While driving around the city in my Hummer h4T, I noticed the Check Engine light come on, so I head back home for fear of aggravating any problem with the engine. I popped up the hood to see what's going on and did not find any problem. What could possibly be causing the CEL to come on?

You should be thankful that there is nothing wrong with the engine, and you have not found any issue that could cause the CEL to illuminate. This is most probably a case of a worn or loose gas cap. This small component is responsible for sealing the fuel system. When not locked properly or when the seal is faulty, it can cause havoc and activates the Check Engine light. The light will remain on until the gas cap is sealed properly. Lucky for you, gas caps are really easy and inexpensive to replace. You just have to look for a gas cap that is right for your vehicle, place it over the fuel tank opening, and twist clockwise until it clicks into place.

I love my Hummer h4T but it's driving me nuts these past few days. The other day, I was driving it to get some groceries when it suddenly stopped; I called in a towing service and the mechanic told me I ran out of gas. But the fuel gauge is telling me I had a full tank. Sometimes it will show fuel tank empty when I just had it filled. What's going on here?

There really is nothing more annoying than having a fuel gauge that doesn't give you an accurate reading. It's more likely that you have a faulty fuel level sensor in the fuel tank, and it's causing the fuel gauge to be erratic. This is a common problem among vehicles that already have high mileage on them. Contaminated fuel is usually the common cause of fuel sensor failures. The amount of sulfur in the fuel may corrode the contracts in the sensor and cause dead spots or loss of signal. Sometimes, a bad fuel sensor is also an indication that something is wrong with the fuel pump. In fact, you may need to replace the complete fuel pump module assembly if the erratic fuel readings continue.

As a precaution, I regularly check everything in my Hummer h4T; that includes the coolant level. The other day, I noticed that my coolant level is really low, so I topped it up only to find the next day that the car is low on coolant again. I checked for leaks but there was none. What should I do?

Not all low-coolant-level cases mean there is a leak in the system. Or sometimes, there really is a leak, but it's hard to locate especially if it is going into the engine block. The only way for you to find out is to check the engine oil color and quality. If the oil is white to grey in color, then there is a possibility that the coolant is indeed leaking into the engine block. Other possible causes of low coolant but no visible leaks are bad radiator cap, bad sensor, or blocked radiator. A bad sensor can give incorrect readings and causes the warning light on the dashboard to come on, saying that you have low coolant. If a visual inspection of the cooling system reveals no external coolant leaks and you continue to get low coolant warnings, then it's time to take the vehicle to the shop for a thorough and professional assessment.

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