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My Forester has a P0327 code. I checked the voltage on the shielded wire coming from the wiring harness to the sensor and it is 0.01 volts, not 2.5 or 5 volts. We have a recurring problem with pack rats getting into the engine compartment. I kill them within a day of discovery, but they do a lot of damage just overnight. The wire coming out from the ECU/ wire harness to the knock sensor pigtail has several rat bites in it, so I assume the 0.01 volt reading is due to another cut in the wire somewhere upstream of where I found the cuts. The harness is very tight and seems largely inaccessible from the knock sensor back toward the firewall, so was thinking of adding a new wire back to the knock sensor from closer to the ECU. Any thoughts or suggestions about adding a new shielded wire?

The car has 176,000 miles and runs great, I've owned the car since it was new. The Subaru dealer suggested not worrying about it, but if I can get the sensor working again and get rid of the check engine light without completely disassembling the engine to get to the whole wiring harness, I'd like to fix it.

Thanks.

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stupid dealer - you want that fixed, or, while not recommended, at least a resister 'hack'.

 

I'd get it fixed. The shielding is to prevent noise creating false signals that may imitate knock events.

 

get some 'clumps' from a cat litter box to place under/near the car. Also, if you know someone that keeps a snake, or maybe call a local zoo, put a snake 'skin shed' under the car. Refresh as necessary. Get a rubber snake to put under the car. Fox or other predator urine might work too. Cycle thru them so those 'prairie flounders' don't get acclimatized to any one method.

Edited by 1 Lucky Texan
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The knock sensor wire is shielded. If the mouse chewed through both layers of the wire, the signal wire is shorted to ground and will show 0v at any point.

 

If you can find and repair all of the damaged areas of the wire, it should be fine.

Worst case you'll have to buy some shielded wire and replace the whole length from ECU to the sensor.

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  • 2 years later...

I looked up how to splice Boeing 787 shielded avionic wire and followed that basic approach of creating shielded wire repair splices. I ended up getting some 16 gauge shielded wire and doing several repair splices with the aid of solder sleeves where the pack rats bit through the wire. Seems to be working as the Check Engine light is no longer on. 

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