Here's a breakdown of how to troubleshoot and repair a P0628 code:
1. Visual Inspection:
* Alternator: Start by visually inspecting the alternator itself. Look for any obvious damage, loose wiring, corrosion, or broken components.
* Wiring and Connectors: Carefully examine the wiring harness leading to and from the alternator. Check for any frayed wires, broken insulation, corrosion on the connectors, or loose connections. Pay close attention to the connector at the alternator and the PCM connector.
* Battery Terminals: Make sure your battery terminals are clean, tight, and corrosion-free. A bad connection here can cause all sorts of electrical gremlins.
2. Voltage Testing:
* Battery Voltage: With the engine OFF, check the battery voltage. It should be around 12.6V. A low voltage battery can trigger this code.
* Alternator Voltage (Engine Running): With the engine running, check the voltage at the battery terminals. It should be between 13.5V and 14.5V. If it's lower, the alternator isn't charging properly.
* Alternator Field Voltage (Engine Running): This is more complex and may require a multimeter with a low amperage setting, often referred to as a "milliammeter". You'll need to find the wire that goes to the alternator's field terminal (usually a smaller gauge wire). Measure the voltage at that wire while the engine is running. You may need a wiring diagram to identify the specific wire. A low or no voltage here directly points to the field circuit problem.
3. Testing the Alternator:
* If voltage tests suggest alternator failure: The best way to test an alternator is with a load tester. This tool simulates the electrical load on the alternator and will accurately determine if it's functioning correctly. Auto parts stores usually offer this service for free.
* Avoid bench testing: While some recommend bench testing the alternator, this is less reliable than load testing because it doesn't replicate the vehicle's electrical system demands.
4. Repairing the Problem:
* Tighten Connections: If you find loose connections or corrosion, clean them thoroughly and tighten them securely. Use dielectric grease on the connectors to prevent future corrosion.
* Replace Wiring: If you find damaged wiring, replace the affected sections.
* Replace the Alternator: If the alternator tests bad, replace it with a new one. Make sure you get the correct alternator for your specific Dodge 2500 model.
* Check the PCM (Advanced): If all the above checks out okay, there might be an internal issue with the PCM, but this is less likely and requires more advanced diagnostic tools.
Important Notes:
* Safety First: Always disconnect the negative battery terminal before working on any electrical components.
* Wiring Diagrams: A wiring diagram specific to your 2004 Dodge 2500 is extremely helpful. You can usually find these online (e.g., repair manuals websites) or at a parts store.
* Professional Help: If you're not comfortable performing these tests or repairs yourself, take your vehicle to a qualified mechanic. Misdiagnosis can lead to further damage.
Following these steps systematically should help you identify and fix the source of the P0628 code. Remember to clear the code after making repairs using an OBD-II scanner to see if the problem is resolved.
