Recently, CarMD Corp. conducted a study and compiled the findings into what they called their Vehicle Health Index. CarMD is a device that plugs into your vehicle and then downloads vehicle repair data, letting you know what's wrong with your car. Among the findings of the study were the top five most common repairs you can avoid through proper maintenance.

1. Engine Misfire

Each spark-plug on your car is electrically timed to fire at precise timing to deliver power from the engine. If the spark fires at the incorrect time or not at all, it is considered a misfire. Misfiring of a cylinder can happen for numerous reasons. Here are the most common causes and related costs of the misfire condition:

• Carbon or oil fouled sparkplugs: $100 to $300 depending on cost of plugs and labor to replace. (Bear in mind that oil of carbon fouled plugs are the result of a deeper problem with the engine and to get to the bottom of such case will cost more time and money to fix).

• Bad spark-plug wires: $100 to $300 depending on cost of parts and labor to replace.

• Bad fuel delivery: $100 to $1000 depending on cause of fuel delivery problem: bad injectors, cracked intake plenum, new injector driver or flash programming of ECM (Engine Control Module) needed.

• Vacuum leak: $100 to $1000 depending on cause of vacuum leak.

• Mechanical breakdown: Broken valve spring, burnt valve, broken or burned piston or piston ring, blown cylinder head gasket. Repairs for this can run from $500 -- $10,000.

What to do? The best way to avoid an engine misfire condition is through following the scheduled maintenance in your manual. Keep your vehicle's engine tuned according to factory specs. Plus, a yearly trouble-code scan by a well-equipped shop will uncover any potential problems before they become major faults.

2. Evaporative Emissions Leak and/or Failure

The evaporative emissions system control (EVAP) system is designed to trap gas tank fumes. The system consists of the fuel tank, vapor lines, liquid vapor separator to prevent liquid gasoline from entering the system and the EVAP Canister, which has a purge valve on it. Fumes are trapped inside the canister, which is full of activated carbon. At certain times during engine operation, the canister purge valve opens up letting fresh air into the canister. This in turn forces the trapped gas fumes back into the engine's air intake and thus burned inside the engine.

Should the system develop a leak as a result of corrosion eating the lines or a compromised canister, the system will throw an "EVAP Leak" code in the computer. To fix the problem, one has to find the leak, or faulty component, fix or replace it, and reset the system. The whole process of diagnosis and repair typically runs anywhere from $100 to $700 depending on what's needed.

What do do? To keep EVAP Systems operation properly, always make sure you tightly re-install your gas cap after refueling. In addition, a good rust protection application helps to keep system line corrosion to a minimum. Always tend to lit check engine lights. If you let them go, an EVAP System problem can expand into major repair costs.

3. System Running Too Lean

If a "System Too Lean" code comes up, it's usually due to a vacuum leak, faulty injector driver, bad injector or a software update needed. The performance computer monitors engine operating elements such as coolant and air intake temperatures, amount of airflow into the engine, throttle position, etc. If the problem-code pops up, it's because one of these areas is compromised. The mechanic must scan the system, identify where the malfunction exists and repair it. Typical causes of lean conditions range from a bad vacuum line, faulty sensor, broken engine gasket to a cracked cylinder head, faulty intake plenum, warped throttle body, and too much more to mention here.

Repairs run anywhere from $150 and up because it can be as simple as a sensor replacement or wiring repair, but it could also be a major engine repair costing thousands.

What To Do? Regular maintenance and upkeep will avert these type of problems. Always tend to a lit check engine light because we don't want a small problem to snowball. Don't be penny wise and pound foolish when it comes to preventive maintenance.

4. Catalytic Converter Failure

Catalytic Converters fail for two reasons: either because of a leak from rust and corrosion setting in, or internal plugging from excessive carbon buildup or collapsed baffle or catalyst. The catalytic converter is a device that burns up any unburned gas in the engine exhaust, cleaning the tailpipe emissions. Problems crop up when more unburned gas is fed into the catalytic than it can process. For lack of a better term, the catalytic becomes "constipated" or clogged as a result of too much gas being fed into it. The clog takes the form of a "rock" of carbon that forms inside the cat, causing a restriction of exhaust gas flow.

The only way to restore the system to proper operation is to replace the catalytic converter. Now this is where most people stop the repair process. But then the new catalytic comes up with the same problem just a few months later. Why? Because the tech did not get to the bottom of the problem the first time. The reason the catalytic clogged was probably because there was uncontrolled fuel delivery. Make sure your mechanic gets to the root cause of the unchecked fuel delivery before paying the bill and driving away.

What to do? To avoid catalytic converter problems, keep the your engine up to snuff with regular scheduled maintenance tune-ups and system maintenance as per factory recommendations in your manual. It's really the only way to prevent premature failure of the system.

5. Exhaust Gas Recirculation (EGR) System Failure

EGR stands for Exhaust Gas Recirculation. This is an emissions system designed to lower combustion chamber temperatures in order to lower formation of NOx (Oxides of Nitrogen) gas, which contributes to harmful air pollutants.

Because of the system's very nature (feeding exhaust gas), it is highly susceptible to carbon (unburned gas) buildup, plus electronic control problems. EGR Valve complications arise from wear of the valve over time. Typical repairs include valve replacement, sensor or controller replacement, or wiring repair.

Repairs can run anywhere from $200 for an EGR tube replacement, to a valve replacement, while EGR passage cleaning costs about $700. Repair costs vary by year, make and model.

What to do? To keep your EGR system functioning properly, have a professional fuel system cleaning done every 30K miles. This will keep carbon buildup, the EGR systems greatest enemy, at bay. Attend to any check engine lights immediately.