Cadillac Repair: 1990 Cad. Seville, digital volt meter, caddy shack

Question
Good morning once again Bill. Iwent to the independent who had worked on the car. he checked the connects says they are aok. He did give me the codes that were showing up and had a question. trouble codes were B120 and B334. He also wanted to know about the CPS (control power supply) He said it was supposed to be in the dash but he could not find it. He got his info from schematics and was baffled. Thats when he gave up. Listen i hope i am not being a nuisance, and i truly appreciate your help. Thanks again. Have you ever recieved any questions or info from a place called Matt's Caddy Shack in El-CAjon, San Diego Ca.? I spoke to him he said bring it and i will fix it. Who Know's I sure don't

Answer
Hi David, No I haven't recieved any questions specifically from that shop or on the same problem as yours. The only thing that I see is the name that you type in at the top of your question page or if you say you are from a shop in the  body of the letter. The B120 is a twilight sentinal problem. The B334 is a loss of data problem with the ECM. There is a service bulletin that might help but is too lengthly to explain here. Maybe he can find it on his computor at work. The number is T90-90 in group 8 or  #018112. The CPS is located above the accellerator pedal and is a smaller silver box about half the size of the ECM/BCM and has a part number that ends in 396 or 406. If it doesn't end in 406 the other CPS was known to cause the dash or displays to go blank. A bad cliamate control panel can also cause a service car soon system failure. This shouldn't cause the engine to die. I still feel that the battery cable has a bad ground and the way to test it is to set the digital volt meter on the lowest range and put one lead on the engine block near the cable and the other one on the cable near the ground bolt. With the engine running and the headlamps on high beam and the blower motor on high the reading should be less than 2 millivolts or .002 volts. If it is higher than that then the meter and leads need to be tested and if ok then the battery cable needs to be removed and cleaned like I previously stated. There is also a bulletin for that too. Sounds like this car is going to be a toughy and might require someone with more Caddy knowledge. Repost with more info and I'll try to help. Bill