Engine Light on

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My engine light is on in my 2003 Ford Windstar. Autozone ran a diagnostic, and suggested replacing the Mass Air Flow Sensor. I did this, but the engine light is still illuminated. Do I need to do something else to reset?

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Friday, July 1st, 2011 AT 3:57 AM

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Fault codes don't tell you which part to replace. While it's true the part is usually the culprit, the code is only intended to identify the circuit or system with the problem. That is the circuit that is supposed to be diagnosed further. The simple problems could include corroded electrical connector pins anywhere in the wiring harness or at the sensor, or a wire rubbed through the insulation and grounding out on the body sheet metal. More complex problems could include a leak in the fresh air tube, a vacuum leak, or anything else that makes it report a value of air flow different than what the Engine Computer expects to see based on other sensor data. You really need a scanner to view live data to see what the MAF sensor is reporting.

It's also possible the new sensor is working properly and the fault just needs to be erased. The Check Engine light acts differently according to the severity of the code. The mass air flow sensor is critical to all cars except Chrysler products. It has the biggest say in how much fuel enters the engine so it has the most effect on tail pipe emissions. That means anything related to that sensor is likely to be a "latching" code. That's one that turns the Check Engine light on anytime you run the engine, even if the problem is intermittent and currently not acting up, or if the problem has been solved. On most cars, those codes will erase automatically after a certain number of starts if the problem doesn't come back.

I am not recommending this but codes can generally be erased by disconnecting the battery for a minute or two. DO THAT AT YOUR OWN RISK, not because I told you to. Many newer cars have multiple computers that will lock up when the battery is disconnected or run dead. Volkswagens, for example, WILL require the vehicle to be towed to the dealer. It may not start, it will not come out of park, and the engine speed won't increase when you press the accelerator. Quite the money-making design! At a minimum, fuel trim data will be lost from your Engine Computer. You will not likely even notice that since the data is updated as soon as you start driving again.

The best way to erase the codes is with the scanner. Some of the less advanced code readers the parts stores use can erase codes as well as read them, but any scanner that can read live sensor data can erase codes too.

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Friday, July 1st, 2011 AT 7:32 AM

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