91 cadillac seville- service engine soon light

Last Edited By Krjb Donovan
Last Updated: Mar 11, 2014 07:59 PM GMT


Hi Rob,

I just purchased a 91 Cadillac Seville and I have to get an inspection sticker with in the next 4 days. To me, the car seems to be running fine however, on my way into work this morning my service engine soon light can on. Any ideas?

The codes are:


Thank you!



I don't have any service manuals dating back that far so I cannot assist you with the codes and if you are under that 4 day time line, you will need to take the vehicle into a service garage (not a dealer) that has diagnostic equipment for the old OBD (on board diagnostics) system. in 1994 GM went to the newer world wide standardized system OBD II. Most larger service centers have this equipment and can determine exactly what the problem(s) are. The codes are only a symptom. One problem can set off a number of codes in the history. When it says EO48 History, it means that what ever EO48 is, was set off as a soft code indicating there was a problem in that system, but the service engine light did not stay on permanently and was ignored. The service engine soon light not going out tells you there is a hard code and something that has to be serviced now. A loose gas cap can set off a variety of codes to give you an idea of the sensitivity. Let's say you have a code 13 and a code 34. The code 13 O2 sensor will cause a code 34 map sensor fault as well. So, you may have only one problem that cascades itself. Unfortunately, in it's current state, it will not pass an emissions test and without the proper diagnostic equipment and knowing what the codes mean, this is not something you can correct yourself. With the service engine soon light on, you will not get the optimum mileage and power out of the car either. There is no way to estimate a cost for repair without knowing what sensor or connection is bad, or if the ECM (computer) is bad and you will know all that when a proper diagnostic test is performed.



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