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1992 STS No Heat - ECM Code 048 - 039


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I own a 1992 STS and love it. I have done alot of work to it and it needs more. I know a bit about cars but i want others opinions. currently my car is giving a 048 ECM code upon start up, i have recently lost my manual and dont know what this means. It also will occasionally give a 039 which i found to be a torque converter code... It will also slip in and out of gear under heavy acceleration occasionally... not often but once a month. I have been told that is related to a solenoid going out.

The past repairs since i have had it for 2 years have included starter/ignition module/water pump/brake calipers. In some of the repairs i had to move the A/C compressor. I do HVAC work on homes so i was careful to not burst the lines and keep wires intact. When i purchased the car the a/c worked.. seemed a little low on refrigerant but not enough to keep the clutch on the comp from engaging. I dont have to drive my personal car very much, so i am not sure when this problem started .. but here is what it is doing now. The A/C wont engage..(i verified it has enough refrigerant) the controls work fine and display fine (they seem to work fine, i have not actually worked on them..) Now that it is turning colder here in alabama i have noticed my heat no longer works. I have plenty of coolant. If my heater core is stopped up would that cause my car to over heat? It runs 197F on average not exceeding 203F. Is there a damper that changes air flow from across the evaporator coil to the heater core? The other dampers appear to work .. as far as floor vents - passenger vents - defrost vents.

Any help is appreciated. I need to now where to go firts.. My main concern is the heat issue. Please help. Sorry for the typos and writing style.

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I also have a 92 STS. My heater use to blow air, but it was cold air, haha. It ended up being a clogged heater core. It is a simple procedure to fix it. Search for clogged heater core. I recently posted a thread. Now I have a bunch of heat! The fix cost be about $20. I had to refill the engine and radiator a with coolant and the Bars-Leak supplement because when I unhooked the lower heater core hose, the coolant drained out. The problem also could be with the HVAC. I would go on eBay and find a Cadillac Service Manual for a 92 STS. I have one and it explains everything in detail. There are some test you can run in diagnostics to see if the problem is with the doors. I hope this helps!

-Aaron :D

18 Year Old Male

Black 1992 STS 4.9L

90,XXX Miles

Flowmaster 80 series muffler :D

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There is an air mix door that could be stuck. It is vacuum controlled. A pluged heater core could also cause it and would not cause an overheat situation. On the 4.9 the is a "T" fitting that must have a plug with about a 5/16" orafice in one of the legs of the "T". If it is missing or in the wrong leg you won't get any heat. I do not remember which leg it is but do a search and read the post by Bbobynski. He has explained it several times. Once recently I believe.

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The T has an arrow directed to the heater core. You can watch air mix door movement if you remove the glove box ( easy). There is also a diagnostic for the airmix door search the recent archives. I have flushed my plugged core but it started keaking (bad gaskets). If it happens you can still replace the core (40-50$) it's a pretty time consuming job though not rocket science.

The saddest thing in life is wasted talent

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If the system has a proper refrigerant charge and not cooling properly as well as poor heater performance, I would suspect the mixer door as described above.

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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