I have a Cadillac CTS (2003) that would not turn on and the key was stuck in the ignition. The dealer states that it has a bad ECU as a result of the battery cables being replaced incorrectly after a purchase of a new battery. The dealer claims that the cables caused arcing which ruined the ECU. The battery was replaced months prior, however, due to a constant battery drain (uncorrected by the dealer).

The arcing problem was not discussed until after I informed the dealer that the ECU was covered under the Federal Emissions Warranty.

Is there any way to disprove the dealer's claims regarding the battery cables?

I have a Cadillac CTS (2003) that would not turn on and the key was stuck in the ignition. The dealer states that it has a bad ECU as a result of the battery cables being replaced incorrectly after a purchase of a new battery. The dealer claims that the cables caused arcing which ruined the ECU. The battery was replaced months prior, however, due to a constant battery drain (uncorrected by the dealer).

The arcing problem was not discussed until after I informed the dealer that the ECU was covered under the Federal Emissions Warranty.

Is there any way to disprove the dealer's claims regarding the battery cables?

No, probably not.
Do you have proof the cables weren't replaced incorrectly?
If the ECU was damaged by a voltage spike, that is easily detected upon visual inspection of that module.

The proof we have is that the car never evidenced a problem with the battery after replacement. Further, we took it to another dealer yesterday and they reported no evidence of arcing. So, they are going to replace the part under the warranty. Thanks for your help!