A Chevy dealer just replaced my computer in my 99 Silverado V8 1500 4X4. When I picked it up that evening, the Service Engine Soon (SES) light was on. I take it back the next morning and the Service Mngr scans and advised the Crank Shaft Position Sensor (CSPS) was bad. He said it was reflected in multiple data appearing on his screen (he pointed at two or three vertical locations) and the CSPS needed replacing.
I took the vehicle to friend who runs a garage and who has for years routinely worked on all my vehicles. He scanned the vehicle...his reading reflected that the computer had not completed the "re-learn" process; however, he could not turn off the SES light.
I never saw what the Service Manager was reading on his scanner, but my friend was certainly was accurate in his reading based on the code(s). By the way, my truck has run fine for probably 20 miles of driving since the SES light was first noticed.
Any ideas?