Experiencing trouble connecting your scan tool to your 1998 Jeep Cherokee? A check engine light illuminating on your dashboard is often the first sign that something’s amiss, prompting many owners to reach for their OBD2 scanner. However, frustration mounts when the scanner fails to establish a connection. If you’re facing the dreaded “scanner won’t connect” message with your 98 Jeep Cherokee, you’re not alone. This issue can stem from several common culprits, and thankfully, many are straightforward to diagnose and fix.
This guide will walk you through the troubleshooting steps to pinpoint why your OBD2 scanner is refusing to communicate with your Jeep Cherokee, focusing on the key areas of power, ground, and connector integrity.
Checking Power to Your OBD2 Port (DLC)
The first step in diagnosing a connection problem is to verify that your OBD2 port, also known as the Data Link Connector (DLC), is receiving power. Without power, your scan tool simply won’t be able to initialize and communicate with your Jeep’s computer.
Here’s how to check for power:
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Locate the DLC: On a 1998 Jeep Cherokee, the DLC is typically found under the dashboard on the driver’s side. Look for a trapezoid-shaped connector, usually black or dark gray.
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Identify Power and Ground Pins: The DLC has several pins, but we’re primarily interested in the power and ground pins.
- Ground Pins: On the top row of pins, the second and third cavities from the left are ground pins.
- Power Pin: On the bottom row, the far right pin cavity is the 12VDC power supply.
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Use a Voltmeter: Set your voltmeter to measure DC voltage.
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Test for Voltage:
- Connect the black lead of your voltmeter to one of the ground pin cavities (top row, second or third from left).
- Connect the red lead of your voltmeter to the power pin cavity (bottom row, far right).
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Interpret the Reading: You should see a reading of approximately 12VDC.
- No Voltage: If you get no voltage reading, switch the black lead to the other ground pin cavity and test again. If still no voltage, proceed to check the fuse.
- Voltage Present: If you see 12VDC, then power to the DLC is likely not the issue, and you may need to investigate other potential problems like the scanner itself or communication circuits.
Inspecting the Ground Connection
A poor or missing ground connection is another common reason why a scanner won’t connect. The DLC relies on a solid ground to complete the electrical circuit.
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Locate Ground Point: The ground wires for the DLC are typically grounded at the oil dipstick tube mounting bracket stud, located on the left side of the engine compartment.
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Visual Inspection: Examine the wires connected to this ground point.
- Check for Damage: Look for any signs of damage, breaks, or fraying in the wires.
- Check for Corrosion: Inspect the terminals and the ground stud for corrosion. Corrosion can impede electrical flow.
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Test with an Ohmmeter: If the visual inspection doesn’t reveal any obvious issues, use an ohmmeter to test the continuity of the ground wires.
- Set your ohmmeter to measure resistance (Ohms).
- Connect one probe of the ohmmeter to a known good chassis ground (an unpainted metal part of the vehicle’s frame).
- Connect the other probe to each of the ground pin cavities in the DLC (top row, second and third from left).
- Continuity Reading: You should see very low resistance, ideally 0.5 Ohms or less, indicating good continuity to ground. High resistance or no continuity indicates a ground fault.
Checking Fuse F17
The power to the DLC is often supplied through a fuse. On a 1998 Jeep Cherokee, fuse F17 in the Power Distribution Center (PDC) is a likely candidate.
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Locate the PDC: The PDC is usually a black box located under the hood, often near the battery or on the fender well. Refer to your Jeep Cherokee owner’s manual for the exact location of the PDC and fuse box diagram.
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Identify Fuse F17: Consult the fuse box diagram (usually printed on the inside of the PDC cover) to locate fuse F17. It’s often labeled and its amperage rating will be indicated (e.g., 15A).
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Inspect Fuse F17:
- Visual Check: Remove fuse F17 from the PDC. Visually inspect the fuse element. If the thin wire inside the fuse is broken or melted, the fuse is blown.
- Fuse Tester (Optional): Use a fuse tester or multimeter to confirm if the fuse is blown.
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Replace if Blown: If fuse F17 is blown, replace it with a new fuse of the exact same amperage rating. Do not use a fuse with a higher amperage rating, as this can cause damage to the electrical system.
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Check Other Circuits: Fuse F17 may also power other circuits, such as the headlamps as mentioned in the original post. If your headlights are also not working, this further suggests a blown fuse F17. If replacing the fuse immediately blows it again, there’s likely a short circuit in the system that needs further investigation.
Inspecting the DLC Connector Itself
Physical damage or corrosion to the DLC connector can also prevent a scanner from connecting.
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Visual Inspection of Pins: Carefully examine the pins inside the DLC connector.
- Corrosion: Look for any signs of corrosion or rust on the pins.
- Bent or Damaged Pins: Check if any pins are bent, broken, or pushed out of position.
- Pin Expansion: Inspect if the pin cavities look widened or expanded, which can happen if probes have been forcefully inserted incorrectly, leading to poor contact.
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Clean Corrosion (If Present): If you find corrosion, you can try carefully cleaning the pins with electrical contact cleaner or a small wire brush designed for electronics. Be gentle to avoid damaging the pins.
Scanner Compatibility and Deeper Issues
While less common if your scanner works on other vehicles, consider these points:
- Scanner Compatibility: Ensure your scan tool is compatible with OBD2 and specifically with 1998 Jeep Cherokee vehicles. Some older or very basic scanners might have limited compatibility.
- SCI Circuits: If you’ve checked power, ground, fuse, and connector and still have no connection, a more complex issue might be with the vehicle’s Serial Communication Interface (SCI) circuits. These circuits are responsible for data communication between the vehicle’s computer and the DLC. Issues with the SCI circuits are more complex to diagnose and may require professional assistance.
Conclusion
Troubleshooting a “scanner won’t connect” issue on your 1998 Jeep Cherokee involves a systematic approach, starting with the basics: power and ground to the OBD2 port. By methodically checking the fuse, ground connections, and the DLC connector itself, you can often pinpoint the cause of the problem and get your scan tool communicating with your Jeep again. If these steps don’t resolve the issue, it might indicate a more complex communication problem requiring further professional diagnosis.
