just got myself a jeep and it has a few problems but the one thing i'm concerned about is a code p0135. the handbook that came with the diagnosing tool i bought says heater circuit malfunction but what generally is the cause of that problem? i dont want to start taking things apart, i'd like to have a rough idea of where i'm looking. its a 2002 jeep grand cherokee laredo.

 

Welcome to CF!

P0135 is 02 sensor heater malfunction Bank 1, sensor 1. The 02 sensors have heaters inside them to get them up to temperature quickly so they can start adjusting fuel mixture sooner. The heaters have been known to burn out or short internally and this is normal. I've had the same code on my 4.0 since December and I'll get to it before August when it needs to pass inspection. It just idles a little rough until that sensor gets hot. No big deal.