Another kind of extended warranty

If your new car warranty has expired, a common belief is that you can save money on repairs and maintenance by finding a good independent mechanic, avoiding the dealership service department.

Though often true, that common belief sometimes has its faults. A simple example involves special extended warranty programs offered by car manufacturers to cover defective parts.

Dealerships know all about these goodwill programs, but independent shops sometimes do not. As a result, you can end up paying for a repair that would be fully covered by the manufacturer.

Among the very largest of these extended warranty programs is one currently offered by Ford Motor Co. on an emission control device used on millions of vehicles produced between 2000 and 2002, including its big selling F-100 pickup truck and its Taurus passenger car. It is a good case study of the issue.

The part is known by the unwieldy name “tube mounted exhaust gas recirculation pressure sensor.” It is part of the emission control system that sends a small percentage of exhaust gas back into the engine’s combustion chamber to help improve the burning of fuel and reduce emissions.

Under Ford’s original warranty program for cars sold in California, the part was covered for three years or 50,000 miles. Under the extended warranty program, it is covered for five years or 74,000 miles. So, the extended warranty is covering cars at an age when most owners aren’t thinking they have warranty coverage.

When Ford discovered a problem, it sent out letters notifying dealers. Ford mechanics know all about the program. Almost every dealership has replaced hundreds of these sensors.

Ford also sent out letters to owners, though such notifications often fail to reach individuals who move or who are second owners -- or they can simply get tossed aside.

If the part is tricky to understand, diagnosing the problem can also have its pitfalls. In a few vehicles, the defect can cause hesitation, engine surging or stalling on start-up, according to a Ford letter to dealers in June 2004, which was republished by Alldata, a car-repair information service.

Not to worry, says Ford. “None of these conditions will cause engine damage or failure, but they may decrease the customer’s satisfaction with their vehicle,” the letter says. It’s so nice of Ford to think about customer satisfaction.

In most cases, the only warning of the problem and the only way to diagnose it comes from the check-engine light on the dashboard. The check-engine light is part of a diagnostic system on every car. With a code reader, a mechanic can extract various engine problem codes.

In this case, the system would report one of four codes, such as a P1400, indicating the sensor is reporting a low voltage.

The other error codes would warn of other problems, such as excessive or insufficient exhaust flow past the sensor.

So, if the dealership mechanic gets one of the four engine trouble codes indicated in Ford’s extended warranty program, you get a free sensor. End of story? Not really.

In some cases, a car’s diagnostic system will not report one of the four error codes, but some other problem. In some cases, it will report that there is an oxygen sensor malfunction. Why? Because the diagnostic system finds excessive emissions and wrongly thinks the problem is being created by oxygen sensors.

These oxygen sensors can cost hundreds of dollars to replace. This is not a theoretical issue, but a common problem with diagnostic systems.

In the worst of all worlds, an independent mechanic would replace the oxygen sensors and the owner would still have a defective exhaust gas recirculation sensor, which would probably later cause a new error code.

What are the lessons here? Independent shops can be fine, but if you use one make sure it subscribes to a service that publishes all the recall notices, technical service bulletins and other information commonly available to dealership mechanics. Alldata and Mitchell Repair Online are two major publishers of such information.

Second, with a little hands-on effort, a smart car owner can save lots of money. If you are capable of taking care of a home computer, you are probably technically adept enough to pay attention to your car’s diagnostic system.

For about $100, you can buy a trouble code reader and extract codes -- just as the mechanic did with the check-engine light. The code readers plug into the car’s computer through a socket under the steering wheel. You don’t even have to get your hands greasy.

Third, for a small fee, you can buy the technical service bulletins for your car. These bulletins are available online for an annual fee from Alldata (www.alldata.com). I don’t know of any other service that provides them.

Free summaries of technical service bulletins are also available from the National Highway Traffic Safety Administration at www.nhtsa.dot.gov/cars/problems. But its search engine leaves a lot to be desired. For example, it failed to list the Ford technical service bulletin on the defective sensor.

Finally, there are many good independent mechanics and good dealerships. It makes perfect sense to shop around and figure out what kind of service works best for you.

Ralph Vartabedian can be reached at ralph.vatabedian@latimes.com.