P1684 Code – Battery Power to PCM/TCM Module Disconnected

Written By: Terrence Hines
Category: Error Code

The P1684 code serves as an alert that the electrical energy source supplying the PCM/TCM module has been cut off.

The P1684 code is related to an electrical issue, so it’s important to have a reliable auto technician check it out. This will help make sure that your vehicle is safe to drive.

P1684 Code – Battery Power to PCM/TCM Module Disconnected!

P1684 is a code typically associated with vehicles equipped with an onboard computer, otherwise known as a Powertrain Control Module (PCM) or Transmission Control Module (TCM).

This P1684 code indicates an issue that interferes with the vehicle’s power supply, wiring, or battery connections.

If P1684 appears on your vehicle’s diagnostic tests, it means that the power sent from your car’s battery to the PCM or TCM has been compromised somehow.

P1684 Code – Battery Power to PCM/TCM Module Disconnected!

It is possible that this issue can be attributed to corrosion, dirty connections, and wiring damage; however, it could also suggest there are bigger challenges.

To avoid any further issues in the future, make sure you have P1684 taken care of quickly!

Symptoms Of The P1684 Code

P1684 is a code indicating battery power has been disconnected or interrupted from the Powertrain Control or Transmission Control Module.

Certain symptoms may arise if the P1684 code is present, such as engine misfires, reduced engine performance, and difficulty starting the vehicle.

In some cases, headlight dimming may also accompany these issues.

If your diagnostic scan reveals the presence of P1684, it is essential to thoroughly examine all wiring and electrical components connected with supplying power to the PCM/TCM module.

If necessary, be sure to replace any malfunctioning parts that may be found.

1. Illuminated CEL (Check Engine Light):

P1684 code indicates that your car’s “Powertrain Control Module/Transmission Control Module” is not supplied with enough battery power.

A P1684 code will cause the Check Engine Light (CEL) to turn on, which may alert you to a potential problem.

The P1684 code is often caused by corroded or loose connections, busted wire harnesses and/or brake light switch/stoplight switches.

Diagnostics should be conducted to determine what caused the P1684 code for it to be properly repaired and your CEL to turn off.

2. A Lack Of Power When The Vehicle Is Running:

P1684 code is a generic, powertrain-related diagnostic trouble code (DTC) that indicates the Battery Power to a PCM/TCM Module has become disconnected.

This lack of power can manifest itself in a variety of ways when the vehicle is running, ranging from decreased engine performance to intermittent stalling or shutting off.

If the P1684 code is registered, you may want to consult with a certified mechanic to ensure that your battery and any other related components are being connected appropriately.

3. Poor Fuel Economy:

P1684 is a diagnostic trouble code that can affect the performance of your vehicle’s powertrain control module (PCM) or transmission control module (TCM).

Poor Fuel Economy

This code typically indicates that the battery has been disconnected from the PCM or TCM, resulting in poor fuel economy.

If P1684 appears on your diagnostic trouble code reader, you’ll need to diagnose and determine the cause of the battery disconnection before it can be fixed.

Issues such as loosened connections, mechanical or electrical faults, or corroded pins may contribute to P1684 and should be ruled out when seeking a resolution.

4. Stalling Or Misfiring Engines:

P1684 is a trouble code for engines that could cause your engine misfiring or stalling.

To diagnose P1684 and resolve the issue, it’s important to use an OBD-II scanner to find out what’s causing the trouble code.

Many things could cause P1684. However, before you try to fix it, you need to find out what is causing the problem.

This step is vital to determine the source and locate an effective solution to address the root cause.

5. Difficulty Starting The Car:

P1684 is a trouble code that indicates an issue with the connection between the car’s battery power and one of its electronic modules.

When a vehicle fails to start, the P-code is likely causing the problem.

This code indicates an issue with communication between components that must be connected for the car to turn on and run properly.

To repair P1684 and get your car running again, it’s important to diagnose the underlying cause so that the proper solution can be applied.

Common Problems That Can Cause The P1684 Code

P1684 is a code that means there might be something wrong with the power supply to the powertrain control module (PCM) or the transmission control module (TCM).

Typically, this is caused by an issue with the battery connections, either through loose wires or a worn-down terminal.

Without a steady power supply, these computerized systems cannot operate correctly, consequently triggering P1684 for diagnostics.

P1684 Code

Inspecting the battery connection and fixing any loose wiring is important to ensure P1684 does not pop up again.

1. Loose Connections Between The Battery And Computer Module:

P1684 is the code for issues between the computer module and a car’s battery. The most common culprit is loose connections.

If your connection does not meet the security protocols, it’ll fail to establish a link between the battery and the computer module. This results in P1684 showing up on your diagnostic test.

To fix this issue, simply remove the battery connectors and remove any corrosion or dirt using a cleaning agent such as rubbing alcohol.

Then connect them back up and make sure they are tightly sealed into place. This should only take a few minutes, and you will be on your way with a P1684-free car!

2. Damaged Wiring Harnesses Near The PCM/TCM Module:

P1684 is a code many people have encountered while using their vehicle, typically accompanied by the illuminating check engine light.

Many times, the P1684 code is caused by damage to the wires near the PCM/TCM module inside the car. These issues can cause bigger problems if they are not fixed.

While individual wire repairs are possible, it’s often best to replace the entire harness for a better guarantee of success.

If you’ve noticed P1684 on your dash, please look at these vital parts of your car as soon as possible before further damage occurs.

3. Bad Relays Or Connectors Within The Module Itself:

P1684 codes can be a major automotive nuisance, as they indicate an issue with the internal circuitry within the Powertrain Control Module.

P1684 codes can be caused by a malfunction in the power supply or other components not functioning correctly, usually due to an issue with relays or connectors within its mainframe.

P1684 codes can come back unless the problem is fixed. It is a good idea to take your car to get checked out as soon as you see this code on your instrument panel.

4. A Faulty PCM/TCM Module:

P1684 is a code that appears on many vehicles, usually related to something wrong with the Powertrain Control Module (PCM) or Transmission Control Module (TCM).

Sometimes, it can be caused by an issue with the PCM/TCM module, such as a malfunctioning sensor, blown fuse, or wire insulation issue.

It’s important to be aware of P1684 and what could cause it, as not properly diagnosing and fixing this problem could lead to plenty of more expensive issues down the line.

If you think you may be dealing P1684 related issues, try having a professional look at your vehicle for a full diagnostic test as soon as possible.

5. Corrosion On The Battery Terminals:

Corrosion on the battery terminals can be a major cause of the P1684 codes.

Corrosion On The Battery Terminals

This code will appear when your vehicle’s internal computer detects a voltage discrepancy between the two battery terminals.

This can indicate an open circuit; corrosion around the terminals is often the culprit.

Left untreated, corrosion may weaken the electrical connection to other components in your vehicle and increase resistance, eventually resulting in power loss or faulty readings.

It’s important to regularly inspect and clean your battery terminals, so they don’t corrode further and result in P1684 codes!

How To Fix The P1684 Code?

P1684 code is a trouble code that indicates the battery power to your Powertrain Control Module (PCM), or Transmission Control Module (TCM) has been disconnected.

Thankfully, the P1684 code can usually be resolved quickly and effortlessly.

Start by checking any fuses associated with the P1684 code, as these are common culprits of electrical failure.

Ensure all connections are secure and clean, then reset the codes and attempt to start the car after unlocking it from “limp home mode,” if applicable.

If all else fails, it may be worth considering a new PCM or TCM module as the ultimate solution.

If you want to switch up your vehicle’s control modules, it is recommended that you look for specialist help.

You may be in an even more complicated predicament without a comprehensive understanding of properly configuring these devices.


P1684 code is a warning that your vehicle’s power to the computer has been disconnected.

It could be due to a loose power wire connection, corroded terminals, or failed part of the charging system.

Given its potential for causing additional harm, P1684 should not be taken lightly and must be dealt with appropriately and within a reasonable timeframe.

Make sure to take your car to a mechanic that knows what they are doing.

They will help you fix any issues that could cause the P1684 code to fail. This will help avoid any potential problems in the future.

Terrence Hines

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