We change the computer in our 2002 and there are 2 codes showing on the screen. P1684 & P1685

SOURCE: we change the computer in

What most likely is wrong is that the computer you have installed still has the VIN number stored in it from another vehicle, thus when you go to start it it doesn't see the information it is looking for and the "SKIM" or Sentry Key Immobilizer Module won't let the vehicle run. The fix is to have the computer reprogrammed by a dealer or by another shop that has this capability. Be aware that there is the possibility that the computer you have installed [if it is a used one from a similar vehicle] may still not work in your vehicle as some just aren't compatable with each other due to other programming and design issues. If it was a remanufactured computer you installed then most of them come without being programmed and also have to be reprogrammed before they will work. Good luck, hope this helps out a bit.

SOURCE: what to do with code

If the vehicle runs fine other than the P1684 code then it is probably the result of the battery being disconnected sometime in the recent past.
Hope this helps.

SOURCE: what are troubleshooting codes P1684 and P0456?

If both codes came at the same time and you didn't take the battery cable off, you need a purge solenoid, $40 near master cylinder. Put 3/4 tank of gas and the light will go out buy the time you get to 1/4 tank.

SOURCE: I have fault codes P1684 & P0340 on my 2002

P1684 The battery has been disconnected within the last 50 starts.

P0340


This indicates that a problem was detected in the camshaft position sensor circuit. Since it says circuit, that means the problem could lie in any part of the circuit - the sensor itself, the wiring, or the PCM. Don't just replace the CPS (camshaft position sensor) and think that will definitely fix it.
Symptoms Symptoms can include:

• Hard starting or no start
• Rough running / misfiring
• Loss of engine power

• a wire or connector in the circuit could be grounded/shorted/broken
• the camshaft position sensor may have failed
• the PCM may have failed
• there exists an open circuit
• the crankshaft position sensor may have failed

• Visually inspect all the wiring and connectors in the circuit
• Check for continuity in the circuit wiring
• Check the operation (voltage) of the camshaft position sensor
• Replace the camshaft position sensor as required
• Check the crankshaft position circuit as well
• Replace circuit wiring and/or connectors as required
• Diagnose/replace the PCM as required

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