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Knock sensor wiring severed - how to repair?


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I had been getting a P0327 (knock sensor circuit bank 1) code on my Boxster, and today I had time to investigate. It turned out that the wiring to the knock sensor was completely severed at the connector (see picture; this is the connector on the engine harness that plugs into the knock sensor).

How do I best repair this? Can these connectors be bought somewhere?

Thanks in advance for any feedback...

post-68203-0-97936700-1332217397_thumb.j

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It will be possible to push the pins out, split open the crimp and insert a new length of wire (say 2") and recrimp them. Then solder to the wiring in the car and cover with double wall heat shrink. If what I have just said scares you, then perhaps repeat that to an automotive electrical guy or even a car stereo installer.

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It will be possible to push the pins out, split open the crimp and insert a new length of wire (say 2") and recrimp them. Then solder to the wiring in the car and cover with double wall heat shrink. If what I have just said scares you, then perhaps repeat that to an automotive electrical guy or even a car stereo installer.

Thank you! I think I'll be able to do that.

But now I actually have a bigger problem: it turns out that the two wires from the engine harness are the same color (don't know why; on the other knock sensor the wires are different colored). So now I don't know which wire goes to which terminal on the connector.

How do I figure this out without trial and error? I _think_ that one wire is signal, and the other is ground?

I know from the workshop manual that the signal wire goes to DME connector, pin 13. So I guess I could do a continuity test between DME pin 13 and each of the two wires to determine which one is the signal wire. But which terminal on the knock sensor connector does the signal wire go to?

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It would be unusual for the Germans to do this unless it didn't matter, any chance that one of the wires has a color band every 4" or so? I would go with trial and error since one is gnd and one is signal, you have 50% chance of getting it right, and wrong should throw an immediate error. You could trace out the wire, but then how would you know what pin was what on the connector?

I always assume that these sensors can fail in the grounded or open state and the electronics are prepared for each possibility, so would go with the above assumptions.

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My car had a factory replacement engine about 7 years ago. Perhaps they "repaired" this part of the old harness when they put the new engine in and used the same color wire. No idea...

But I think I've figured it out. I traced the wires on the other knock sensor back to the DME. There are separate pins for knock sensor signal and knock sensor ground on the DME, so the polarity must matter.

Incidentally, I was wrong in my previous post; the DME pins I mentioned are for 97-99 Boxsters. For my 2001 S, the pins in question are on connector C at the DME (just in case someone else comes across such an issue in the future):

pin 36: signal knock sensor 2

pin 37: ground knock sensor 2

pin 49: signal knock sensor 1

pin 50: ground knock sensor 1

Based on tracing back the wires, the signal / ground pins on the knock sensor connector are shown in the picture below.

post-68203-0-87552700-1332273551_thumb.j

Edited by fluellen
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  • 2 years later...

I'm not a big fan of reopening old threads, but this one leads exactly to where I am today.

 

We are talking about an '03 base Boxster - last week the car started suddenly running really poorly, MIL light flashing, etc etc. P0327 code thrown (along with P0300, P0301 and P0306). I found that the mice had eaten the insulation off both wires going to Knock Sensor 1 and had chewed up a fair amount of the wire as well.

 

As the whole connector came off in my hand, I disassembled the connector and was able to solder some leads onto what remained and then to solder that back to the wiring harness. I based my polarity connections on how Knock Sensor 2 was wired relative to the diagrams in the Bentley. It's all buttoned back up, however, the car runs exactly the same as it did, including the flashing MIL light. I don't have a code scanner, so it will have to wait until tomorrow to see what code(s) show up.

 

I am wondering if the polarity of the connection makes any difference or not. When I go to the DME and measure resistance, both sensors give me just a hair over 5Mohms, so I know that my wiring job is at least intact. Grasping at straws here, unfortunately.

 

Any help appreciated, that's for sure.

 

Tom Coradeschi

Edited by tcora
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Answering my own question: either polarity doesn't matter, or I got the polarity correct. The only code left now is the P0306. Going with a fresh set of plugs and a careful inspection of the wiring leading to the #6 coil (important given the mouse damage noted above).

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