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Well Done Kevin..Thanks (nt) (archive)
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Posted by George Mann on March 31, 2002 at 07:12:00:

In Reply to: Check Control Module - advanced course posted by Kevin on March 30, 2002 at 20:43:14:


Some may have seen a message posted earlier this week on "ESD Regelt" and my response about that message possibly indicating a fault in the check control module... well, as fate would have it, less than 24 hours after I posted that message, I got the same dreaded message! OK, time to take some of my own medicine. I pulled the check control module today and began to do some serious triage. For those who have cracked the cases on the CCM, you'll no doubt recognize a highly symetrical design. This is for a reason... there are about 30 separate, but identical test circuits in the CCM that check everything from your brake lights to the key in the ignition. Every single one of these test circuits is set up as what is known in the business as a "current loop". That means that the system sends a current through the closed loop of the and measures the voltage drop across a precision resistor. If the drop is out of range, you get an error. Not to difficult. Anyway, to debug my CCM, I took the cases off and put it back in the car and started the engine. Immediately I got the ESD Regelt error. Using my multi-meter, I started testing the voltage at the precision resistors. All were the same... accept for 1. Hmm. I pulled the CCM and put it on the bench. Again using the multi-meter, this time in ohms mode, I measured the precision resistors. Each bank of precision resistors has 4 2K ohm resistors and 1 1K ohm resistor... again, nice symmetry. Problem was, one of my 2K ohm resistors was 2.7K ohms... since I did not have any spare precision resistor networks laying around, I instead calculated that an 8.2K ohm resistor in parallel with the suspicious 2.7K ohm resistor would bring the value back down to the required 2.0K ohms. 30 seconds of soldering and the new resistor was in place. I left the case off the CCM and plugged it back into the car. Hey, no more ESD-Regelt! I checked the voltages and all were exactly the same - as they should be.

Anyway, thought I would post this since this is one of those gremlins that could be hard to track and cure... it's sort of the analog to the capacitor fix for the cluster. Of course, this problem could have been solved by purchasing a new or refurbished CCM... but then again, we're all trying to keep that cost of ownership down!

Kevin




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