Ok, well maybe not the fix OF the century but a fix for a Buick Century. Follow this Real Fix to see how a code 26 for the Quad Driver Circuit was diagnosed and repaired on this 1990 Century.
Vehicle
1990 Buick Century Custom 3.3L
Title
Code 26, Replaced Powertrain Control Module
Complaint
The customer states the check engine light is on.
Cause
Connected a scan tool and found code 26 – Quad Driver Circuit. With the key on, engine off, connected a fused jumper between the diagnostic link connector terminals A and B, observed the evaporative emission (EVAP) purge solenoid, the low speed engine cooling fan relay and the torque converter clutch solenoid, and found there was no audible click heard from the EVAP purge solenoid. Connected a test light across the EVAP purge solenoid connector terminals and found the test light illuminated. Disconnected the fused jumper from the diagnostic link connector and found the test light was still illuminated. The test light should have been off. Disconnected the powertrain control module and found the test light was no longer illuminated. These test results verified the powertrain control module was faulty.
Correction
Replaced the powertrain control module, cleared codes, performed a road test and verified the vehicle operated properly.