Q: We own a 2004 Chevy Impala, which occasionally gives us a problem with the speedometer. We will be driving along and all of a sudden the speedometer will stop working. Then a few hours later or the next morning, the speedometer will work fine. Have you any idea as to why this happens? Also, we enjoy your column and have learned some things from reading it. – D.T., Orland Park

A: I’m glad you have learned some things from reading my column. As for your Impala, you should know that your Impala’s speed is displayed through the instrument panel cluster based on information the cluster gets from either the powertrain control module or the electronic brake control module. The three are linked via a network. If the cluster loses communication with either of the modules, it will default to displaying 0 mph. Apparently, there’s either a problem with the electrical connection to the instrument panel cluster or the cluster itself is faulty. You’ll need to take your Impala to the dealer or a shop that is familiar with diagnosing electrical problems of this nature.

Q: I have a problem with my 2001 Olds Aurora (best car I have owned). The problem started last Thanksgiving when taking off from a stop on a cold slippery day. The front wheels spun slightly and then caught dry pavement. At that moment the check engine light came on. It is still on today. I took the car to the dealer to have the computer reset, however, by the time I drove home the check engine light came back on. The dealer said the light came on because of a problem inside the transmission and would require removal of the transmission to make the repairs. That’s very expensive and the car runs beautifully with no shifting problems. Recently I took my Aurora to an independent shop and had the transmission flushed and the filter replaced. I was told the computer code said sludge in the trans may have caused the check engine light to come on. I called General Motors and the person on the phone was apparently reading from a script and offered little help. I took my Aurora to a second dealer and was told the shift solenoids should be given an ohm’s test. The dealer said if the solenoids test OK, the problem is likely in the computer. Can you make a good suggestion that I can follow up on and take care of this nuisance problem? My car will not pass the Illinois emissions test because of the check engine light. – J.R., Chicago

A: The only code associated with the quality of the transmission fluid in your Aurora is a P1868. While this code is set when it’s time to change the transmission fluid, it does not affect emissions and therefore does not cause the check engine light to illuminate. I recommend that you take your Aurora to a shop that specializes in fixing emissions related failures. The Illinois Air Team has a Web site (www.epa.state.il.us/air/vim/reportcard.html) that rates repair shops and also lets you search by zip code.

Ira Siegel is an automotive instructor and an automotive service excellence certified master auto technician. If you have auto-related questions for Siegel, you can leave queries at the Auto Adviser hotline, (708) 633-6839, or e-mail a question to autoadvisr@aol.com.