Have a 2001 Chevy Silverado 4.8 with only 230'000 miles. It had a check engine light. looked up the code made the repair. disconnected the battery to clear the code. Now it runs all modules but doesn't clear but one of them. If you reset the code reader again it read within 100 miles all codes but one. This last code it won't read is a different one each time. Do I have a CPU memory problem or is it a question of driving more miles?