Error Code P1684 is defined as Battery Power To Module Disconnected.

This error code is a manufacturer-specific trouble code, meaning it does not apply to all vehicles makes. Rather, it applies only to specific vehicle makes, such as Acura, Honda, Dodge, Chrysler, Jeep, and Subaru. Specification of the definition, troubleshooting, and repairs still vary from one make and model to another.

Definition

Error Code P1684 is detected when the TCM (Transmission Control Module) is disconnected from the battery power B+ or ground. It is set during the DRB III Quick Battery Disconnected procedure.

This code is common among Chrysler vehicles. The code simply means the battery is disconnected within the last 50 cycles, but when the motor is started, the voltage on the battery considerably drops. The PCM (powertrain control module, also known as ECM or engine control module in other makes of vehicles) sees it as an interruption of power, which then sets the code.

It is important to note, however, that this code doesn’t always mean the battery is disconnected, but the battery power to the PCM is low. This can also happen due to problems in the wiring harness or connector, or the power in the battery is low.

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In rare cases, the problem is in the internal PCM connection.

Common Symptoms

As with other codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. It may or may not cause drivability issues.

Possible Causes

There are multiple causes for this code to appear, such as:

  • Disconnected battery
  • Replaced or disconnected TCM
  • Defective TCM
  • Open or shorted TCM harness
  • Poor electrical connection in the TCM circuit

How to Check

Though seemingly simple, Error Code P1684 is tricky to diagnose, as the problem isn’t only caused by disconnected battery, as the definition says. Thus, when diagnosing, technicians check whether the battery is connected, then check the wirings for signs of damage in the wires that may cause lack of power. Also, the technician will check whether the battery has enough power.

How to Fix

Common repairs include:

  • Properly connecting the battery
  • Replacement of the TCM
  • Repair or replacement of the TCM harness
  • Repair or replacement of faulty connection in the TCM circuit
  • Cleaning the battery terminals

As said earlier, this code doesn’t always mean disconnected battery. It may be caused by a loose connection, a problem in the wiring, or lack of power from the battery. The battery terminals must be checked thoroughly and cleaned by brushing or scraping the insides and outsides of the terminal posts until the head can be seen shiny.

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