Code 26 is for the knock sensor. I had to replace my ECM on my 03. Gerlone said that the error code comes and goes. Before spending the big bucks on a new ECM, do the exchange of the left to right and right to left with the knock sensors. If the error code comes back but it is for the other side sensor it is the sensor that is bad not the ECM.
Unfortunately it is most likely the ECM but I would do the swap to make sure.