I have a 2002 Grand Prix that I recently purchased with 130K miles. It has the following issues some of which are related, others which are not: P0420 Catalytic converter code, Heat only works on setting 5, lights flicker when going through the different levels of heat/AC, rear defroster doesn't work, lights behind fuel gauge and in the radio goes out at times. I have done the following things: Checked the fuse box for the blower motor which does show the proper voltage. The resistor had already been changed prior to my purchase (I was not aware of this), I changed it with a brand new part again which made no difference. So it apparently is not the ignition switch, blower motor or resistor. The control module? Random water damage shorting parts out? There are no obvious signs of water damage.
Thanks for the reply, I'm aware of the Cat code, but I saw an issue online where someone said that code came up when they had the other issues and they were somehow all related but I don't see quite how that is possible. Cat replacement isn't cheap so going one by one with the other issue until it's solved. Usually the culprit is the resistor, and rarely the ignition switch, but both seem fine. I'll look into the blower switch.
December, 3, 2011 AT 2:19 AM
Just to add, I would look close at the connector for the resistor. They fail a lot. Replace both the resistor and the connector.
The 420 has no effect on the other issues.
Dash bulbs may be failing or the circuit board behind the dash is bad.
Check the rear window for broken wires for the rear defroster.
December, 3, 2011 AT 4:22 AM
I've read many issues where all of these symptoms occurred (minus the Cat code) and there was a fairly simple solution each time. I am going to trace all of the wires with my friend who is a retired mechanic, but I'm hoping someone will have heard of another solution for this. Is it all caused by water leaking under the hood cowl through the cabin filter? This specific car had a lot of issues with this type of thing.