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Engine Light `On' Vehicle Fails State Inspection

By Junior Damato, July 21st, 2018

strong>Dear Doctor: I have a 2005 Mercedes-Benz ML-Class with the engine light on all the time. The dealer told me it was due to a bad fuel tank cap (they tested using an EVAP leak test with smoker). The fuel tank gas cap was replaced, but the engine light remained on. Then, I was told that it was due to a leak in the charcoal canister that's part of the fuel tank; and since it's part of the fuel tank, the entire gas tank will have to be replaced. The repair will cost $4,000 to $5,000. The vehicle has 93,000 miles on it and runs OK, but will not pass the N.Y. state inspection with the engine light on. Any suggestions would be appreciated. Tirath

Manufacturer photo: 2005 Mercedes-Benz ML-Class
Manufacturer photo: 2005 Mercedes-Benz ML-Class

strong>Dear Tirath: It does sound like there's an EVAP leak in the system, which will trigger the check engine light. I see many EVAP leaks that can cost a lot of money, such as in your case with the Mercedes. In the state of Massachusetts where I reside, I have found that the EVAP monitor will not set the check engine light on when the fuel level is 3/4 full or higher. If you were to fill the fuel tank, clear the check engine light, and perform the needed drive cycle without letting the fuel tank go below the 3/4 level, then your vehicle may pass the emission test. You can ask the local smog center if the same applies in your state.

strong>Dear Doctor: I own a brand-new 2018 Cadillac CTS with the automatic start/stop technology. I don't really like it. Is there a way for me to deactivate it on this model? Anthony

strong>Dear Anthony: On some vehicles, the automatic start/stop technology cannot be shut off without a factory-equipped on/off switch. The feature turns when the transmission is shifted into the sport mode, or shifted into first gear, while others cancel with the defroster, a/c, or rear window deicer on. Have you spoken to the dealer service department? The factory GM scan tool may have the software to modify the on/off feature. Aftermarket companies are also working on downloadable software as I write this answer.

strong>Dear Doctor: I have noticed that a lot of drivers do not use their parking brake, but instead just put their car in park even on an incline. I believe that the transmission is not designed to hold a car. What are your thoughts about using the parking brake -- and should it be applied before putting the transmission into "park"? Marty

strong>Dear Marty: You are correct: the majority of drivers with automatic transmissions do not use the parking brake. In fact, the only time I use my parking brake is on a hill or boat ramp. The parking pawl in the transmission is very strong and I have yet to see one break apart. The safest way to park is to apply the parking brake after the transmission is shifted into park. Mechanical parking brake parts do freeze up from not being used, especially in the Snow Belt area where rock salt plays a big part in rust and corrosion. Some of today's new vehicles have an electronic parking brake that is part of the rear brake caliper. A push or pull of the parking brake button is that's all that is needed to put the parking brake on or off.

strong>Dear Doctor: I live in the northeast and I have a relative who lives in Florida, who advises to never completely fill up the car's fuel tank in hot weather. Would this make sense due to heat expansion in the tank? In all my years, I've never heard this advice. Is this a Florida urban legend? Tyrone

strong>Dear Tyrone: This holds true to any gas- or diesel-powered fuel tank. The expansion due to heat not only can spill out of the vent system on boats and lawn mowers, but also on passenger cars and trucks. Overfilling a late model vehicle can damage the evaporative part of emissions. The extra fuel can enter the vent solenoid and charcoal canister damaging the system that has hoses and valves that connect to the fuel tank. In the Sun Belt states -- such as Florida, Texas, and Arizona -- overfilling the fuel tank cause major problems.

strong>Dear Doctor: I'm working on my 1966 Ford Mustang and have purchased many new reproduction parts and found the quality to be very poor -- and in some cases broken in the box. Some body parts do not even line up. Any suggestions on quality reproduction parts? Steve

strong>Dear Steve: You are not alone with poor quality reproduction and it's not just Mustang-related, it's also that the majority of these parts. However, I found a company that has very good quality parts for old Fords, as well as other vehicle makes. The pricing is very reasonable, too. The company is United Pacific located in Long Beach Calif. The web address is, or call 1-888-986-6088.

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