Experiencing issues connecting your OBD2 scanner to your 2005 Nissan Murano? You’re not alone. A failure to establish communication with the OBD2 port can be a frustrating roadblock when trying to diagnose car problems. This guide will walk you through potential causes and troubleshooting steps, inspired by a real-world scenario from a fellow Nissan Murano owner.
Let’s delve into a situation where a simple repair attempt led to an OBD2 connection problem, and explore how to approach this issue methodically.
The Junkyard Coil Conundrum
The story begins with a 2005 Nissan Murano experiencing engine misfires. In an attempt to quickly resolve a cylinder #4 misfire, the owner visited a junkyard for a replacement ignition coil. Unfortunately, a well-intentioned but misguided junkyard worker installed a mismatched coil, claiming it was compatible due to connector similarities. This immediately caused the car to fail to start.
Upon realizing the error and reinstalling the original coil, the problem escalated. The ignition ECCS fuse started blowing upon cranking, and crucially, the OBD2 scanner failed to connect to the vehicle’s computer.
Symptoms and Initial Checks
After the coil incident, the key symptoms were:
- No OBD2 scanner connection: The scanner could not communicate with the car’s computer (ECU/ECM).
- IGN ECCS fuse blowing: This fuse protects the engine control system and ignition.
- No start: The engine would crank but not start.
- Radiator fans running: The radiator fans turned on immediately when the ignition was switched on, even when the engine was cold.
- No fuel or exhaust smell: Indicating a potential fuel delivery or ignition issue.
The owner diligently performed initial checks, including:
- Fuse replacement: Replacing the blown IGN ECCS fuse.
- Connector cleaning: Cleaning electrical connectors, possibly looking for corrosion or damage.
- Battery and grounding checks: Disconnecting the battery and checking grounding points for good connections.
- Harness inspection: Inspecting the wiring harness from the ignition coil connectors to the main harness for shorts or melted wires.
- OEM coil pack replacement: Installing a set of second-hand OEM ignition coils.
Despite these efforts, the OBD2 connection remained unavailable, and the car still wouldn’t start.
Potential Causes for OBD2 Connection Failure
When your 2005 Nissan Murano refuses to communicate with an OBD2 scanner, several possibilities come into play:
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Blown Fuse: While the IGN ECCS fuse was addressed, there might be other fuses related to the OBD2 port or ECU power supply that are blown. Check the OBDII fuse specifically, often located in the interior fuse box. Refer to your Murano’s owner’s manual for fuse box diagrams.
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OBD2 Port Issues: The OBD2 port itself could be damaged. Inspect the port for bent or broken pins. Less commonly, the port wiring could be compromised.
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Wiring Harness Problems: Although a visual inspection was done, there could be subtle damage to the wiring harness leading to the OBD2 port or ECU. Look for chafed, pinched, or broken wires.
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ECU/ECM Malfunction: The most concerning possibility, especially given the initial coil mishap, is damage to the Engine Control Unit (ECU) or Engine Control Module (ECM). The incorrect coil might have sent a voltage spike or incorrect signal that damaged the ECU’s communication circuitry.
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Grounding Issues: While grounding points were checked, a poor ground connection can cause a wide range of electrical problems, including OBD2 communication failure. Double-check all engine and chassis ground connections for tightness and cleanliness.
Troubleshooting Steps for No OBD2 Connection
Here’s a systematic approach to diagnose the OBD2 connection problem in your 2005 Nissan Murano:
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Fuse Check (Again): Thoroughly check all fuses related to the engine management system and OBD2 port. Don’t just visually inspect them; use a multimeter to confirm continuity.
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OBD2 Port Inspection: Visually examine the OBD2 port for damage. Try using the OBD2 scanner on another vehicle to ensure the scanner itself is working correctly.
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Power and Ground to OBD2 Port: Use a multimeter to check for power and ground at the OBD2 port. Pin 16 should have battery voltage (12V+), and pins 4 and 5 should be ground. If power or ground is missing, trace the wiring back to the fuse box and ground points.
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ECU Power and Ground: Locate the ECU (typically under the dashboard or in the engine bay – consult your service manual). Check for power and ground at the ECU connector. Pinouts for the ECU will be needed, which can be found in a repair manual or online wiring diagrams for the 2005 Nissan Murano.
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CAN Bus Check (Advanced): The OBD2 system uses a CAN (Controller Area Network) bus for communication. If you have experience with electrical testing, you can check the CAN bus signals at the OBD2 port (pins 6 and 14) using an oscilloscope or a specialized CAN bus tester. However, this is an advanced step and may require professional equipment and expertise.
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ECU Replacement (Last Resort): If all other possibilities are exhausted and you suspect ECU damage, ECU replacement might be necessary. However, ECU replacement can be complex, potentially requiring programming to match your vehicle. It’s highly recommended to consult a professional mechanic or Nissan specialist before replacing the ECU.
The Immediate Fan Issue and No Start Condition
The radiator fans running continuously when the ignition is on is another symptom pointing towards potential ECU or sensor issues. The ECU controls the radiator fans based on temperature sensor readings. If the ECU is malfunctioning or receiving incorrect sensor data, it could activate the fans unnecessarily.
The “no start” condition, combined with the lack of fuel or exhaust smell, suggests a potential fuel delivery or ignition problem. However, with the OBD2 connection down, pinpointing the exact cause becomes significantly harder.
Seeking Professional Help
Given the complexity of diagnosing electrical issues and potential ECU damage, especially without OBD2 access, seeking professional help is highly recommended. A qualified mechanic with experience in Nissan vehicles and automotive electronics will have the tools and expertise to properly diagnose the root cause of the OBD2 connection failure and the no-start condition in your 2005 Nissan Murano.
While DIY troubleshooting is valuable, sometimes professional intervention is necessary to resolve complex automotive problems efficiently and effectively.
