Chrysler Repair: dash problem: 01 PT Cruiser

Question
QUESTION: Hello Roland
I have a 2001 pt cruiser that I'm having a instrument cluster problem, when I turn the lights on the gauges lose power and all the warning lights come on and it says (no bus) in OD. If I turn the lights on and off real quick then everything comes back. I have changed the combo switch with a new one and that didn't fix it also I pulled the dash out and checked power and grounds with the lights on and had both. Following the wiring diagram I see there is a CB in the light circuit and a relay but don't know if this has anything to do with this. The car runs fine this happen when the battery was installed backwards. I read one of the questions you answered about fuse #12 blowing that I was able to fix by unplugging the interlock switch to keep the fuse from blowing. Your info is very good and explains things in detail. I would appreciate any info you can give me on this issue.

 Thank you
  Gary

ANSWER: Hi Gary,
The cluster is of course a complex electronic device. I suspect it may have been damaged when the battery was installed backwards. The gauges and warning lights are all based upon the PCI digital communication bus and so when the bus communication is lost, you get "no bus". I can't explain why turning on the headlights would cause this to happen, not why turning on-off quickly corrects the problem. It may be related to the voltage on the system dropping down when the headlamps are activated. You might take a look at the battery voltage change that occurs when you turn on the lamps as the starting point for an understanding. If the vehicle operates normally other than for the cluster, then the problem is likely centered in the cluster. If you could get access to a diagnostic readout box which is capable of accessing the bus, you might get a specific trouble code which I can then look up in the body diagnostic procedures manual that I have for the '02 model, which likely applies to your '01.
Roland

---------- FOLLOW-UP ----------

QUESTION: Okay I will check the ref voltage. I think it was like 11.39v at the cluster if I remember I will check again, I have a modis scanner I was able to get into the computer thru OBII global but not the normal way as the scanner auto checks for the Chrysler ...And there where no codes at that time but P1490 and P1495 which had to do with the fuse #12 blown which was powering the rad fan relay..

ANSWER: Yes, check pin 4 which is there all the time, pin 14 when the key is in the run position, and  pin 3 which comes from the headlight switch, to see how the voltage compares when the headlights are off vs. when first turned on and when you have 'corrected' the problem.

---------- FOLLOW-UP ----------

QUESTION: Hello Roland
 Okay so I checked those points of power and had power at all of them at the times they were suppose to all were good but I had a little lower voltage at the light switch like .5 of a volt. When I did plug instrument panel back in nothing worked on the dash. Probably dash I'm not holding you to it but what do you think you have been the most helpful person on this sight and I will give great praise's on the board and will diffidently put you for tech of the month. thanks again for all your help Roland the world needs more of your kind!!!

 Thanks
  Gary

Answer
Hi Gary,
A couple of more things to check:
The PCI bus connection at pin 26 of the cluster should be verified to be connected with pin 2 of the data link connector under the dash (where the diagnostic readout box is to be connected). Also verify that pins 1 and 2 of the cluster are grounded at center rear of the instrument panel (or any other chassis metal). It those prove out, then there is something wrong inside the cluster circuitry but finding it would be a challenge. You could look over the board to see if you see any leaky capacitors.
Thanks for the rating/nomination/kind remarks.
Roland