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Randall C
Randall C, ASE Master Tech
Category: Cadillac
Satisfied Customers: 12829
Experience:  ASE Master Tech, 32 years exp,Cadillac 6 yrs
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1995 DeVille: 4.9L..the service engine soon lite is..timing

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My 1995 DeVille 4.9L the service engine soon lite is on all the time , my mechanic tells me it has a 23 code with something to do with the electric spark timing but we have no idea how to fix it . Please help .
Hello, My name I Randall. I will do my best to assist you with your question.

With that code, the tech needs to follow the diagnostic flow chart. It could be one of a few things. Most commonly the igntion control module but.. if they did this and cleared codes and it returned? then they need to check the connections at the control module as well as connectors at the PCM ( computer) and if all checks out, it very well could be failed PCM but.. I do NOT want to say this is it till its confirmed they have followed the flow chart below. I can only say it is very possible you do in fact have a bad PCM. It is one of the possibles. Its a tough code to trace. It really does reuqire following the stpes shown to isolate the problem. At a quick galnce and by experience, yes.. the fist thing I would even go for is the control module. If in fact they did replace? it tends to rule this out

Customer: replied 6 years ago.
I only received page 2 of the 23 code diagram , I also need page 1, I will need to print both pages to give to my mechanic


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Customer: replied 6 years ago.
My mechanic did all the ground checks and followed the chart you sent me and put in another new control module also an ECM . The Caddy engine at idle revs up & down and the service engine soon lite is still on , it seems the engine idle is fine after driving several miles .