bcresc

OK.. I stopped working on cars when they still had carburators... My check engine light just came on and I went through the codes. Tons of A0-LDCM codes with history designation, and A1-RDCM with the same. I am also getting 10-PCM Codes P0171 HC P0174 HC, which I gather has something to do with fuel trim being lean. WHERE DO I START? Is there something obvious that I should be looking for, our should I be heading for my Chevy dealer? Any help is greatly appreciated. By the way, it is a '99 C5.
Thanks,
Bob

Chris@East Coast Supercharging

On the lean status.. have you recenty done any mods to the car?

bcresc

Hi Chris:
No, I have not touched the car. It's completely stock with 22K miles on it.
Thanks,
Bob

knkayotte

I'd clear the codes and see if they come back. Could of been a fluke.

Later, Keith

bcresc

Keith:
I did clear them. The PCM codes returned after driving about 15 miles.
Thanks,
Bob

CDHough

You can get those codes for a variety of reasons. Air leaks letting air in between the MAF and the engine is possible. I also believe that fuel delivery problems can cause the code (clogged or blocked injectors). My service manuals are at home, otherwise I would give you the details. I would go to the dealer if you haven't changed anything on the car. Good luck.

- Charley

bcresc

Thanks Charlie, If all else fails, I have an appointment with my local Chevy dealer this Thursday.
Bob

Halltech

Bob, these are called lean codes, banks 1 and 2. They result from turbulence at the MAF wire, or unreported air leaking behind the MAF wires at a connection or cracked bridge.

Some MAFs with the laminar screen removed do a poor job of reporting the mass of air to the PCM. When the O2s (rear guard) sees the leftover O2, it reports that as new air, which the PCM adds fuel to compesate back to 14.7:1 a/f ratio.

The Delta between MAF reported air, and actual air after the combustion process, which goes beyond PCM authority will cause this code to pop.

Generally these codes will not hurt your motor, but should be looked into right away.

Jim Hall

bcresc

Thanks Jim... Is there anything the "non-wrenching" owner can look for to confirm that the problem is with the MAF?
Bob

bcresc

Hey Guys. Thanks to all. I did find an air leak between the air duct and the throttle body. It was separated on the bottom, out of sight. Hooked it back up, cleared the codes and drove the heck out of it. So far, no new codes and the check engine light is still out (yes I am knocking on wood right now).
Thanks again!
Bob