying to learn things on my own so I can use the extra money for go fast goodies. Hope to have it all lined out before Power Tour 2012.

 

Sorry guys, no offense intended. Just trying to be helpful. I've started a couple of threads before of similar cases and was told not to. Like I said just trying to be helpful.

 

I did the 5 and 6 jumper thing and the fans kicked on. From what I read it tells that the wiring and relays are good. Man I'm stumped. Seems like it would have to be the ECS. I'll test it today, its the only thing left.

 

Let's get a few things straight before we get too far off the beaten path.

Are you referring to the ECT as the ECS?

You said "Having issues with fan only coming on when the A/C is turned on. So you are saying the fans will never come on even if the engine is over heating by them selves (actually by PCM control)? Is this actually what you are saying?

If that is what you are saying, then did you confirm the actual temperature of the coolant reaches 227 degrees and the fan is still not on? or did you always shut it down before you MAY have actually reached that temperature? Keeping in mind the gauge is nearly always wrong or at the very least, it's hard to tell exactly what temp it is actually showing.

Have you ever tried swapping in a resistor in place of the ECT to see if that would make the fans come on? Let me clarify. As temperature rises, the resistanc of the ECT will go down. If you look at shoes' chart, you see at 77*F the resistance is 2796 ohms. At the top of his chart it shows at 212*F the resistance is 177 ohms. So at a lower resistance the fans will come on when the temperature it senses is at 227*F.

So rather than find the resitance and buy a resistor (you may need to later) you can simply unplug the sensor and put a jumper wire (paper clip) in the terminals. See if the fans then kick on. You should then see a CODE 14 for high temperature indicated.

Conversely if you simply unplug the ECT and run it, a CODE 15 should appear.

This will immediately answer if the PCM is connected properly through the entire length of wires to the ECT.

FWIW I believe a 147 ohm resistor (placed between the terminals with the ECT disconnected) from the shack should make your fans come on and not throw a code.

Incidentally, the only way to actually test the ECT is to check the resistance values at a given temperature as show in Shoes' table. In boiling water at sea level, the resistance should be 177 ohms +- 10%

 

I put the jumper on the OBDII plug (it's OBDI) and the fans kicked on. I put the jumper (paper clip) on the terminal of the ECT and nothing happened.

 

So ohm the wires from the ECT connector to the PCM connector.

 

Any idea which connector on the PCM controls the ECT. Cant find it on the diagram

EDIT>>>>>Scratch that.....Found it