Letters: Trouble codes offer clue to illuminated engine light

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Q: I own a 1998 Mercury Sable with only 63,000 miles. I purchased it from my mother-in-law, who rarely drove it. I’ve had a lot of work done to it but the check engine light is on.

I took it in for service and the mechanic couldn’t find anything wrong. He said to just drive it with the check engine light on. I don’t know if he knows what he’s doing but the car drives OK.

The only problems are the check engine light and a burning smell (like burning oil). The burning smell appears to be coming from the engine but I don’t see any oil leaks and the oil level is fine. Do you have any ideas? – Dave, e-mail

A: Usually when the check engine light illuminates a technician can read the diagnostic trouble codes (DTCs) with a scan tool plugged into the diagnostic link connector (DLC). If the check engine light is staying on and the scan tool reveals no codes, something could be wrong with the circuit to the check engine light or the powertrain control module (PCM) could be at fault.

If the scan tool doesn’t establish communication with the PCM, then there could be something wrong with the scan tool, the PCM or the circuits between the scan tool and the PCM. Sounds like you need to take your car someplace else to see if any DTCs can be retrieved from the PCM. Some auto parts stores will do this for free.

As for the burning smell, it could be that oil is seeping out of the valve cover gaskets and finding its way onto the exhaust manifolds. A closer inspection should reveal the source of the smell.

Q: I own a 2010 Chevrolet Traverse. The battery completely drained after letting it sit for about four days. I took it back to the dealer and the mechanics did a bunch of tests. They could not find anything wrong. What do you think could have caused this to happen? – Rick, Chicago

A: When a vehicle sits without being used, the battery can become discharged over time if an electrical load is staying on or if there is an excessive drain (also known as parasitic drain). Some parasitic drain is normal as the memory circuits in various computer modules draw a small amount of current to maintain memory. As long as the parasitic drain is low (under 50 milliamps), the battery should retain enough power for starting even if the vehicle is not used for long periods of time. If the parasitic drain is too high, the source will need to be determined.

There is a service bulletin that may apply to your vehicle. Bulletin 09-06-03-002G says that the instrument panel cluster (IPC) could remain energized too long after the engine is turned off, causing excessive drain on the battery. The fix involves reprogramming the IPC. Return to the dealer with this information to see if your vehicle’s IPC needs to be reprogrammed.

Q: I own a 2006 Jaguar S-Type. The problem is that when I’m stopped at a light the engine shakes the whole car. Do you know what could be wrong? – Helen, Shorewood

A: If the car has adequate power then the fuel and ignition systems are likely OK. It could be a broken vacuum hose or contaminated throttle housing that needs to be cleaned. Take it in for an inspection and have it checked for trouble codes, too.

Questions for Ira Siegel? Call the Auto Advisor Hotline at (708) 633-6839 or e-mail autoadvisor.irasiegel@gmail.com. Siegel is an automotive instructor and an automotive service excellence-certified master auto technician.