Subaru G3X Diesel Warning Light Points to Knock Sensor

My Subaru Outback (2009, Diesel) showed similar symptoms last season. The auto repair process revealed the issue went beyond a knock sensor malfunction. The main problem was traced to corroded wiring connections at the engine control module, causing irregular signals and poor performance. The repair involved: Complete diagnostic scan, Testing all sensor connections, Replacing damaged wiring harness, Cleaning connector pins, Reprogramming the ECU This was a serious issue requiring specialized equipment. The car problems included unusual stalling, increased fuel consumption, and inconsistent idle, matching your symptoms. Without proper repair, it could lead to further engine damage and decreased fuel efficiency. After fixing the wiring connections and updating the system, all malfunction indicator warnings cleared and the engine returned to normal operation. The rough idle completely disappeared. Worth checking the wiring harness and connections before replacing sensors. These electrical issues are common in this generation of Subarus, especially around the 35000-40000 km mark.

Thanks for sharing those details about the wiring harness repair. My G3X had nearly identical car problems and the check engine light behavior you described. After seeing your post, I went ahead with a full diagnostic and wiring inspection. Really helped sort out the ignition timing issues I was experiencing. Just curious, what did the complete repair end up costing you? Also, have you noticed any other issues popping up since getting it fixed? My fuel efficiency has definitely improved but still keeping an eye on things.

Glad my experience helped guide you. After taking my Subaru to the mechanic, they confirmed the knock sensor was indeed defective, but it turned out to be just a faulty connection rather than the sensor itself. The repair only cost 95€ to fix the cable and clean the connector area, much less than replacing the entire knock sensor unit. Since fixing the knock sensor connection, fuel efficiency has returned to normal and the engine runs smoothly without any check engine warnings. The rough idle completely disappeared and the auto repair shop confirmed all sensor readings are now within spec. It has been running perfectly for several months with no additional issues appearing. The key was catching it early before the faulty sensor signals could cause any engine knock or long-term damage. Regular checks of sensor connections can prevent these issues from developing into more serious problems. When these components start failing, they tend to trigger multiple symptoms that can be confusing to diagnose.

Following through on your advice turned out to be the right call. Got my G3X checked at a local specialist workshop last week. The malfunction indicator problem was indeed tied to faulty wiring, not just the knock sensor as initially suspected. The full diagnostic and repair came to 180€, which included cleaning all connections and replacing a section of damaged wiring. The poor performance issues cleared up immediately after the fix. No more warning lights or rough idle problems since then. Really relieved I addressed this before any serious engine damage occurred. The improved fuel economy alone makes it worth the repair cost. After a week of normal driving, the engine runs smoother than it has in months. The ignition timing is spot on now and performance feels like new again. For anyone facing similar symptoms, definitely worth getting those wiring connections checked before jumping to sensor replacements. The repair was quicker and cheaper than expected.