All recent Chrysler vehicles equipped with electronic fuel injection have a self test built in which will automatically detect and diagnose certain problems.
On some vehicles, reading the engine diagnostic codes requires a special code reader or a jumper wire. On all Chrysler vehicles I know of, no special tools are required.
An idiot light on the dash, labelled "Check Engine", "Limited", or "Power Loss" (what the hell were they thinking?) will be lit if a fault is detected. If a critical sensor cannot be read, the car will attempt to switch into a "limp-in" mode that uses preset values for the injection and spark timing (among other things).
To read the codes out of the computer on some cars, all you need is your ignition key! Without turning the key to start, flip it ON, OFF, ON, OFF, and ON within five seconds. Now watch the idiot light, and be ready to write down the codes.
Note: A loose gas cap (while the engine is running) will set a fault code! If the Check Engine light comes on just after refueling, check to see that you got it screwed in right (or, prepare to retrace your path and find out where it just fell off beside the road after you left it on your trunk lid -- oops!)
If there are none stored, you should get five blinks, a pause, and five more blinks (code 55). This indicates the end of the code list.
The exact codes vary by model, as many sensors and other systems differ from vehicle to vehicle. Fortunately, a lot of the listings are posted online. Consult the great Google with a search string such as "Dodge Spirit fault codes", and you should find a list.
Some vehicles have a slightly different method of reading the fault codes. Later models with a digital odometer may display the codes on the odometer display, followed by "done" at the end of the list. On some of these vehicles, holding the trip reset and trip/odometer buttons simultaneously, then turning the ignition on and waiting five seconds will run a little light show (okay, lamp test) and then display the codes.
Some helpful online lists of fault codes:
- 1984 through 1993 vehicles: http://minimopar.net/fault/index.html
- 1980s through present vehicles, including instrument panel self-tests and climate control system codes: http://www.allpar.com/fix/codes.html
- Specifically for the PT Cruiser: http://ptcruizer.com/computer-codes.html
I am not sure how erasing codes from the vehicle's long-term memory works. They do expire after 25 engine on/off cycles, but I am not sure how to manually clear them. Manually clearing them on demand may require a special ODB scan tool. The ECU's memory can be cleared at any time by leaving the negative battery cable disconnected for about 30 minutes, however, this may cause the car to behave strangely for the first 200 miles or so of operation until the system re-learns its proper behavior.