Radiator Fans only working with A/C on

[MrsMcNastys]

OK so we have done the ECM coolant sensor swap with no change in problem.

Went back and verified fans, relays wiring again everything as it should be.

Fans only activate with A/C operating or pressure switch connector unplugged.

Was able to figure out engine data from A/C system control screen to verify ECM knows engine temp to activate and it does know correct engine temps.

Soooo ... we are back to square 1. Having a second ZR-1 available is a great resource as we will be swapping chips and ECU to determine if that is the problem.

Special thanks to Marc Haibeck who took the time to help on the phone, this one is a head scratcher for him also.

Ed

[c4koh]

Interesting to read. Since my analog gauge and my digital gauge do seem to both be working, and my fans weren't turning on, I also suspect that even if I did swap the Coolant Temp Sensor, then I'd still have had the issue.

If the digital guage reads 235, then I'd like to presume that the ECM thinks it's 235 too... and if so, if it's not switching on the fan, then there must be some other reason...

Of the replies so far, my hunch would be with a loss of grounding. In other words, assuming that the 235 reads true, the ECM flags 'ON', perhaps something between there and the fans isn't tripping... whereas the AC switch does trip to switch it on...

I wonder if it's feasible to test the ECM 'ON' (without a Tech 1, isn't there a way to ask it to test it too??) to see if that's the issue? (lack of good ground)???

Steve

[Franke]

The grounds are important for the ECM to command the cooling fan relays. I would also verify the wiring from the CTS back to the ecm just to make sure its not bad. You should also be able to read the CTS resistance at the ecm plug looking back to the CTS to help verify continuity.

[MrsMcNastys]

Thanks guys,

Haibeck confirmed what we already figured - that the relays, wiring, fans etc all work off the same circuit from the ECM from E6 and D11 wether they are activated by the engine temp or the A/C request.

Seems like all that can be eliminated as the problem. The fans ground fine and work great under A/C request, the computer "grounds" E6 and D11 to activate the relays under A/C request. Disconnecting the A/C request switch immediately activated the fans.

ECM knows coolant tempurature as demonstrated on the A/C parameters check so CTS (new from Jerry's) has not "shifted out of calibration" as stated in FSM.

We might have a bad cooling chip or the ECM may also be going - but that is really down to less than 1% probability.

Ed

[XfireZ51]

'How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?'

Sherlock Holmes Quote

I'll look at the chip if you want.

[LGAFF]

Gordon Kilibrew?

[c4koh]

Originally Posted by MrsMcNastys

Thanks guys,

Haibeck confirmed what we already figured - that the relays, wiring, fans etc all work off the same circuit from the ECM from E6 and D11 wether they are activated by the engine temp or the A/C request.

Seems like all that can be eliminated as the problem. The fans ground fine and work great under A/C request, the computer "grounds" E6 and D11 to activate the relays under A/C request. Disconnecting the A/C request switch immediately activated the fans.

ECM knows coolant tempurature as demonstrated on the A/C parameters check so CTS (new from Jerry's) has not "shifted out of calibration" as stated in FSM.

We might have a bad cooling chip or the ECM may also be going - but that is really down to less than 1% probability.

Ed

I'm not so sure this reasoning is 100%. As the diagram shown in the FSM (and posted by LGAFF), the ECM controls the fans to be on with the AC request from the pin C8, and in this case everything appears to be working. C8 does make ground according to that diagram.

The ECM would seem to therefore be working: its programming logic working in so far as switching AC on triggers the pin C8. I would doubt that the logic is only working in some places... and the ECM surely needs to be working for the other two fan relay pins (C6 and D11), otherwise likely it wouldn't work at all. So my opinion would not be a bad ECM, though of course it's not impossible.

My hunch does remain that of grounds: perhaps there is a good ground created when the AC is switched on [being the ground from the AC switch on circuit 450 Black]... and this works, clearly. This being said, I can't see (though will look more later) how that circuit affects the fan relays... but still.

But perhaps when the control to the cooling fans is only via the ECM (i.e. absent the control of the AC] then here there are insufficient grounds, and therefore lack of power to the fans.

The ground to check would seem to be the circuit 151 Black in any case...

Does that sound plausible??

Steve

[WVZR-1]

I would think you could maybe pin down the problem by just grounding the primary fan relay. If the fan runs then it would indicate there's a problem internally either to the PROM or the ECM. It's nice to have the luxury of the second ECM/PROM but how similar are the PROMS? Same source? Who knows. I think the grounding of the primary relay to start the fan would be certainly the easiest diagnostics to start with. Just thinkin'

I don't see anywhere it's mentioned that it's been confirmed. I only see the operation confirmed by the AC. Maybe I've overlooked something here.

[XfireZ51]

After re-reading this,by any chance did you ground the A/B terminals(as for reading codes) of the ALDL port and then turn ignition "ON"? Fans will come on then and that would be going thru the ECM and grounds.

[Franke]

Originally Posted by MrsMcNastys

OK so we have done the ECM coolant sensor swap with no change in problem.

Went back and verified fans, relays wiring again everything as it should be.

Fans only activate with A/C operating or pressure switch connector unplugged.

Was able to figure out engine data from A/C system control screen to verify ECM knows engine temp to activate and it does know correct engine temps.

Soooo ... we are back to square 1. Having a second ZR-1 available is a great resource as we will be swapping chips and ECU to determine if that is the problem.

Special thanks to Marc Haibeck who took the time to help on the phone, this one is a head scratcher for him also.

Ed

Is there really a problem here? Based on what I read in the FSM, it looks like the primary fan should come on at 234 degrees F + if AC is off. Engine oil temp also factors into the fan request as well so if the temps are not as high as the FSM indicates there would be no fans request from ECM.
You indicate the you were able to figure out engine data from A/C system control screen to verify ECM knows engine temp to activate and it does know correct engine temps. Just curious if it met these FSM parameters?