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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / August 2005PING::Ian
Ian, Can you give us some clues as to exactly how the TDM (theft deterrent module) works on GM cars? Several of us want to remove these rather troublesome devices on our project cars. In particular: (1) is the passkey recognition system the only input which trips the TDM, or are there others? (The function of the door lock circuitry is a little vague) (2) We can bypass the resistor sensor with a precison resistor. That will solve some of the problems, but are there other steps that should be taken? (3) At some future moment, the TDM may fail, and a functioning one may not be available...Is it possible to get rid of this altogether? (4) Is the cranking fuel signal to the ECM from the TDM really a square wave, or does this terminal on the TDM just go to ground? Can one force the ECM to give fuel during cranking without having to use the TDM signal? We all would appreciate any help you might be able to give us in getting rid of this quirky piece of electronic overkill.. Thanks > Ian, > Can you give us some clues as to exactly how the TDM (theft deterrent > module) works on GM cars? > Several of us want to remove these rather troublesome devices on our > project cars. This is not my area of expertise, but if you give me the year and model of cars, I'll pose your questions to the guys in our shop that have experience with these systems. Ian Thanks, Ian... These may bridge a few years. Mine is a 1990 Reatta. Riviera had similar electronics. Other models may be involved as well. Most of us hate this system and want to totally disable it. Next in line is the Teves brake system which is a wonderful exercise in overengineering. > (1) is the passkey recognition system the only input which trips the > TDM, or are there others? (The function of the door lock circuitry is > a little vague) The Passkey recognition system "is" the only input. The door lock circuitry is part of "the other" form of security on the cars which ends up blowing the horn, flashing the lights, etc. > (2) We can bypass the resistor sensor with a precison resistor. That > will solve some of the problems, but are there other steps that > should be taken? I talked to the "guru's" at work, and their response was that this will take care of the passkey problem. They have used this method many times. You may already have this info, but in case you don't, here are the 15 key pellet resistances. 1: 402 2: CN....523 3: FW....681 4: GP.....887 5: KA.....1130 6: N5......1470 7: UN.....1870 8: XB.....2370 9: GA.....3010 10: NP....3740 11: FY....4750 12: C5.....6040 13: XY....7500 14: KB....9530 15: UW...11800 > (3) At some future moment, the TDM may fail, and a functioning one > may not be > available...Is it possible to get rid of this altogether? The response I got was that they could not remember ever replacing a TDM....nor had they ever completely bypassed the system. > (4) Is the cranking fuel signal to the ECM from the TDM really a > square wave, or > does this terminal on the TDM just go to ground? Can one force the > ECM to give fuel during cranking without having to use the TDM signal? There are two signals from the TDM. The one to the starter relay just grounds the relay, that would be easy to bypass. The other is a fuel signal, but the manual is not specific as to what sort of signal it is. It definitely does not appear to be on the "data bus line". The service manual is extremely vague. My only suggestion would be to probe that line with something like an oscilloscope and see what you get out of it. Sorry that I can't be very helpful in this area. Ian > We all would appreciate any help you might be able to give us in > getting rid of > this quirky piece of electronic overkill.. > > Thanks > > (1) is the passkey recognition system the only input which trips the > > TDM, or are there others? (The function of the door lock circuitry is [quoted text clipped - 51 lines] > > Ian Thanks millions...This is very helpful. |
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