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Chrysler Corporation (including Dodge and Plymouth) vehicles with fuel injection, like all current computer-controlled vehicles, watch their own behavior and set "error codes" when they see something which is not as it should be. Computers only do what you tell them, so they might not see problems which do exist, or they might see problems that do not exist, or they might indicate a problem which is in reality caused by some other component. They work is by checking their inputs against each other - for example, if the voltage coming from the oxygen sensor is not what it expects given where the throttle is, how fast the engine is moving, etc., it will post an error code and, in some cases, light up a warning lamp on the instrument panel.
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Dealers have sophisticated computers which plug into your car's computer and can gain massive amounts of information; but backyard mechanics can also benefit from knowing what the computer thinks is wrong (since it's often right), especially given that those well-equipped dealers often have dishonest and poorly-trained mechanics.
Please read all the bullets before zooming to the codes. Thanks.
Instructions and codes
Instructions and codes
You may want to invest in an OBD compatible code reader. They're inexpensive and some can record sensor readings and save them to a file, making diagnosis easier. This is the code list. That said, many Chrysler cars, vans, and trucks will show you codes without any readers.
The computer will eventually reset itself; you can also use a scan tool. (See our transmission repair page for information on resetting the computer's transmission information.) Disconnecting the battery for a few minutes resets the computer, but loses clock and other settings.
Sid Willoughby wrote: “To clear the check engine light on a 2002 Dodge Ram once the problem is resolved. Start the engine and drive forward then in reverse (you only have to move the truck a few feet in each direction) the turn the ignition off. Do this sequence three times. When you start the vehicle the fourth time the check engine light should go out.” (This procedure may work on other vehicles.)
You can find out by trial and error which list is right for you. The older codes were two digits; the newer codes start with a P and have more digits.
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computer fault codes: how to get them and what to do with them. Good
for sensor and other troubleshooting.