Experiencing a no OBD2 communication issue on a 1999 Dodge Ram 1500 can be frustrating, especially when trying to diagnose other potential problems like transmission issues. This article provides a step-by-step guide to troubleshoot why your scan tool might not be communicating with your 1999 Dodge Ram 1500’s computer system. We’ll explore common causes and diagnostic procedures to help you get your OBD2 port working again and get to the bottom of your truck’s issues.
Understanding OBD2 Communication Problems
The OBD2 (On-Board Diagnostics II) port is crucial for diagnosing modern vehicles. It allows scan tools to interface with the vehicle’s computer, retrieve diagnostic trouble codes (DTCs), and access live data. For a 1999 Dodge Ram 1500, the OBD2 system is essential for identifying issues within the engine, transmission, and other vehicle systems. When there’s no OBD2 communication, it means your scan tool cannot establish a connection with the truck’s Powertrain Control Module (PCM), hindering your ability to diagnose problems effectively.
Common Causes of No OBD2 Communication on a 99 Dodge Ram 1500
Several factors can lead to a lack of OBD2 communication in your 1999 Dodge Ram 1500. Here are some common culprits to investigate:
- Blown Fuse: The OBD2 port is typically powered by a fuse. A blown fuse is the simplest and most common reason for communication failure. Check your fuse box diagram (usually located on the fuse box cover or in your owner’s manual) and identify the fuse for the cigarette lighter or auxiliary power outlet, as the OBD2 port often shares this circuit.
- OBD2 Port Wiring Issues: Damage to the wiring harness leading to the OBD2 port can disrupt communication. This includes:
- Power Wire (Pin 16): This pin should have 12V power. Issues here mean the port isn’t getting power.
- Ground Wires (Pin 4 & 5): Proper grounding is essential for circuit completion.
- Communication Wires (Pins 6 & 14 – CAN High & CAN Low, or Pin 7 & 15 – ISO 9141-2 K & L lines, depending on the specific system): Damage to these wires can interrupt data transmission between the PCM and the scan tool.
- Faulty OBD2 Port Connector: The OBD2 port itself can be damaged or corroded, preventing proper contact with the scan tool.
- PCM Problems: While less common, a faulty PCM can also be the reason for no OBD2 communication. If the PCM is not functioning correctly, it may not respond to requests from the scan tool.
- Wiring Harness Issues Between PCM and OBD2 Port: Damage or breaks in the wiring between the PCM and the OBD2 port can disrupt the communication pathway.
Diagnostic Steps for 99 Dodge Ram 1500 OBD2 Communication Failure
Follow these steps to diagnose the no OBD2 communication issue on your 1999 Dodge Ram 1500:
- Check the Fuses: Locate the fuse box and identify the fuse for the cigarette lighter/auxiliary power outlet. Inspect the fuse for any signs of being blown (broken filament). Replace it with a fuse of the same amperage rating and re-test OBD2 communication.
- Inspect the OBD2 Port: Visually examine the OBD2 port for any signs of damage, corrosion, or bent pins. Clean the port with electrical contact cleaner if necessary.
- Verify Power and Ground at the OBD2 Port: Use a multimeter to check for power and ground at the OBD2 port:
- Pin 16 (Power): Should read 12V with the ignition ON. Test between Pin 16 and a known good ground (like the vehicle chassis).
- Pin 4 & 5 (Ground): Test for continuity to ground (0 ohms resistance) between these pins and a known good ground.
- Check Wiring Continuity: If power and ground are present, check the continuity of the communication wires between the OBD2 port and the PCM. Refer to a wiring diagram for your 1999 Dodge Ram 1500 to identify the correct pins on both the OBD2 port and the PCM connector for the communication lines (likely pins connected to the vehicle’s diagnostic bus). Use a multimeter to test for continuity (low resistance) on these wires. Also check for shorts to ground and shorts to power on these communication wires.
- PCM Inspection (Advanced): If wiring checks out, the PCM itself might be the issue. This is a more complex diagnosis and may require professional equipment. You could check for power and ground at the PCM connector itself, and if possible, perform a PCM reset (disconnect battery for a period, consult repair manual for specific procedure).
Could Transmission Issues Be Related to OBD2 Communication?
While seemingly unrelated, transmission issues can sometimes be indirectly linked to OBD2 communication problems. The PCM controls both engine and transmission functions. If the PCM is faulty or has communication issues, it could affect both OBD2 diagnostics and transmission operation.
In your specific case, mentioning transmission problems and no downshifting after a transmission swap, alongside the no OBD2 communication issue, could suggest a PCM or wiring harness problem affecting both systems. It’s crucial to resolve the OBD2 communication issue first to retrieve any potential DTCs related to the transmission or PCM, which could provide valuable clues.
Conclusion
Troubleshooting a 99 Dodge Ram 1500 with no OBD2 communication requires a systematic approach. Start with the simple checks like fuses and port inspection, then move on to verifying power, ground, and wiring continuity. While a faulty PCM is a possibility, thorough diagnosis of the simpler components is essential first. Resolving the OBD2 communication is the first step towards effectively diagnosing and addressing any underlying issues, including potential transmission problems you might be experiencing. If you are uncomfortable with these diagnostic steps, seeking assistance from a qualified mechanic is recommended.
