WayneSS01

The light came on yesterday afternoon soon after topping off the gas tank. I gave the gas cap three clicks when tightening it. Meanwhile the engine had a miss. The plug wire on #5 was loose, fixed that and got rid of the miss. But the SES light stayed on while driving around last night.

This morning the light came on at start up. Less than 2 miles from home it went off.

The car was at the dealer for an SES light. They found code P0130 'H021 Circuit Sensor 1' and replaced the 'AIR Pump Vacuum Valve'. It's located above cylinder 7.

What's up? Why does the light go off on its own? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

CMNTMXR57

That's not uncommon after filling up with fuel. It's particularly common on FWD GM cars.

It is a pending DTC and will clear itself after three successful operating cylces AFTER the cycle that originated the code.

The random misfire code P0300 and P0305 (for cylinder #5) if they were thrown, would also clear after the same 3 successful operating cycles.

I wouldn't worry about it.

<small>[ March 25, 2003, 11:26 AM: Message edited by: CMNTMXR57 ]</small>

WayneSS01

Thanks. So far the light is still off. I was not aware the light would 'shut itself off'. Thought the codes had to be cleared or the problem addressed before the SES would go off. Learning is fun. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

WayneSS01

Wow, this is good stuff. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

A dyno operator once told me it is good to re-set the PCM about every oil change. He said it was like re-booting a PC. He described the method I've seen on the boards. Any truth to that?

1. Turn key on but don't start car.
2. Pull PCM BAT and PCM IGN fuses in engine compartment.
3. Wait a few minutes.
4. Turn ignition off.
5. Replace fuses.

CMNTMXR57

That's an "idle Re-learn" and another way to shut the SES light off if you don't have a scanner to do so.

I dunno if I'd recommend doing it every oil change though! Part of it is allowing the PCM to learn your driving style. Why constantly reset it to re-learn it (as well as the idle) over again?

WayneSS01

Ok that makes sense not re-setting it regularly as mentioned. I did however re-set the PCM when I first got the SES light in late Dec. Three weeks later it came back. A friend atapped the car and then cleared code P1416. That lasted for two months so this time I took it to the dealer. They got code P0130 and did the valve replacement.

I have definitely learned some PCM stuff here. Thanks! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> Maybe one day I'll mess with a MAF translator or even LS1Edit. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

CMNTMXR57

Well, yes and no. There are two types of codes that the car can throw.

1 is a DTC (Diagnostic Trouble Code) which will trigger the MIL (Malfunction Indicator Light) or in common speak, the SES light. The DTC depending on what it is, will more than likely need to be physically cleared via Auto-Tap, EFI Live, or a GM Tech2 scanner. They most commonly will clear themselves out and turn off the SES light on their own. However, that usually clears after 40 successful operating cycles AFTER the system pass a system test (for that DTC). So even if it was a once in a lifetime thing, it'll be quite awhile before it clears. Let alone those that it will repeatedly and intermittently generate the code. In that case the light would never go off. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

2 is called a "Pending DTC" These are potential DTC's that "could" be set in the future or could be a domino like effect from a regular DTC. Or simply just a pending non-essential random code. These codes (as well as some DTC's in #1 above) will clear after 3 successful operating cycles after the initial failed cycle. Pendings can also be cleared via a scanner listed in #1.

All in all, some regular DTC's, will clear also after three successful operating cycles after the failed cycle. It depends on what the code is.