1. Verify the Reading and Sensor Location:
* Double-check the resistance reading: Repeat the ohm test several times to ensure accuracy. Use a reliable multimeter and make sure the sensor is properly disconnected from the harness. A bad connection can throw off readings.
* Confirm sensor location: Ensure you're testing the *correct* knock sensor. 1998 Outbacks might have multiple. Consult a repair manual (online or physical) specific to your vehicle's engine to find its precise location and wiring diagram.
* Check the wiring harness: Carefully inspect the knock sensor's wiring harness for any damage, corrosion, or loose connections. Even a slight break can affect the resistance reading.
2. Consider Other Possibilities:
A faulty knock sensor is a *possible* cause of a check engine light, but other issues can trigger it:
* Bad connection: A loose or corroded connection in the knock sensor circuit can cause erratic readings and trigger the light. This is often easier and cheaper to fix than replacing the sensor.
* Other sensors: Problems with the mass airflow sensor (MAF), oxygen sensor(s), or crankshaft position sensor (CKP) can also trigger a check engine light and lead to symptoms mimicking a knock sensor issue.
* Engine problems: Actual engine damage (like worn bearings) can cause knock, but the sensor is detecting the condition, not causing it.
3. Further Diagnostics:
* Obtain the diagnostic trouble code (DTC): AutoZone may have given you a DTC number (e.g., P0325, P0330). This code provides more specific information about the problem. Knowing the DTC is vital for accurate diagnosis.
* Use a scan tool: A more advanced OBD-II scan tool can provide more detailed data than a simple check engine light reading. It can help confirm the knock sensor issue or identify other potential problems. Some auto parts stores offer free code reading.
* Consult a repair manual: A repair manual for your specific 1998 Subaru Outback will provide specifications for the knock sensor's resistance range, wiring diagrams, and troubleshooting steps.
4. Next Steps:
* If the resistance is consistently outside the specified range and the wiring is good: Replacing the knock sensor is likely the next step. Ensure you purchase a genuine Subaru part or a high-quality aftermarket equivalent.
* If the resistance is within the acceptable range or if other issues are suspected: Address those issues first. Ignoring them could lead to more significant and costly repairs.
In short: Don't jump to replacing the knock sensor just yet. Thorough testing and diagnosis are crucial to pinpoint the actual cause of the check engine light. A proper diagnosis saves money and prevents unnecessary repairs.
