This is where a "limp home mode" comes into play. Whenever the vehicle computer gets a reading from a sensor that is obviously wrong, it will "assume" a value that it "knows will work". On the earliest computer controlled cars with feedback carburetors, if the computer got bad readings from sensors, it would run the carb at the richest setting. You would get horrible gas mileage, but the car WOULD run. The computer would then turn on an amber CHECK ENGINE LIGHT It would also store a trouble code in its memory telling what sensor was giving a "bogus" reading.
A newer car computer is much more sophisticated, and just because a "CHECK ENGINE" light comes on doesn't really mean the computer is totally in a "limp home mode". Depending on what sensor reading is out of specs the computer may still be doing a pretty good job of controlling the engine. For example, some cars can have the "CHECK ENGINE" light come on if you don't tighten your gas cap tight enough after filling up!
On most vehicles the CHECK ENGINE LIGHT will go out if the sensor starts giving normal readings again, although some computers will make you use a scan tool to turn the light off.
This is where a "limp home mode" comes into play. Whenever the vehicle computer gets a reading from a sensor that is obviously wrong, it will "assume" a value that it "knows will work". On the earliest computer controlled cars with feedback carburetors, if the computer got bad readings from sensors, it would run the carb at the richest setting. You would get horrible gas mileage, but the car WOULD run. The computer would then turn on an amber CHECK ENGINE LIGHT It would also store a trouble code in its memory telling what sensor was giving a "bogus" reading.A newer car computer is much more sophisticated, and just because a "CHECK ENGINE" light comes on doesn't really mean the computer is totally in a "limp home mode". Depending on what sensor reading is out of specs the computer may still be doing a pretty good job of controlling the engine. For example, some cars can have the "CHECK ENGINE" light come on if you don't tighten your gas cap tight enough after filling up!On most vehicles the CHECK ENGINE LIGHT will go out if the sensor starts giving normal readings again, although some computers will make you use a scan tool to turn the light off.
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