1992 gmc started showing the service engine soon light?

[AlfonsoE]

i just bought this truck 2 days ago and started showing the service engine soon light. It only comes on after driving for a while at highway speeds. but when i shut it off and turn it back on it goes away. And the oil presure gauge keeps droping on red lights (around 25p) but when i drive go back to (60p) but sometimes it passes it. is that normal?

 

[MadJack]

I suspect the oil pressure and Check Engine light is unrelated.

This vehicle was built before 1996 and will have an OBD1 computer. It takes a different GM only code scanner. Most major automotive parts stores can extract the diagnostic codes from the computer for free. However you may have problems finding a store with a code scanner for an old OBD1 computer.

The oil pressure gauge. 25 PSI is a little low but not too low. I would not consider this a problem unless the oil pressure got below 15 PSI at idle and below 30 PSI on the highway.