Trouble codes

[MN6WS6]

I have a Carchip E/X and I did a little scan of the Firebird the other day and came up with some codes. Now of course, being a GM, one of them is the EGR system, as I have never owned a GM that didn't throw an EGR code at some time in it's lifetime. Anyway, here they are, and the Carchip definitions:

P0300 Random/Multiple Cylinder Misfire
P0400 Exhaust Gas Recirculation Flow
P1641 Unknown Powertrain DTC

Now the P0400 has been in there for a while, I've cleared it out, and it keeps coming back up, and we don't have inspections or emissions testing here so I don't worry about it.

The P1641 I've never researched to find out what it is, but it has come up in the past too. The reverse lamp switch is bad in the car, as the backup lights have only worked a couple of times, and only if you got the shifter in a certain position. The bulbs are fine, I've energized the circuit and they light up, so I know it's the switch. I don't know if this code has anything to do with that, or if possibly it could be my skip shift module has taken a dump, either way, neither one of those two things bother me. But I would like to know what specifically this code has to deal with.

The P0300 is new. I've had this scanner on the car while it's been in the shop at my work to see if anything pops up (like a tech hot rodding the car). I don't drive the car much, so I put this in the morning I took it to work so I could monitor this, which means that this code popped up before it was ever touched, so I know the shop had nothing to do with it. I just had the plugs changed out yesterday, so I'm thinking if I clear the code, it will go away.

I'm just wondering what you guys think these things are and whether they are worth concerning myself over. I'm about to go on a long road trip, so if something needs to be taken care of, let me know. Like I said though, the first two have been in there in the past, so I'm not nearly as concerned about them as I am about the misfire.

[RAF7789]

i think the clogged EGR can parasite on your performance. I had that code one time, it was a PITA when i took off the EGR valve itself. i needed to use a mirror, 2 hours and some Power B'laster. the code was gone after that.

[Injuneer]

P0400 sets when the PCM cycles the EGR valve, and doesn't see the expected change in manifold absolute pressure. This can be caused by a plugged passage, broken EGR valve, leaking vacuum lines, stuck EGR vacuum solenoid, or even a low back-pressure exhaust. Removing the valve or any of the components is the sure way to set the code on an OBD-II PCM.

P1641 is for the primary cooling fan relay circuit. You need to use the correct list for an LT1. As usual, the best source for the info is on Shoebox's website. I can't believe LT1 owners either don't know about it, or don't bother to check it out when they have a problem.

http://shbox.com/1/4th_gen_tech1.html

http://shbox.com/1/Dtcs.htm

You have to check the cooling fan circuits.

P0300 sets when the PCM detects misfires, in a relatively random pattern. If you have access to an OBD-II scanner with "GM enhanced parameters" capability, you can access the misfire counts by individual cylinder, which should point you in the correct direction. Might be time for new plugs, wires, injector cleaning, are any large number of problems that can cause misfires and rob you of power. Misfires typically cause the engine to run excessively rich, and that's not good for the engine or your wallet.

[MN6WS6]

Thanks, Fred, that was the info I was looking for. I've heard of shoebox, but didn't have a link to his site, nor did I think to look for it.

The P1641 just explained itself, as that is the circuit that I have my fan activation switch run to when I'm sitting in the staging lanes at the track.

The P0400 has been on for a long time, but of course on a 80,000 mile car that's to be expected. I would bypass the EGR altogether, but I don't have LT1edit or any other way to delete it from the system. Not to mention it has the "modified cats" system in place, with 2 Dynomax bullets for mufflers on an SLP loudmouth, so back pressure has been significantly decreased.

I will have to work on the P0300 one though. I just had plugs put in (code was on before that was done), and I just cleared the codes today so I'll see if it fixed it when I get back home. If that's not it, I'm going to check vaccuum lines and probably get an injector service done here at work. If it's still there after that, then I'll have to see if I can get a hookup at the GM dealer in town so they can narrow it down for me.

Thanks again.

[Joe 1320]

I will have to work on the P0300 one though. I just had plugs put in (code was on before that was done), and I just cleared the codes today so I'll see if it fixed it when I get back home. If that's not it, I'm going to check vaccuum lines and probably get an injector service done here at work. If it's still there after that, then I'll have to see if I can get a hookup at the GM dealer in town so they can narrow it down for me.

Thanks again.

I've seen the metal spark plug boot covers cause arcing and subsequent misfire codes. I ended up having to remove mine, I replaced them with Taylor Firesleeves to cure the problem.

[RAF7789]

i had the p0300 code yesterday.... more specifically p0307, took off the boot and plug 7 to see if it was fouled at all, and it looked spankin new! so i plugged everything back in and the code was miraculously gone!! i was thinking maybe the plug wasn't in all the way to start.