The P1684 code - Definition, Causes, and Symptoms (& how to Fix it)

The P1684 code may appear on your computer if you have a Dodge or Fiat vehicle. It might cause alarm when you first see it, but in many cases, it’s easy to resolve.

We will be looking at P1684 code trouble codes in greater detail. This guide will show you how to repair the problem and what symptoms it might cause. 

Definition of Code P1684

P1684 – Battery Power To Module Disconnected

What does the P1684 code mean?

Dodge, Jeep Chrysler Dodge and Fiat determine P1684 as the indicator that the battery is disconnected after 50 start-ups. 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. If there is a malfunction or defect in the charging system (e.g. wire damage or failure of the control module), the DTC will be set. 

But, manufacturers might use P1684 codes to indicate something else. For vehicles of a specific brand, it is important to search for those codes. 

Trouble code P1684 Symptoms

You might only see the Check Engine Light if the battery is temporarily out of service. However, if there’s a voltage issue, there will be more pressing symptoms.

These are some of the most frequent symptoms associated with P1684:

• Make sure your engine light is on
• Computer memory loss 
• Problems with transmission shifting
• Trouble with multiple system sensors
• Operation error
• Problems with the power system

The P1684 Code: Causes

The problem is usually caused by the fact that the engine was running and the battery has been disconnected. Below are possible P1684 codes to look out for:

• The battery can be disconnected from the engine running, or on an ignition switch.
• You can swap out your battery without having to install a memory-keeper
• Low voltage or undercharging of the battery is a defect in the charging system
• Disconnection or corrosion between posts and terminals
• Battery ground fault
• PCM requires programing
• Defective PCM
• Wire damage

Is the P1684 Code Really Serious?

Niedrig – If you simply disconnected the car battery, it’s unlikely that there’s any issue at all. The code is set as a preventative measure and will automatically reset. However, if there’s a problem with the charging system or a control module, you should take the problem more seriously.

Neglecting to send enough voltage can lead to serious problems. Defective PCMs can cause other issues. 

Which Repairs can Fix the P1684 Cod?

If the fault doesn’t occur again within 50 start-ups, the computer will reset the code. If the problem was due to a battery being disconnected, the computer will fix it. These are just a few of the possible fixes.

• Make sure to clean the terminals of your battery chargers before you reconnect them
• Make sure you have a battery ground connection
• Replacing damaged wiring
• Programm PCM
• Replacing the PCM

Common mistakes in diagnosing P1684

Some diagnostic trouble codes are considered universal among automakers, but this isn’t one of them. The P1684 code may mean something else if you don't have a compatible car.

If your vehicle is part of the Chrysler/Dodge family, it’s important that you research your particular brand to find the cause. Mazda vehicles, for example, use this code in order to identify an oil pump sensor fault. 

How do you diagnose the P1684 trouble code?

This is how professionals mechanics approach this code.

1. An OBDII scanner can read all codes. Any other codes you find are important to repair. You should also keep in mind that voltage discrepancy may cause P1684 to occur.
2. You might have to update the PCM with any new information if your battery was recently replaced. 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. You can use a car wiring diagram to locate the issue if the code does not change or persist. 

Calculated Cost for Repair

You might need to pay for some additional expenses, aside from the waiting time that your code will reset after you change your battery.

• 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

The P1684 Code: Mechanics Tips

In some cases, the P1684 issue can cause damage to the CAN bus. This system might not work if you use a low-end code reader. A professional code scanner is better. Expert knowledge is helpful in diagnosing the fault. Further assistance may be required if the CANbus system is damaged.