RPO codes

theplayer · February 24, 2006

I have a 2003 Z71 Silverado. The RPO codes in the glove box show Z71 so I know its not a poser. I bought it used and it had 265/75/16 firestone wilderness tires on the stock 16"*7" wheels. I checked and the spare is a 245/75/16 so I checked the RPO codes and they show PY2 and QBX for wheels and tires. This means 16"*6.5" and 245/75/16 tires per the codes. I thought all Z71 came with 265/75/16 but my RPO codes show different. The vin sticker on the drivers door also shows 245/75/16 size for the tires, so I guess someone put these bigger tires on it before me. The codes show what the truck had on it when it left the factory right? Does this also mean my PCM is programmed for 245/75/16? That would probably explain why I am getting mileages of 13.5 in town. I am actually going more miles than the odometer shows.

05Quadrasteer · February 24, 2006

You are correct in your assumption. If the codes show the smaller then that is what your PCM is programmed for.

Here is a link that you can use to figure out exactly how much of a difference you have between the original tires and the tires you are running; http://www.fullsizechevy.com/forums/showthread.php?t=146490

Have a nice day.

Bill

redvett · February 24, 2006

I have a 2003 Z71 Silverado. The RPO codes in the glove box show Z71 so I know its not a poser. I bought it used and it had 265/75/16 firestone wilderness tires on the stock 16"*7" wheels. I checked and the spare is a 245/75/16 so I checked the RPO codes and they show PY2 and QBX for wheels and tires. This means 16"*6.5" and 245/75/16 tires per the codes. I thought all Z71 came with 265/75/16 but my RPO codes show different. The vin sticker on the drivers door also shows 245/75/16 size for the tires, so I guess someone put these bigger tires on it before me. The codes show what the truck had on it when it left the factory right? Does this also mean my PCM is programmed for 245/75/16? That would probably explain why I am getting mileages of 13.5 in town. I am actually going more miles than the odometer shows.

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Yes your PCM is calibrated for the 245's unless the owner that put on bigger tires had changes made. Not only is your speedo wrong but your PCM cals hurt fuel economy, ABS, SDM functions also.