Q: I own a 1997 Pontiac Grand Am GT (3.1-liter V-6) and the temperature gauge inside the car is operating erratically at temperatures above 65-degrees. When this occurs, the gauge goes back-and-forth from hot to cold and this also causes the engine to hesitate and surge. I've taken it to a couple repair shops and they can't find the problem. One repair shop replaced the coolant sensor and the problem returned about an hour later. Again, this only happens above 65-degrees and when it's colder outside, the problem does not occur. The "check engine" light did come on but no codes were stored. When I see the temperature gauge go low, I can feel the fast idle kick up. What do you think could be causing this?  --B.C., Homer Glen

A: B.C., the temperature gauge in your vehicle's instrument cluster does not utilize its own sensor, but instead gets its information from the Powertrain Control Module (PCM). The engine coolant temperature sensor, which is threaded into the engine's coolant jacket, is a variable resistor affected by engine coolant temperature and it connects directly to the PCM. The PCM needs to know engine temperature in order to control the fuel injection system, ignition system, and various other systems. The PCM sends the engine temperature information to the instrument cluster. Apparently, the temperature gauge in your instrument cluster is merely responding to what the PCM is transmitting. That could mean that there's something wrong with the PCM or its wiring. But before condemning the PCM I would carefully inspect the wiring between the engine coolant temperature sensor and the PCM. I'd also recommend inspecting all of the PCM's ground circuits, especially the sensor ground circuits. I would also monitor the coolant temperature signal directly at the PCM connector and operate the vehicle above 65-degrees. The PCM would be suspect if the coolant temperature sensor signal at the PCM remained constant while the gauge in your cluster fluctuates. Take your Grand Am to a repair shop that specializes in engine performance and drivability diagnostics.

Q: I own a 1996 Jeep Grand Cherokee. After hooking up a trailer I noticed that my license plate lights aren't working. I've checked all the fuses and can't figure out what's wrong. Do you have any ideas? -- D.O., e-mail

A: D.O., if the license plate lights are the only lamps not working, the problem could be a poor connection at one of the connectors in the rear of your vehicle. But before digging through the wiring, did you check the bulbs? Maybe they're bad. Maybe there's a problem with the ground circuit for those bulbs. If you remove the bulbs, the terminal that connects to the black wire should have good continuity to ground. The other terminal inside the socket should have battery voltage when the lights are turned on. If the ground is good and there's no power on the other terminal, it could be a problem with the lamp-outage module. Take your Jeep to a repair shop that specializes in electrical repair and they should be able to figure out what's wrong.

Questions for Ira Siegel? Call the Auto Adviser Hotline at 708/633-6839 or e-mail Autoadvisr@aol.comAutoAdviser: Ira Siegel is an Automotive Instructor and ASE Certified Master Auto Technician