The code P1684 states the battery has been disconnected within the last fifty starts. However, with these vehicles it isn't necessarily a 'battery disconnect' code, but somehow the battery power to the PCM was lost. This could be due to a lot of things.
Some suggest looking at the ASD (auto shutdown) relay which supplies all the power. If it stops working you may have a voltage drop or no voltage at all. This relay is located in the fuse/relay box in the engine compartment.
Others suggest a wiring harness or connector problem. (It can also be an internal PCM connection (solder joint?) problem.
The location of the battery close to the PCM makes any unsealed connectors prone to corrosion from battery acid misting. Look carefully at the connector terminals. Unplug and re-plug connectors for inspection and to 'scrape' a new fresh contact between the terminals as you reconnect them.
Clean battery terminals are a must. Take them off and actually brush or scrape the insides of the terminals and outsides of the posts until you see shiny lead.
When the PCM loses battery back-up, all memory and settings are lost which means it also wiped out any other fault codes that are pertinent to the hard starting issue.
Good luck on your troubleshooting!
Check the connections at the computer. Dodge put it in the passenger fenderwell where it gets wet and corroded.
SOURCE: While driving my 2002 Buick rendezvous the battery
check electrical connections between battery and fuses in engine compartment, check connection at starter
SOURCE: car wont start, acts like
Check the battery +12v power connection to the starter is in good order,
Check the ground connection between the battery negative and the engine/starter motor is robust and intact.
If no problem with above, replace the starter motor.
SOURCE: my honda civic 2003 si loses electrical power in
you may have a faulty alternator or and internal part in the alternator, replace it with a dealer part and that may solve the problem, it must be a dealer part..
SOURCE: My 2005 Chrysler Town and Country. When I try to
Its possible that the Starter is bad. But check your Starter relay first. If you use jumper cables and bridge the main cable on one side of the Relay to the opposite side, and it works, the Relay is bad. About $15 for the part.
When you test for Battery voltage, hook the POS end of your charger to the Battery side of the Relay. If your Battery post is dirty, you may have 12 or more Volts at the Battery, but nothing at the Solenoid. Then you just need to clean the cable and try it.
If you get the Van to run, you can always go to Autozone or Oreillys and have them do a Starter draw test. Then you will be confident about the Starters' condition and you will not have to remove it for nothing. The tests are free as well as them using a scanner on your vehicle.
SOURCE: I have a 2003 VW
Ignition switch has a short, same thing happened to me and I went through all the relays and a starter before I found it.
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