I have read that you should not clear codes by unhooking the battery cable. I have also read that some places are not allowed to clear codes. If one is troubleshooting codes and trying things, what is the proper way to clear codes? Is there a problem with unhooking battery to clear them? How long does it take (mileage, hours) for codes to reappear? Will codes clear on there own if the problem is cleared up? If so, how long will it take? Sorry for so many questions but for us new guys this info would be helpful.

Thanks

 

While they claim they aren't supposed to, the guys at Advanced Auto Parts would hand me the scanner and let ME clear them- Of course, this was typically after I purchased the necessary parts, etc to fix the problem originally.

 

Or you can just get yourself a scanner at Harbor Freight for <$20. Lots of people on this forum like the Ultra Gauge which is a tool that is a scanner, but also gives you real time data about how your truck is running... particularly engine temp. As you may or may not know, the temp gauge on these is pretty worthless. Once it shows temp is going up, engine is already way overheated...

Ultra Gauge

 

Another point - write down the code numbers, don't trust the "english" translation by the generic code reader. Check numbers against RAVE text. Also, some codes will repeat right away if problem not revolved, others take 2, 4 (like P1452) "drive cycles" to make CEL pop back on. So you might clear it, and go out of town on a road warrior trip, and SWMBO will call that the light is back on two days later.

 

related question: some codes clear themselves after a bit, like in my case p0305,p0300 (misfires). I know I need to replace plugs and wires, but the light came on when I was in Canada and by the time I got back to NH (400 miles or so later) the SES light went out on its own.

Since the SES light cleared itself, would those codes later cause me to fail inspection or are they effectively gone for good?

 

Comes that come and go are light fault codes indicating that a problem is there, lights that stay on are hard faults and need to be dealt with before trying to clear any codes.
Also leave your battery cables alone, playing with them can lock out your radio, change your temp settings, clear some of your adaptive memories and not even do anything to the codes.