According to the wiring diagrams I have, it appears that the secondary fan is not intelligently controlled by the ECM; rather, it seems that the ground side of the coil is connected to the thermostatic fan switch and the A/C pressure switch. Is there some terminal on the ECM which can directly control this fan per the specified fan on/off values in the EPROM? I am not using the A/C right now, and I would prefer to be able to control the fans strictly according to temperature.

 

No the computer doesnt control the secondary fan. If you want the fan to come on sooner, either install a manual switch, or put in a lower temp switch for that fan.

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Not quite true Kevin. When the ecm detects a "high A/C pressure", the A/C is on, your vehicle speed is less than a specified speed AND your temperature is above a specified amount; the second fan will come on.

You need to alter the machine code to not test the "bit mask" for the high a/c pressure and then change the vehicle speed and fan#2 temperature, it will come on if you have have the A/C on.

 

I believe I have found the part of the machine code that involves the testing of the "High A/C Pressure" condition and I am hoping that I may have found a "bit twiddle" around it.

If my "test" works properly, I then will be able to tell people how you can control Fan#2 so that it only relies on having your A/C on, setting the maximum speed of the vehicle and temperature range.

 

This seems like an old topic, but still a good one. I am running my second fan off a Dodge 200 degree switch right now. I would rather have the ECM control it.

I saw a post by Grumpy recommending to run all fans of mechanical switches to reduce the internal ECM temperature. I really don't see much of a savings since the enable transistors only burn about 60 mWatts.

I am assuming that this topic was about the '730 code and that is what I am using. I looked through the hack file. I see what you are talking about by having the A/C on and changing the Fan 2 turn on/off temps and the modifying the A/C pressure switch.

One thing I noticed is that the A/C pressure switch signal acts as an input to sense the switch. It can also act as an output to turn the Fan 2 relay on.

Judging by the '730 ckt board schematic, this signal is input only. There doesn't appear to be a driver (transistor) for controlling this output.
One other thing. By turning the A/C on to enable the fan other code is executed due to the ECM thinking the fan 2 is on. IAC and stuff gets modified. I still have to dig deeper into the effects from this.

My main concern is that the ECM doesn't even turn on Fan 2 at all due to it looking only like an input. It seems like only the mechanical 238 degree switch or high pressure can force fan 2 on.

Just preliminay thoughts.......

J

 

60 here, 60 there, it does all start to add up.
Just this morning we were talking about ecm operating temps..
Don't forget heat is always an enemy of electronics. It seems most ecms run at 100dF, but some have been noted to run at more like 130dF. While no where near the breakdown temps, the thermal cycling itself has to be effecting the dompnents.

I see no need to run anything other then a GN rad fan switch, with an A/C bypass for turning it on with the A/C.
YMMV
FWIW

 

I agree with you that heat is not good for electronics. I still want to run a second fan via the ECM though. Heat is one reason I don't want to turn on two fan relays off one ECM fan control output.

I don't want to run a mechanical switch partly becuase I am using an LT1 intake and running out of places to drill and tap for the switch. And I would rather have the ECM control everything anyway.

I looked into the '730 schematics and code. It appears that the ECM only turns on fan 1 if the A/C is on and the A/C pressure is high.

If the A/C pressure gets high, the mechanical switch turns on fan 2 only. Also, another mechanical switch turns on fan 2 if the temp gets above 238 F.

So, as I see it now. The ECM pin D12 that attaches to the fan 2 coolant relay is there only to sense if the A/C pressure is high. It does not turn on fan 2 at all.

The code talks about fan 2 being turned on. I think that GM at one time had the fan 2 control connected to another pin for fan 2 control. So, it requires a code modification just like what is being talk about in the WBO2 thread. Where another pin is used for controlling or sensing stuff.

I need to figure out how the ECM pins are addressed in the code. I see that the are controlled with the SPI device. I just don't understand the addressing scheme completely yet.

Anyone know how it is done or where I could find some docs on it? I am still digging. I'll report what I find.

Thanks,
J

 

Junk, I've been very busy and quite ill, but I wanted to briefly respond since I had made a response over a year ago.

What you are finding is exactly what I ultimately found - the second fan is only an INPUT to the ECM. There is no direct output to the second fan from the 730 independent of the fan switch in the passenger head. There is code in the AUJP that suggest that if the fans switch is engaged that you then can have the 2nd fan controlled - but it looks like GM decided to have the fan switch just override the ECM regardless and the only that happens is the ECM is told when the 2nd fan is engaged. Who knows, maybe GM wanted to have the 2nd fan controlled by the ECM but "cheaped" out in the last moment.

So your alternatives are 1) manual fan switch, 2) install a lower temp fan switch, 3) wire the the 2nd fan in parallel off the 1st fan relay - but that may introduce it's own problems an prematurely burn out the fan relay.

Anyway, I need to rest, but I thought I should respond.

 

I appreciate the response Glenn. I hope you get well soon.

Well, I couldn't just give up on this one. I have been looking through the code to better understand what GM's intent was with FAN 2.

They definitely canned the idea after putting a reasonable amount of thought into it. If you want to have the second fan controlled by the ECM.......connect the negative side of the coil to pin F8 (an output). That is where they were connecting it.

All of your thoughts about the A/C stuff still applies. You can also leave all of the mechanical switches connected to it too.

I haven't tested it yet cause my '730 setup isn't running yet. Probably be a month or so. I'll post if it works or not.

J

 

I looked at the '165 ECM and how it would control a second fan. It would take a significant re-write and removing one of the present outputs.....like air sel, egr, etc. Also, GM really never intended that this ECM control 2 fans. Not much code for it.


J

 

My 165 ecm does'nt control my fan either.The diagram shows only a circut from the cooling fan switch to the fan relay which controls the fan.It seems like an input only,also.The only response from the fan is when I switch the fan constant.Then it will stay on or off.Why does tc have on/off temps for the fan for 165?

 

FWIW, I am running both of my fans off of one relay, which is controlled by the ECM.

I had to play with the ON & OFF temps a bit to get it to control where I wanted, but that only took about 20 minutes. I suppose the final test will be this summer in 100* trafic.

BW

 

The assembly code for GM ECMs contain A LOT of code and data for stuff that isn't used. It sounds like TC reports the information, but that doesn't mean the ECM uses it. In this case it does not.

As for running both fans off one ECM output driver......you increase the load by 2. I would recommend running one relay off that output and 2 fan relays off that one. That way you won't have to worry about both fans not coming on. I guess it all depends on how you wire it.

Anyway, I figured out how to have the ECM control the fans seperately.

Have fun,
J

 

I wonder why gm added code for the fans (aside from ac input)but did not have an ecm output for the fan(s).With no output there can be no fan control via ecm.Sinse there is no ecm fan control then tc should'nt have constants for it.So unless you add code for a fan control output the ecm is useless for fan control(aside ac input).

 

What ECM are you referring to? I don't use TC so I don't know what fan (1 or 2) you are talking about. The code in the '730 is there to control fan 1 but not fan 2. Just the '165 doesn't have much code for it.

The '730 has a lot of I/O that is unused. You can have it do whatever you want. The '165 uses all of the available outputs already. Maybe at one time (e.g before air divert or something) they were going to have the ECM control a second fan.

Mess with the source and you can make anything possible........variable rate (progressive) NOS, RPM deactivated line lock, wheel speed sensor (front tire) for traction control, and on and on.

J

 

Many of the constants and tables TunerCat has were from requests/feedback from users. I know because I have told TC about a number of constants and tables that I have found useful for tuning and they have happily added it.

I know I iniitally thought the Second Fan could be controlled by the ECM and before I started diving deeply into source code, it appears it would. Now that we know more, yes TunerCat could remove the enable temp for Fan2.

Also, as Junkcltr said, dive deep enough into the code, and you could make the second fan work as you prefer (with a freed up output - something guys who have ditched the EGR could consider), or just 're-wire it" so the second fan is enabled when the first kicks in.

 

I would hope that TC would leave things such as this in there stuff. That way if code enhancements are made avail, then TC can take advantage of them.

Glenn, if you have the '730 ECM I think all you need to do is hook the relay for fan2 to the F8 pin on the ECM.
The '165 is another story.

J

 

Ok,then why does tc even add cooling fan temp on/off ac on/off to the contants since the ecm does'nt control it.Dont they test what tables/constants the are adding to see if they work?That just seems iresponible to add tables that in no way can be used without adding code.What are they filler?What scares me is how many other tables/constants tc has that is non functioning?Am I missing something here .

 

Maybe the idea to control the secondary fan remotely was incase of an ECU fault/failure. In which case the manual switch would stop your engine from overheating.

Simon