Decoding OBD2 Code P1684: Understanding PCM Power Interruption

The OBD2 code P1684 can be a puzzling one for vehicle owners and even seasoned mechanics because it doesn’t always trigger the check engine light. This code, generally defined as “PCM Power Input Signal Interrupted/Lost,” indicates an issue with the power supply to your car’s Powertrain Control Module (PCM). While it might not seem immediately critical, understanding and addressing this code is crucial for maintaining your vehicle’s long-term health and reliability.

The PCM is essentially the brain of your engine management system. It’s a sophisticated solid-state electronic device, highly sensitive to voltage fluctuations. Just like any computer, if the voltage supplied to the PCM drops too low, even momentarily, it can lead to operational glitches and trigger diagnostic trouble codes like P1684. Think of it like this: if your home computer suddenly loses power and then comes back on, it might restart unexpectedly or experience errors. The PCM can react similarly to power interruptions.

One common, and often overlooked, culprit behind the P1684 code is a weak or aging car battery. As batteries age, their ability to maintain a consistent voltage, especially under the heavy load of engine starting, diminishes. During engine cranking, the voltage demand is at its peak. In vehicles with older batteries, this voltage can dip significantly. If this voltage drop falls below the PCM’s operational threshold, even for a split second, the PCM can lose power momentarily. When the voltage stabilizes after the engine starts, the PCM detects this power interruption and logs the P1684 code.

![Car Battery Terminal Connection](https://blogger.googleusercontent.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Decoding OBD2 Code 1684: PCM Power Interruption – Causes and Solutions

The On-Board Diagnostics II (OBD2) system in modern vehicles is designed to monitor various aspects of your car’s operation, including its electrical systems. When something goes wrong, it often triggers a diagnostic trouble code (DTC) to help pinpoint the issue. Among these codes, 1684 Code Obd2, or simply P1684, is a somewhat unique case. It indicates a “PCM Power Input Signal Interrupted/Lost” problem, but unlike many other OBD2 codes, it typically doesn’t illuminate the check engine light (CEL).

Understanding the PCM and Power Supply

The Powertrain Control Module (PCM) is the central computer of your vehicle’s engine and transmission management system. It relies on a stable and consistent power supply to function correctly. The PCM, being a solid-state electronic device packed with semiconductors, is sensitive to voltage fluctuations. Semiconductors, the building blocks of modern electronics, require a certain voltage and current threshold to operate. If the voltage drops too low, even momentarily, these components can malfunction or cease to function altogether, leading to logic errors and potentially triggering codes like P1684.

The Weak Battery Theory Behind Code 1684

One compelling theory, supported by anecdotal evidence from mechanics and car owners, points to a weak or aging battery as a primary cause of the 1684 code obd2. Here’s how it works:

As a car battery ages, its internal resistance increases, and its capacity to hold a charge diminishes. While an older battery might still have enough power to start your car under normal conditions, it can struggle when faced with extreme temperature changes or when it’s slightly discharged.

During the engine starting process, the starter motor draws a significant amount of current from the battery. This high current draw can cause a temporary but substantial drop in the battery’s voltage. In a vehicle with a healthy battery, this voltage drop is minimal and doesn’t affect the PCM’s operation. However, with a weaker or worn battery, the voltage drop during cranking can become more pronounced, potentially falling below the minimum voltage required for the PCM to operate without interruption.

This momentary power interruption to the PCM, even if it lasts for just milliseconds, can be enough to trigger the 1684 code obd2. Once the engine starts and the charging system kicks in, the voltage quickly returns to normal, and the PCM resumes its functions. However, the system logs the power interruption event as code P1684. This explains why the code might appear even when there are no other apparent electrical issues, and why replacing an aging battery often resolves the problem.

Other Potential Causes of Code 1684

While a weak battery is a frequent cause, other electrical issues can also lead to PCM power interruptions and the 1684 code obd2. These include:

• Loose or Corroded Battery Terminals: Poor connections at the battery terminals can restrict current flow and cause voltage drops, especially under heavy load. Corrosion can build up over time, hindering proper electrical contact. Cleaning and tightening battery terminals is a simple but often effective troubleshooting step.
• Faulty Wiring or Connectors: Damaged, frayed, or corroded wiring in the PCM’s power supply circuit can also cause intermittent power interruptions. This could be due to environmental factors, road salt, or general wear and tear. Inspecting the wiring harness and connectors for any signs of damage is essential.
• PCM Malfunction (Less Common): In rare cases, the PCM itself might be faulty and misinterpret normal voltage fluctuations as power interruptions. However, this is less likely than battery or wiring issues and should be considered after ruling out other possibilities.

Symptoms and Diagnosis of Code 1684

One of the peculiar aspects of the 1684 code obd2 is that it rarely triggers the check engine light. It’s often stored as a “soft code” or “history code,” meaning it’s recorded in the PCM’s memory but doesn’t necessarily indicate an ongoing problem at the moment of diagnosis. You might only discover it when scanning your vehicle’s computer for codes using an OBD2 scanner.

While there might not be any obvious symptoms directly linked to code P1684, some drivers have reported experiencing:

• No noticeable symptoms: This is the most common scenario, as the code often doesn’t affect vehicle operation in a perceptible way.
• Slight hesitation during startup: In some cases, the momentary PCM power interruption might cause a very brief hesitation or slightly extended cranking time during engine start.
• Intermittent and unrelated electrical glitches: Although less directly related, in severe cases of power supply issues, you might observe other electrical anomalies, such as flickering lights or minor electronic malfunctions, especially if the root cause is more than just a weak battery.

To diagnose code P1684, follow these steps:

1. Check for other codes: Use an OBD2 scanner to check for any other DTCs present in the system. Sometimes, code P1684 can appear alongside other codes that might provide more clues about the underlying issue.
2. Battery Load Test: Perform a load test on your car battery to assess its health and capacity. This test will reveal if the battery is weak or failing to hold a charge adequately.
3. Inspect Battery Terminals and Connections: Visually inspect the battery terminals for any signs of corrosion or looseness. Clean the terminals and ensure they are securely tightened.
4. Wiring Inspection: Carefully examine the wiring and connectors related to the PCM’s power supply. Look for any damage, fraying, or corrosion.
5. Professional Diagnosis: If the above steps don’t resolve the issue, or if you are uncomfortable performing these checks yourself, it’s advisable to consult a qualified mechanic for a professional diagnosis.

Solutions for Code 1684

The solution to 1684 code obd2 depends on the underlying cause:

• Replace the Battery: If a battery load test indicates a weak or failing battery, replacing it with a new, high-quality battery is often the most effective solution. This is especially true if the battery is several years old or if you’ve experienced other signs of battery weakness, such as slow cranking in cold weather.
• Clean and Secure Battery Terminals: If corrosion or loose terminals are the issue, thoroughly cleaning the terminals with a wire brush and baking soda solution, and then securely tightening them can resolve the problem.
• Repair Wiring or Connectors: If faulty wiring or connectors are identified, these need to be repaired or replaced by a qualified technician.
• PCM Replacement (Rare): If all other potential causes have been ruled out, and the code persists, PCM replacement might be considered as a last resort. However, ensure proper diagnosis by a professional before replacing the PCM, as it’s an expensive component.

Conclusion

The 1684 code obd2 serves as a valuable indicator of potential electrical system issues, particularly related to PCM power supply. While often benign and linked to a simple cause like a weak battery, it’s essential not to ignore this code. By understanding the potential causes and following a systematic diagnostic approach, you can effectively address the root problem and ensure the reliable operation of your vehicle’s engine management system. In many cases, a simple battery replacement or cleaning of battery terminals can resolve the issue, preventing more significant electrical problems down the road. If you’re uncertain about diagnosing or repairing the problem yourself, seeking professional help from a qualified mechanic is always a prudent step.