The ECM threw code 21 for ignition system malfunction. There are no
drivability problems except that fuel mileage may be lower. I haven't
calculation it yet, I am just going by the mileage and previous gauge
position. The power transistor fails the continuity test. Power and
ground look ok to the ignition module. The manual calls for a logic
tester to test the ignition signal to the ECM Is this possible to
have a bad ignition power transistor without any drivability problems
or can there be another cause for the code 21?