86VetteBill

I'll explain it as I experience it, but I can't figure out the next part....

Ok - I hop in and turn the key on. The car has been sitting or sometimes the temp gauge is up to ~180F. The radiator fan starts spinning as though I've hit 226F. I'm suspecting the temp sensor?

Here's the "next part": it seems (can't be sure) that when the radiator fan kicks on, the 4+3 won't go into overdrive?

Any thoughts?

TIA

93 ragtop

You dont have the AC or defrost turned on do you? Because they will both bring on the fan.

86VetteBill

I thought about that too when it happened. I switched from ECON to OFF and still happened no matter which mode I was in.

That would have been too easy! :crazy:

86PACER

From my 86 Shop Manual..

Coolant Fan runs continuously with the Ignition swith in RUN

1. Check for diagnostics codes 14 and 15. Use this site to check for those codes and to diagnose the problems of those codes. http://www.c4vettes.com/ecm.htm

2. If no codes are found, Check the Dark Green with White wire from the Cooling Fan Relay for short to ground. The Cooling Fan Relay is mounted on the inner fender behind the Front Driver's tire below the Brake Master Cylider. That wire runs straight to the ECM.

3. If the wire is shorted, repair the wire.

4. If the wire is good. Replace the Cooling Fan Relay. About $10 at a local parts store.

Hope this helps
:thumbs:


[Modified by 86PACER, 2:27 PM 4/5/2004]

86VetteBill

I'll check that tonight - I can't imagine the OD on the 4+3 is tied into this anywhere.

Bill

CFI-EFI

That is two problems, right off the bat. Check your owners and service manuals. Another poster said the fan was supposed to run with the ignition switch in the "run" position. I am assuming thats, "switch, on-engine, off". My '84 doesn't do that, but maybe that correct for your car.

Do you have an aux fan? Is it the main fan that comes on or the aux? The main fan is ECM controlled. Bad wiring or a bad relay is most likely the problem, if it's the main fan. The same is true of the aux fan, but it is activated by a switch in the left head, between the #1 and #3 spark plugs.

The gauge is a separate problem. The sender for the gauge is in the right head between the #6 and #8 spark plugs. Electrically, the gauge is independent from either of the fans and the ECM. Back to the owners/service manuals. It makes sense to me that the ECM may be programmed to not allow OD when running hot. The theory being, to keep the R's up when hot to run the water pump faster. Good luck, and...

RACE ON!!!

86VetteBill

Te electronic climate control doesn't have a NORM setting. As I mentioned, I pressed the different buttons: ECON, DEF, AUTO, and OFF, and it still ran when first started - but not every time I first start it. I'll have to dig into the book some more.

Tonight I checked out the 4+3 OD relay. What a mess form the bottom side. It's well known that these wires weren't long enough and can pull themselves out of the connector pack, but these wires look stretched. I can even see bare copper. I reconnected the relay and then pushed each pin on the bottom of the connector pack towards the relay for a better contact.

Has anyone re-connector packed these wires before?

When I mentioned the 226F temp earlier, which is when the fan is supposed to come on, that was just a reference. The temp hasn't reached that high yet.

FYI - there is only 1 radiator fan on my '86 L98, and the OD has always worked no matter how hot the motor has gotten (235 once! :nono: )

SO, the OD seems to be ok and the fan is imtermittent. I'll check that fan relay.

65Z01

Did you check for stored codes yet? Is the SES light On when you turn the key On and goes out when you start the engine?

Check the temp sensor below #6 & #8 plugs, that's the one that drives the coolant temp gauge.

86VetteBill

No codes - I just replaced the starter and had the battery disconnected for the weekend, so if there were any they're gone now and if there was an issue detected by the ECM, it'd have thrown a code again.

I'll see if it happens again this AM.

CFI-EFI

I was aware that you hadn't over heated, recently. I only mentioned the OD posibility, because of whatever is kicking that fan on, may also triggering other built in high temp "defenses". Obviously my speculation that OD defeat at higher temps, was one, was wrong.

If the fan were constant, I would suspect a stuck relay. Since you now say it is intermittent, I would go with the previously suggested, grounded wire, somewhere. More than likely, the wire leading back th the ECM. Also, possibly, the ECM? How does it run? The temp sensor in the front of the manifold, feeds the ECM. The gauge problem, should be unrelated.

RACE ON!!!

65Z01

Ah, sorry but I had read the fan symptom wrong; so lets see if I got it:
-fan sometimes comes on with key on
-temp gauge is ok
-car drives ok even when fan on
-currently no codes

There are several things that could cause the fan to come on with ignition on:
-the A/C pressure switch or wiring is open
-the ECM's coolant temp sensor or wiring is shorted
-there is a short in the coolant fan relay Grn/Wht wiring.

I believe the ECM would also bring on the fan in Limp Home mode but this should leave a stored code.

86VetteBill

I've got a little bit of an update. There's definitely a "connection" between the radiator fan running before the temp hits 226F and the OD unit on the 4+3 not working....(if the fan isn't on

As I drove the car over the past week, I listened and tried a few things (AC/Defrost OFF)(no aux fan on this car)....
1) If the fan turns on prematurely the OD unit turns off. This isn't fun when you're doing 70 mph down the highway.
2) I pulled the coolant level sensor wire (just in case) and the Low Coolant light came on, but the fan didn't.
3) I pulled the coolant sensor wore (between cyl 6&8) and the temp on the digi-dash went from a number (160F) to "Low". The fan did not turn on.
4) I pulled the cooling fan relay (on the left fender well) and shook it and heard rattling inside, so I replaced it. Didn't help.

I looked at the wiring diagram and from the cooling fan relay, there's 2 wires that go to the ECM and 1 to the fan. I need to look at the OD unit's wiring to see if they come close to each other and the OD might be feeding 12V to the relay causing the fan to come on, but not enough amps to also run the OD?

I know I'm really stretching here. Any input is appreciated. Thanks.

SunCr

Is overdrive disabled if the ECM believes the engine is overheating? Main fan is controlled by the ECM with a driver grounding the relay when the coolant temp sensor indicates 226 degrees or the fan switch on the a/c high pressure line indicates 230 psi (a/c on). The a/c fan switch is normally closed and 230 psi opens it - so if the wire was disconnected or open, the fan would run all the time. I don't think that's your problem. ECM won't turn on the fan above 40mph unless it senses that the engine is overheating. I'd check the coolant temp sensor signal below the throttle body with a scanneor if you don't have one, it should be about 3400 ohms across the terminals on a 70 degree day, engine having sat overnight. At 212 degrees, it should be about 185 ohms. If that's ok, disconnect the relay and see if the fan stops. Check the driver line for voltage (dk/green/wht) with a test light. Below 226, you shouldn't get one, but if you do, the wire is shorted to ground or the ECM is funky. No test light, then the relay is a good suspect.

86VetteBill

That sensor under the TB is such a pain to get to! But I like your ideas. I'll get the ohm meter out tomorrow. But, still, to affect the OD? I've driven the car after a coolant change. The temp went into the upper 230sF. And the OD was unaffected.

I suspect the test light will light at the relay. With the fan running (way below 226F) I pulled the (new) fan relay on the fender well and the fan stopped.

Thanks for the info!

SunCr

One of the great mysteries of the C4 ECM is the temp considered overheating at cruise - I've never been able to find it in any literature and all the manuals simply say, the ECM will turn off the fan at 40 mph unless the engine is overheating. My guess is that the ECM on your Vette is sensing an overheat condition because of a skewed Coolant Temp signal, turning on the fan and disabling overdrive.

86VetteBill

Well, preliminary test results are in... The shop manual walked me through "fan runs always". Even though that wasn't truely the case, it allowed me to test things that would cause the radiator fan to run when it wasn't supposed to.

The relay that I replaced didn't need to be replaced. The short story is that the "cooling fan switch" which is located in line on the high pressure side of the air conditioning line (located near cylinder 6 with a dark green wire and black wire). The dark green wire goes to D11 on the ECM causing a short to the radiator fan. The goofy switch is stuck "open"

But I couldn't find ANY procedures on how to remove the cooling fan switch! Anyone have any experience with this? Hopefully, it's just another $7 part.

Also, hopefully, this is somehow tied to the 4+3 OD issue too.


[Modified by 86VetteBill, 12:00 AM 4/18/2004]

SunCr

Someone else had a problem with this switch and had a difficult time finding a replacement - check http://www.acdelco.com for a part #. Hopefully, it's on a shrader so that it can be replaced without losing the charge. You might want to double check it by grounding the harness and seeing if the fan shuts off. Also, at least for GAGS, the shift relay shares a ground with the a/c control panel. If your schematic shows the same for 4+3, you might want to investigate that ground. Seems plausible that if that circuit opened, it might turn on the fan and shut off OD.

86VetteBill

Well, the fan control switch wasn't the problem. Glad I didn't have to replace that!! So, I'll get into the 4+3 OD wiring and switches to see, like you say, if they share a ground. Thanks for the interest!

86VetteBill

I'm approaching this problem from 2 fronts: Is the OD relay forcing the fan on or is the fan forcing the OD off.

I've cleaned up the wiring to the OD relay. Boy - those wires really get pulled out of the connector! I isolated the bare wires from each other with some electrical tape. The radiator fan is still coming on at, or soon after start up. The fan relay (on the left fenderwell) was replaced.

The shop manual says to ground the diagnostic terminal and does the OD light come on? Yep, then nope. Could be the OD relay. This morning, while driving in and the engine temp was 180F with the fan running and I pulled out the OD relay and the fan kept on running! :smash:

I'm still leaning toward the coolant sensor giving mixed signals? High for the fan to come on and low for the OD to stay off? Who knows. I'll have to see if I can capture some of the signals at the ECM.

Or should I just take this sucker in to be scanned?


[Modified by 86VetteBill, 10:03 AM 4/23/2004]

SunCr

Hate to see you give up, but my last guess, that a common ground between the a/c control panel and the OD relay may be wrong, though you might still want to review your Manual for common circuitry. Looking at the schematic I've got, the a/c fan switch is a 12 volt signal from the ECM only. When the fan switch opens, that signals the ECM to ground the fan relay. The test would be to ground the a/c fan switch (harness to ground) while the fan was running to see if the fan turned off. If so, the switch is bad; otherwise, troubleshoot the signal from the engine coolant temp sensor. Looking at the chart, the sensor should be 185 ohms at 210 degrees with more resistance the lower the temp. Check your schematic for the correct Pins but for '89, it's a 5 volt reference signal from Pin C10 back to Pin D2 for ground, so if resistance was low (high temp), you'd expect to see nearly 5 volts at the ECM. You could also check the driver circuit Pin C1 for voltage after you disconnect the relay. Shouldn't be any with the fan stopped, but if there is, the harness or dk/grn/white wire is touching ground somewhere or the ECM may have gone south.