The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Anyone know how to test a 7747 ECM? 5v or 12v for CES light?

*GOY* · 12-12-2004, 10:56 PM

Here's what I have:

No CES light when the ignition is on the on position.
Can't run codes. The light just plain never lights.

I've replaced the bulb with a working bulb. I've resodered the joints on the board for the light, and tested it on the board - it works when 12v is applied to it. (Didn't burn out bulb)

Here's the question - how should I go about testing the wiring/ecm for failure? My first thought was to pull the ECM, then apply the required voltage to the 5th pin (I think it's A5)... but I'm not sure if...

A) I should apply 5 or 12 volts
B) If I do that, will it work even then, or does that light share a common ground that requires the ECM to be plugged in too illuminate.

Any help on diagnosing a fried ECM or bad wiring?

12-12-2004, 10:56 PM	#1
GOY Banned Join Date: Nov 2004 Posts: 37	Anyone know how to test a 7747 ECM? 5v or 12v for CES light? Here's what I have: No CES light when the ignition is on the on position. Can't run codes. The light just plain never lights. I've replaced the bulb with a working bulb. I've resodered the joints on the board for the light, and tested it on the board - it works when 12v is applied to it. (Didn't burn out bulb) Here's the question - how should I go about testing the wiring/ecm for failure? My first thought was to pull the ECM, then apply the required voltage to the 5th pin (I think it's A5)... but I'm not sure if... A) I should apply 5 or 12 volts B) If I do that, will it work even then, or does that light share a common ground that requires the ECM to be plugged in too illuminate. Any help on diagnosing a fried ECM or bad wiring?