donbrew

SnapOn should do it. Not an authority though. Could just need the SnapOn guy to show how, that's what they get paid for.

My understanding is: you only need a Tech2 to update firmware/software, other ScanTools can insert commands.

I have had Genuine GM Certified Technicians (plural) tell me they could not find my Airbag Controller, my RCDLR, my Rollover Sensor. The training sucks.

My vote is still with the ECM pin.

hhr11

Looks like you've tested mostly everything but I'm wondering how you know the ECT is good as you indicate in post 1. The ECM supplies a resistor pull up voltage and ground to the ECT. The change in the resistance of the ECT changes the supplied voltage from/to the ECM. The ECM then reacts to that voltage change to activate the fan relay. Did you check all the wiring and resistances of the ECT back to the ECM?

hpp700

hhr11 : is the resistor pull up voltage across the engine coolant temp sensor to the ECM ?
I see this as pins 61 ( low ref) and pin 50 (ect sig) on the cooling fan circuit diagram I have.
I believe the coolant temp sensor is good because the engine temp displays and goes to zero when the sensor is removed , but we'll check wiring.

donbrew :thanks for info on scan tool and I 'm following up with my tech

hhr11

HPP700. From my Alldata print out for 2011 (probably not the same as yours since you have a 2006 but function should be similar) The Pull up resistor/voltage side is pin 58 yellow wire ECM to ECT lead B. Ground is pin 4 ECM Tan wire to ECT lead A. Hope this is of help to you.

donbrew

The more I think about it; maybe GM did disable mode $08 so you can't turn things on & off without their Tech2. I am not sure about it. The Snap-On salesman would know.

Anyway the keyword is "mode $08", that's the mode that enable bi-directional control of the ECM.

hpp700

Ron7000 on Chevy Truck forum posted that you can "fool" the PCM by placing a 60 ohm resistor from +12V to the relay control lead on the PCM. It works. No code P0480. From this I believe the PCM is good and I have a wiring problem, but I get good continuity from all connections on the relay . I have to get this state inspected and get back on the road for work. Clearing the code will get it by inspection and it's averaging 20 degrees here so I won't need the fan till March.

donbrew

Have you looked into pin 47 on the ECM cable connector being bad?

hpp700

I get good connectivity ( zero ohms) from pin 47 on ECM connector to relay connector . But you're right that it probably is wiring. It's not that complex a circuit. Checking all wiring again. Thanks for your help.
I think I 'm close and will report the resolution.

donbrew

I have had an adult beverage or 2, but isn't good more than 0 ohms? When I touch the leads together on my dvom I get 1.6 - 2.0 Ohms, NO connection reads 0.L.