Q: The check-engine light in my 2004 Chevy Silverado 2500HD with the LB7 Duramax keeps coming on intermittently and isn't throwing any codes. I've taken it to the dealer several times, but all the techs suggest is to keep bringing it back. Could you shed any light on this situation?

A: Intermittent electronic faults can be a real project to diagnose. A shop or a technician will often avoid investing a lot of diagnostic time until the problem becomes more pronounced, or develops into a hard failure (light is always on). But it's not always that difficult. If the "malfunction indicator lamp" (check engine or service engine soon) is lighting up on the instrument panel and no diagnostic trouble code was stored in the engine control module's memory, that narrows things down quite a bit. Odds are high that the problem is the engine control module itself. You may not find this procedure in the service manual or GM digital database, but sometimes you just have to hit the thing--yes, really. The control module is located under the hood, on the left side near the battery. With the hood up, engine running, and someone in the driver's seat to observe the instrument panel, tap on the engine-control module--the black box with three electrical connectors attached--with the back end of a good-size screwdriver. If the malfunction indicator lamp comes on, or even flickers while tapping, you've found the problem. It's an internal failure and the control module needs to be replaced and the new unit reprogrammed. However, there are other possible causes. The engine-control module may still be at fault but pass the "tap test," there could be a bad connection in a major circuit going to the control module, or there could even be a short circuit within the instrument cluster. The technician should've tested for codes and other irregularities with a scan tool, done a quick tap test, and inspected a few of the control module circuit electrical connectors before sending you on your way.

Q: I have a 2005 Ram 1500 Quad Cab with the 5.7-liter Hemi. It's pretty well known that some people experience a "tick" with their Hemi. I'm one of them. I've spoken to multitudes of Dodge/Chrysler techs who all say it's normal and that a warranty repair isn't needed, yet I've read on numerous online message boards that some people have actually gotten their local Dodge dealer to admit there is a problem and get their Hemis serviced under warranty, but from what I've read it's complicated and expensive (for the dealer), which is why they don't want to admit it. Can you shed any light on this? I can't seem to get a straight answer from a dealer, at least not from anyone in my area.

A: Nothing in writing (TSBs) from Dodge on the subject, but the "Hemi tick" seems to be a common grumble from Hemi owners. I touched base with a longtime friend and Dodge technician on the East Coast regarding the engine noise. According to my guy and Dodge technical support, it's a hydraulic valve-lifter noise which is being considered a normal characteristic of the new-generation hemispherical combustion chamber (Hemi) engine. The ticking sound is typically heard from a warm engine, idling, while standing to one side of the truck--more commonly noticed bouncing off the wall at a drive-thru. The technical cause is thought to be the somewhat horizontal positioning of the hydraulic roller tappets (valve lifters) in the engine block. The lifter location projects normal lifter noise out the sides of the engine. Certain engines do tick slightly more than others. The only attempted fix I could imagine would be to replace the lifters, which may not accomplish anything, and I don't see tearing down the engine being worth the risk. I haven't heard of any claims regarding long-term durability issues involving the noise, so at this point in time, try to ignore it. If the noise is something other than described, have it checked out.