Code 26 is refering to the QDM that drives the TCC circuit. Check all fuses,
check all grounds. Check brake switch for proper operation. Any further
diagnosis would require a scan tool, basically to check the ECM for proper
Code 27 refers to a problem with the "mid gear switch" located inside the
transmission. Now I would start checking the connector going to the
transmission for good clean contacts. Quick check to see if it's the ECM or
the wires: disconnect connector at transmission. Using a test light, check
termial "C" and "B" for 12VDC, be sure ignition switch is "ON", engine
"OFF". If yes on both, look at tranny for problem. If no on both, check
wires at ECM and in between. If no on one and yes on the other, do the same.
If all wires, connectors and grounds check out, replace ECM.
I am also seeing that both these codes refer to circuit that get power
through the brake switch. I think I would start there, are your brake light
working? Are all your fuses okay?
No offence intended, but please check your info properly before suggesting
fixes or what to look for. This particular vehicle, 1989 Buick Century has a
3.3L V6, not the 3.8L found in the late 80s Park Avenue. Different engine
all together. I am looking at the DTCs for his particular car and my
previous post outlines what I think he should look for base on the info I
have in front of me. There is NO EGR run off the QDMs that are giving the
codes 26 and 27. In fact, from what I can tell, the '89 Centruy 3.3L doesn't
even have an EGR! (Looking at the vacuum diagram I can't see an EGR listed
and looking at the ECM pin outs I can't see an EGR terminal) So now you have
the poor guy looking for an EGR he doesn't even have. :(
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