Code 56
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Junior Member
Joined: Feb 2023
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Code 56
Hi hammerpete here . I'm working on a 1990 buick reatta 3.8l auto with a check engine lite on for a code 56 quad driver b . I can not find any info on this , some say a bad ecm , but from what i've found out so far is the these 4 drivers check the statis of 4 differant circuits be it milli amps or ohms for stuff like delay head lites, radio when the key is turned off.. I don't want to replace the ecm and not fix the problem, thats a waste of the customers money. He wants to sell this car but it will not pass smog in california because of this stupid code which has nothing to do with smog.any help would be much appeciated
Senior Member
Joined: Sep 2010
Posts: 1,230
Hi Pete,
Trying to find relevant info for Reatta was a challenge, to say the least. Having been in your position many times, can appreciate any help, so here goes.
I believe that is a body code "E".
You might check GRN/BLK wire coming from the ECM to the fan hi speed relay in underhood panel.
You might check the other , DKGRN/YEL to the AC relay also from the ECM. We are looking for opens or shorts.Also the white wire from the AC low press sw.
You might check the EGR solenoid for short or open
The can purge sol for same
And the Divert valve sol
The checks suggested are all controlled by the #2 Driver in the ECM.
Hopefully this will provide some guidance , and last but not least, look very carefully for possible pins backed out at ECM connector.
This does go back a while when a tech didn't have the assistance of OBDll and these things needed to be done to avoid destroying a replacement ECM.
Trying to find relevant info for Reatta was a challenge, to say the least. Having been in your position many times, can appreciate any help, so here goes.
I believe that is a body code "E".
You might check GRN/BLK wire coming from the ECM to the fan hi speed relay in underhood panel.
You might check the other , DKGRN/YEL to the AC relay also from the ECM. We are looking for opens or shorts.Also the white wire from the AC low press sw.
You might check the EGR solenoid for short or open
The can purge sol for same
And the Divert valve sol
The checks suggested are all controlled by the #2 Driver in the ECM.
Hopefully this will provide some guidance , and last but not least, look very carefully for possible pins backed out at ECM connector.
This does go back a while when a tech didn't have the assistance of OBDll and these things needed to be done to avoid destroying a replacement ECM.
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Junior Member
Joined: Feb 2023
Posts: 8
It took me some time to trace out some if the wires, then I found the someone had taken the rt hi speed fan relay an put in a dead hole.
When i installed it in the right place as soon as you turn the key on the fans start up on hi speed. Now looking back the climate control
center wasn't working right , sometimes the correct display an other not,.now things work but the air only comes out the mid vents
no floor or defrost . A/c and heat work. So I guess the problem lies in eihter that climate head or the cllmate modual. Any ideas and
avaibility of parts? Thanks hammerpete
When i installed it in the right place as soon as you turn the key on the fans start up on hi speed. Now looking back the climate control
center wasn't working right , sometimes the correct display an other not,.now things work but the air only comes out the mid vents
no floor or defrost . A/c and heat work. So I guess the problem lies in eihter that climate head or the cllmate modual. Any ideas and
avaibility of parts? Thanks hammerpete
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