The primary cooling fan on my 89 will only come on these days when I select AC, or when the Diagnostic Terminal is grounded (Both fans then come on). The displayed coolant temperature seems to track and lead the oil temp indication so I believe the Coolant Temp Sensor is working and delivering a reasonably accurate input to the ECM. The auxillary fan comes on when the temp gets above 235F. The Aux Fan is controlled by a Temp Switch on the LHS of the block just to the rear of #1 spark plug. None of the wiring diagrams I have show a Cooling Fan Temp Switch in the Primary Fan cct but there is a similar looking sensor on the RHS of the block just to the rear of the Oil Dipstick. It has one green wire coming from it that I can't trace. When I ground this wire with the engine running, nothing happens. Can anyone tell me (1) what this device is and (2) what I might try next to get the primary fan to work? (I have already replaced the Primary fan control relay).

 

Is this the wire you are talking about?



I have a thread titled, "Where does this wire go?" for which I received replies which indicate this wire runs to the EGR switch (highlighted by the small box in the picture).

 

The primary fan is controlled by the ECM. It reads the CTS, and in 1989 once it sees 108 C, (226.4) it send a signal thru pin C1 dark green with white stripe to the primary fan relay. Check the green wire for 12+ volts once the vehicle hits 108 C. A scanner could also tell you if the ECM is calling for the fan. Could be a faulty CTS, circuit wiring, ecm malfunction, or any number of things associated with this circuit. Get a scanner and start observing.

 

Unless the a/c is on at which point the fan switch on the high line will open at around 220 psi or about 145 degrees (with subcooling it's actually 10 degrees less) at the Condenser and that will signal the ECM to turn on the Main Fan. It will keep running until the Pressure drops to 190 psi or 134 degrees (more like 124 - if you want to see what it is, put a digital thermometer on the high line). Both numbers are well below the thermostat which is needed to reach an optimum coolant temp. That's why the Condenser is in front and the 1 inch gap between the Condenser and Radiator is all that's needed to maintain sufficient coolant temperatures. If you keep the a/c on, your idle and low speed coolant temps will be 8 to 12 degrees less than if it were off. If they're not, something is broken.

Aux fan isn't controlled by the ECM and can easily overburden the low speed alternator output if run with the a/c on. In addition, cooling the a/c charge too much won't squeeze enough gas through the orifice or metering device to keep the Low Pressure Switch contacts closed so the compressor will cycle and your vent temps will be higher. Leaving it as designed works best; assuming you want a functioning a/c system.

Scanning will show you the Coolant Temp Sensor input which is different from the Display. Display signal is from a Thermistor in the Right Head. A 5 degree difference isn't unusual. The accuracy of the Coolant Temp Sensor begins by seeing what it is after it's sat overnight. It should be at ambient as should the Air Temp Sensor. Start it up and it should rise until the Thermostat opens (195 is stock); fall back a few degrees once it does; and then rise to the Main Fan threshold or 226 degrees. Once the Fan comes on, the temperature should drop. If not, something is broken - it wasn't designed to heat up with the Fan running.

If you want to see what the Aux Fan does, block air flow with a piece of cardboard or something similar and that should trigger it. '89 Spec is 228 degrees.

 

The sensor in the head is for the dash display.

The ECM uses a sensor in the front of the intake manifold under the throttle body. It has two wires vs. the single wires for the other coolant temperature sensors.

 

Has it got hot enough to trigger aux fan ?

Your info says the main cooling fan circuit is intact and working as it should, but you are either getting incorrect gauge info from sender in passenger head or incorrect info coming from the ECM's coolant sensor at front of intake.

 

No, not that one. It is a single green wire coming from a sensor threaded into the block just tothe rear of the oil dipstick. From a couple of the other responses, it appears to be the temp sensor used to feed the instrument display.

Thanks anyway.

 

Thanks. Any recommendations on a source for a scanner?

 

Buy this cable:
http://www.reddevilriver.com/aldl.html

Download this software:
http://www.ttspowersystems.com/DataM...ownloads2.html

Best scanner ever, and software can be used for 20 logs for free.

 

How did you insert the picture? I would like to do this for another problem I have.

 

Are you asking me? I just copy and pasted links from another website.

 

Yes, I understand that. The reason that I ask about the aux fan is because it comes on 10* hotter the main fan.
As I said, your main fan circuit is good, so either the gauge info is off, or the ECM's sensor is not reading correctly.

 

I have a free account with Photobucket to store pictures which I may want to post in a forum.

The picture is edited with Irfanview (free) picture editing software on my computer and then uploaded to Photobucket.

When I want to post a picture in a forum, I go to Photobucket and obtain the picture link for forum posting. It will look something like this: [XXX=http://s256.photobucket.com/user/Clark_Savage_Jr/media/Automotive/Bustedwire_zpsb761f69b.jpg.html][/XXX]

Note: The XXX is really the letters URL. If I had typed in URL, it would have displayed the picture instead of the text.

It's really quite simple once you've done it a couple of times. You upload your picture to Photobucket, the select your picture from those in your library, click on the link (it will automatically remember the link on your clipboard, then paste the link into your posting).

If you have any problems, let me know and I'll try to walk you through it. BTW, Irfanview is a great picture editing software program and it is free on the web. I use it a lot. http://download.cnet.com/IrfanView/

Regards,
Rich
Gig Harbor, WA

 

Thanks Rich. This is very helpful.

Gord

Ottawa, Canada

 

Rich:
Can you walk me through it. I created a Photobucket account, uploaded a picture, copied the URL, but when I went to paste it into a newe thread, it just pasted the text.
Thanks
gord.leona@rogers.com

 

The sender you are talking about only feeds the temp gauge. The ECM grounds the fan relay when it reaches temp. You can check the circuit by grounding that wire. If that check out the ECM is not providing a ground.

 

The 1988 version must be a little different, on my application the Fan Switch is located on the drivers side head between the #1 and #3. That green/white wire travels to the Fan Relay that powers the fan facing the nose of the car.

 

Yes it differs by year, 90 IRC up have two relays both controlled by the ECM.
Here is what my 91 looks like..My 86 was set up like yours.

http://forums.corvetteforum.com/c4-g...s-working.html

 

This should be require reading. I cant imagine diagnosing a C4 without a proper scan tool. Ive had Datamaster for 10 years. Still use it. A lot. When my old AKM cable stopped working a couple months ago, I got the one from red devil. Very nice.