p1684 code – meaning, causes, symptoms (& how to fix)

p1684 - battery power to module disconnected

p1684 trouble code

if you drive a dodge, fiat, chrysler or jeep vehicle, you might get the p1684 code when scanning the computer, but what does it mean? it might cause alarm when you first see it, but in many cases, it’s easy to resolve.

in this guide, we take a closer look at the reasons for the p1684 trouble code. we also show you what symptoms the vehicle might experience and explain how to fix it. 

code p1684 definition

p1684 – battery power to module disconnected

what does the p1684 code mean?

p1684 is determined by dodge, jeep, chrysler and fiat to indicate that the battery has been disconnected within the last 50 starts. it occurs when the pcm (powertrain control module) determines that the battery is disconnected or there’s faulty voltage during one of the last 50 start-ups.

what’s interesting about this code is that it doesn’t automatically mean that the battery power has been disconnected, although that’s possible. the dtc is also set when there are malfunctions or defects in the charging system, including damage to the wires or a failing control module. 

however, other manufacturers will use the p1684 code to mean something else. if you drive a different type of vehicle, you will want to research those brand-specific codes. 

p1684 trouble code symptoms

if the battery was temporarily disconnected for a purpose, the only symptom you might see is the check engine light. however, if there’s a voltage issue, there will be more pressing symptoms.

here are a few of the most common p1684 symptoms:

  • check engine light
  • loss of computer memory 
  • issues with the transmission shifting
  • trouble with various system sensors
  • erratic operation
  • power system issues

causes of the p1684 code

in most cases, the problem occurs because the battery was disconnected with the engine running. here are some possible p1684 code causes to consider:

  • battery disconnected with the engine running or ignition on
  • swapping out the battery without installing a memory keeper
  • charging system defect that is undercharging the battery or providing low voltage
  • corrosion or disconnection between terminals and posts
  • battery ground fault
  • pcm requires programing
  • defective pcm
  • wire damage

how serious is the p1684 code?

low – if you simply disconnected the car battery, it’s unlikely that there’s any issue at all. this code sets as a precaution and it will reset itself. however, if there’s a problem with the charging system or a control module, you should take the problem more seriously.

without the proper amount of voltage being sent out, serious issues can occur. plus, if the pcm is defective, a lot of other driving issues are going to occur. 

what repairs can fix the p1684 code?

if the fault doesn’t occur again within 50 start-ups, the computer will reset the code. therefore, if the issue was caused because the battery was disconnected, it will repair itself. aside from this, here are a few more fixes that might be required.

  • clean battery terminals and reconnect
  • fix battery ground connection
  • replace damaged wiring
  • program pcm
  • replace pcm

common p1684 diagnosis mistakes

some diagnostic trouble codes are considered universal among automakers, but this isn’t one of them. unless you are working with a compatible vehicle, the p1684 code could mean something entirely different.

if your vehicle is part of the chrysler/dodge family, it’s important that you research your particular brand to find the cause. for example, mazda vehicles use this code to indicate an oil pump position sensor fault. 

how to diagnose the p1684 trouble code

professional mechanics tackle this code by following these steps:

  1. read all trouble codes with an obdii scanner. repair any other codes that might occur first. keep in mind that p1684 can cause other problems, so these issues could be caused by the voltage discrepancy.
  2. if the battery was replaced recently, the pcm might need to be updated with the new information. you might need to upload the battery’s cca rating, as well as the serial number and other data that the pcm requires to permit the proper alternator charging rate.
  3. if you don’t notice a problem, you will wait for 50 start-up cycles to see if the code goes away. 
  4. if the code persists or returns, you want to use a wiring diagram for your car to hunt down the problem. 

estimated cost of repair

aside from waiting for the code to reset itself after a battery change, here are some expenses you might deal with.

  • clean battery terminals and reconnect – $5-10
  • fix battery ground connection – $0 (unless a new wire is needed)
  • replace damaged wiring – $25-$500
  • program pcm – $75-$150
  • replace pcm – $400-$1,400

mechanics tips about the p1684 code

there are some instances when the p1684 issues will damage the can bus (controller area network). if you are using a cheap code reader, you might not be able to read this system. instead, you want to use a professional code scanner. plus, it helps to have expert knowledge to figure out this fault. if the can bus system has been damaged, you might need further help for diagnosis and repair.