Doing an engine swap, replacing a 1998 Buick 3800SC with a 1999 Pontiac 3800SC. One of the differences I have found is the Class 2 Serial Data wire that goes to the DCL. On the Buick it came from PCM connector C1-58 (green). On the Pontiac it comes from C1-59 (purple). I've looked at a lot of schematics for GM cars from this vintage, they all seem to use C1-58 or C1-59. Some might even use both.

For Class 2 Serial Data, I used wire C1-58 (Buick) on the Pontiac PCM (schematic shows C1-59). When I connect my Genisys tool. I get DTCs and data. However, Genisys offers two groups of Engine Data, Engine Data 1 and Engine Data 2. I only show data on Engine Data 2. The Engine Data 1 group is blank.

Is there a difference between C1-58 & C1-59? Are they redundant?

David Solakian
Manager/Technician
Yancey Bros. Co.
McDonough, Georgia, USA