1990 Cadillac Eldorado Biarritz reading shows the code e52. How do I fix?

Those are mem-cal codes, unless you changed the ECM the PROM (a separate part inside the ECM) has gone bad or the ECM itself went bad, if you just replaced your ECM with a used one you need to swap PROMS just remove the 2 screws and remove the plate then the PROMS. If this doesn't workYour best avenue is to remove the ECM then go to a parts store that sell Standard Motor Products they have an R+R program and will repair your ECM and PROM and send it back. I hope this helps. Take Care.

You will need it removed and sent out for repair.

check fuel pressure

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The Cadillac service manual says for the B terminal is a tan/black wire, for the E terminal is a white wire , for the R terminal is a purple/white colors may have faded! Any more trouble I got the book!

Hello: The ISC motor should be adjusted. The part that screws into the larger shaft coming out of the motor should be approximately 17 mm. The code does not have to be cleared for the light to go away. You should collapse the ISC motor and check the tps it shoud be -1 to +1 best at 0. Call me if you need further assistance. I have a 1984 Cadillac service manual. 662-449-7099.

Try this put key in switch leave on 15 min. switch off then crank this should reset the security code.

have you checked the fuses and test the voltage on the head light plug to see if you lost a ground or power