Subject: Re: 160 stat by BillH on 2011/9/4 15:41:41
Quote:
Strick wrote: One more tidbit of info, there is a VSS that tells the ECM to turn off the fans at about 35 mph. How do I know this? I put a manual set of switches in my cockpit that bypasses the ECM and grounds the signal to the relay that turns on the fans. If I forget to turn the fans off (back to normal) and I go above 35 mph the check engine light comes on which tells me the ecm senses a problem with the VSS.
That's strange,Tom. The fans are controled by the Quad Driver Module #4. The VSS is not in that circuit. QD4 gets commands from the ECM on the temp sensors and fan clutch relay. Then the QD grounds the relay(s). The QD also looks for voltage faults but will not throw the check engine light. It will however throw code 28 when you use the manual switch because energizing the relays puts voltage into the QD without a command from the ECM (and that throws the 28 but no SES light).
I've had the manual switch on my 92 for 4 years, never get the light or fan on as you describe.
Assuming that you have the switch wired into the green/white, blue/white (or both) wires at the relays, the fans should come on with the manual switch closed just by turning the key to "on".
I have seen the fan and light come on like that with a bad EGR valve (intermittent).
