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i had this same problem, but i cant think of how i fixed it...

Cliff8928 wrote:You can't read the temp with your OBDI scanner?

What do you mean exactly? Of course not. For OBDI Ford and GM , I use OBDI only scanners. I have an OBDII scanner, reader for OBDII. I'm missing what you may be getting at. I'm not having trouble seeing my engine temp. Coolant Temp Sender for the gauge is working fine. I'm having trouble getting the fan to come on when the engine REACHES a certain temp via my Coolant Temp SENSOR. Gotta be a connection problem somewhere I would think at this point.

Speedy, if you remember how you fixed it, I'm all ears buddy.

Then you just have one of those "code readers"? There are full-blown scanners that will read that data just like on an OBD-II car. I've done it on my '89. You can actually see if the temperature and if the ECM commands the fan on.

That's what I thought you might be getting at Cliff. I COULD go that route, but while I don't know the EXACT temp my car is hitting , I let it get about 3/4 on the temp gauge before taking off down the road on a cooling run since the fan never would kick on. That should be equivalent to about 250* plus , MORE than enough to kick the fan.

So, if I'm reading between the lines correctly here, are you hypothesizing that perhaps my ECM is not triggering the fan?

Also , the ECM kicks the fan on while in diagnostic mode, albeit not the same situation I know.

You think maybe I should test the ECM?

Not quite like that... The CTS reports the temp to the ECM, the ECM engages the cooling fan relay at the desired temerature..

If you can view what data the ECM is actually reading from the sensor, then maybe you can isolate the problem. Also you can do things like mess with the plug on the sensor to see if the readings change.

Also, if you completely unplug the CTS, you should end up throwing a code 15 which will cause the fan to come on.

It's only the old-school GM stuff that had a sensor that directly triggered the relay.

Also, the fan I believe should kick on at 210* F in the Quads. Now I'm sort of wondering about the ECM as it supplies a 5 volt charge to the CTS and when the coolant is low detects high resistance and when the coolant is hot SHOULD detect low resistance and trip the fan relay.

But then again, that could also be a poor connector causing the ECM to think the coolant is always cold. So I think I shall go ahead and try the pigtail first as it's the cheaper, simpler thing to try first.

Thanks for making me think that out Cliff. You make a good sounding board!

Yes,you're correct. I've been up since 5 am and thought about my post immediately after making it. That's why I corrected myself,lol. My bad.

I DID forget about unplugging the sensor and seeing if that trips the fan though. Quick and easy way to test the ECM I guess. Thanks again. Will try these things and report back.

The CTS is actually resistance to ground, not 5V like the MAP, EGR, TPS, etc...

Right. We're saying the same things in different ways.

Most engine functions are affected by the coolant temperature. Determining whether the engine is hot or cold is largely dependent on the temperature of the coolant. An accurate temperature signal to the PCM is supplied by the coolant temperature sensor or Engine Coolant Temperature (ECT) sensor. The coolant temperature sensor is a thermistor mounted in the engine coolant stream. A thermistor is an electrical device that varies its resistance in relation to changes in temperature. Low coolant temperature produces a high resistance and high coolant temperature produces low resistance. The PCM supplies a signal of 5 volts to the coolant temperature sensor through a resistor in the PCM and measures the voltage. The voltage will be high when the engine is cold and low when the engine is hot.

So, after chatting today on here, I went out, unhooked my CTS and wala, fan came right on with both new and old relays. So, I think we can assume the ECM is good and doing its job. I was already pretty sure of that. I think we can ALSO assume the pigtail , corroded though it is inside the one pin in the plug, is at LEAST making enough connection to let the ECM know it's THERE. And I could tell as soon as I unplugged and plugged it back in. Car ran like crap w/o it plugged in (of course) and great with it plugged back in. So, here's where we are at in my estimation:

Fan: Known good
Fan Relay: Known good
CTS: Known good
ECM: Seems to be known good. No other signs from ANY component pointing to ECM failure.
CTS Pigtail connector: SEEMS to be fair, but some corrosion in pins would warrant replacement.

If that doesn't do it, I'm at a loss except to start tracing wires to look for an open or break. Any other ideas Cliff or anyone?

Change the pigtail either way. If i saw there was corrosion on any of my pigtail pins, i would be changing it right away! Even the slightest bit of corrosion can cause serious problems. I should know, i spent over a year and a half working with car batteries. And a lil bit of corrosion there would cause a car to not start, so imagine what it could do with smaller pinouts Keep us posted on what happens Mike!

I think you should have a good way of scanning the ECM so you can read what data it is seeing.. You can get handheld units that do this, or PC based units which are actually cheaper!

I don't like the idea of replacing pigtails unless it's really necessary... But if you do just make sure it's a good weathertight connection. I would prefer just installing a new connector/terminals on the same wire if you have more room on it...

Connector

Terminals

well thats what i meant, its late and my brain doesnt work lol. I was refering to the pins and connector, for some reason i was thinkin that was the pigtail lol

90GTZHO wrote: i was thinkin that was the pigtail lol

That's because it is!

Don't even start talking about this wiring stuff, all you're doing is reminding me of when I had to build a new 88 Mitsubishi Starion ESIR engine wiring harness from scratch! Boo too tedious BS wiring work on cars, it's no fun!

Mike, if that doesn't fix the issue, I'd start looking at that ECM again...

Yes, I HAVE a scanner like the one you speak of Cliff. Unfortunately 95% of my business is OBDII so the scanner I purchased that does that is for OBDII only. I have two of the OBDI code readers that ONLY read codes too. One for Ford, one for GM.

My OBDII scan tool/reader is for all OBDII equipped vehicles.

And yes, the pigtail INCLUDES about 6 inches of new wire, the connector and new terminals. I kind of thought that was common knowledge. It's already put together too!



If the pigtail doesn't do the trick , I may have to go back to testing on the ECM.

So, the Quasar got the Claybar treatment today. MAJOR DIFFERENCE if I do say so myself. I think you may rather enjoy the following pictures! I do!