I need help diagnosing a toyota knock sensor issue.

[joegreen]

I meant to put this in the automotive electrical forum but accidentally posted it here as i was looking at other posts in this section. My bad.
So i have a 2000 lexus es300 with the p0330 knock sensor code. This vehicle has the 1mzfe engine and the knock sensors are very hard to get to and they are expensive $180 a piece. Usually when this code shows up it is either the knock sensor or the wiring harness going to the knock sensor that is bad. It can also be the ecm but i dont believe it is in this case. The toyota knock sensors are a little different than most other knock sensors and its best to use an oscilloscope to diagnose the sensors. Anyway i have a very rudimentary oscilloscope i made via an old headphone cable that plugs into my phone. I followed the factory service manuals oscilloscope section. It said to test the oscilloscope with the engine at 4000 rpm. This car has two knock sensors one for bank one and one for bank two. I cant get to either knock sensors but i can get to the end of the wiring harness that is connected to both sensors. I hooked my oscilloscope up to the end of the harness and tested the waveform at 4000 rpm. It looked good for the one knock sensor. I hooked the oscilloscope up to the other knock sensor and it looked ok at lower rpm idle to around 2000 but when i brought it up to 4000 rpm and held it there the waveform looked ok but it would periodically drop out to a 0v flat line and then come back to normal and then drop out again. I switched back to the other sensor it it was fine. I switched back to this sensor and it was doing the same thing again periodically dropping voltage. Seeing as i cannot get to the knock sensor i can only get to the end of the harness that could also be the problem does this sound like a knock sensor issue or a wire harness issue. The wiring harness lives under the intake manifold and it can get brittle with age so i have heard. I thought a knock sensor either works or it does not? I have not heard of them working intermittent. If it is the wiring harness that would would make sense. I tried tugging on the harness and moving it all round but i could not get it to loose signal unless i ran the engine up to 4000 rpm. Here is a video explaining toyota knock sensors. https://www.youtube.com/watch?v=L8xRJIWkHuo

 

[anndel]

Look for any physical damage to the wiring harness or connector. I've seen incidents where rodents that chewed up wires. if looks ok can you get to both knock sensors? I know you said you can't but if you can swapping the sensors with each other, e.g., Bank 1 sensor to Bank to and vice versa. Then scope it again to see if the 0v drop out moves to bank 1. That way you confirmed it's the sensor and if not trace and check the wiring harness which is a pain and the last thing I do. Good luck!

 

[StevieC]

I would swap the sensors around if possible. I know you said it's hard to get to but this would definitely determine if it's the wiring or the sensor if the problem moves or doesn't sort of thing. In most cars it's usually the sensor when this code sets but in your case because the wiring is a known problem in this model of vehicle you want to be sure. Or buy a sensor with a return policy if it's absolutely not possible to swap the sensors around.

Good luck.

 

[joegreen]

they 100% cannot be accessed without taking off the intake plenum and then the intake manifold. here is a picture of the location of the sensors in red.

 

[joegreen]

i dont want to say its the wiring harness but i have had two mice die in the blower motor and i can see some batting down where the knock sensors and harness would be.

 

[anndel]

Ouch, sorry did not know it was the inaccessible. You may be right though, it could be the harness. I read mice and rats chew through electrical wiring all the time and even shorted out the a/c evaporator in our office.

 

[mehullica]

Seen dozens with bad shielding in the sub-harness for the knock sensors. Dozens of bad knock sensors as well. Replace 2 sensors & the sub harness. While you're there replace the thermostat with an OEM one

 

[clinebarger]

I have always swapped the 2 pins at the connector.......If it now sets DTC P0325, Bank 2 knock sensor or the jumper harness has a problem. This at least eliminates the PCM & Engine harness as possible causes.

The shop I've been working at the last 6 months uses these HERE
*They have Denso embossed right on the sensor & appear identical to the OEM sensors, I've personally installed 3 sets & have not had a comeback yet. *The service manager said they have installed several more sets in the past without issue.
*A whole pallet of these sensors "could" have got damaged & Toyota/Denso or the Carrier will write the whole pallet off! I'm NOT saying that's what happened......But it happens quite often (My wife works for DHL)
*They come without the original packaging.

 

[joegreen]

I thought about testing the sensor when the intake manifold was removed but then it occurred to me I can't start the car because the intake is removed. I'll think on it some more and shop around. Thanks for the link clinebarger. Those sensors did get good reviews. I am just skeptical though. I have seen many knockoff knock sensors on eBay and such.

 

[nthach]

A lot of the Lexus guys on the LS and GS models with V8s replace the wiring harness from the sensors to the main wiring loom for the engine. Toyota used coaxial cable, like RG-6 cable/satellite TV cable to help reduce interference. The connectors get brittle as well even though it's in the V-bank.

The knock sensor harness might be NLA from Toyota, check with your dealer.

 

[The Critic]

When I see those codes, I always recommend replacing both knock sensors along with the sub-harness. When you have both manifolds removed, I also recommend re-sealing the water inlet plate - they tend to leak. Plan to spend about 5-6 hours on the job.