1MZ-FE engine knock sensor codes will not go away

Can you clarify what you are getting when you are testing for a short to ground on the shielded wire? You should not have continuity to ground. Basically the body of the sensor grounds the circuit through the engine block.

Here is the test that we need to run on the sensor itself. Let's double check this and then we need to zero in on the wiring if you have continuity to ground on the shielded wire.

Hi, thanks for your reply. I have hard copy electrical manual FSM (can't show image of). The shield is for right front right? The two black wires at the 4 pin plug go to the shielding wrapped around the sensor wires on the sensor side and go to ground on the opposite side. I will recheck there is continuity to ground at the 4 pin plug two black wires.
There is no short to ground in the sensor, tested through wires. I have been fighting with this since February. I can't remember if the black wires tested as ground.

I will post when I have checked the ground again. Thanks

So yes the shield wires show continuity to ground when ignition is off. But now there's something peculiar with ignition on it doesn't show continuity. From the negative battery post to the a shock nut(body ground) it shows 20 ohms with the ignition on. I will investigate this. Thanks

Hi, so I fixed the corroded negative cable to body ground. Same codes P0325 and P0330 right away.There is now continuity to shock tower and negative battery post. Black shield wires read 30 ohms with ignition on continuity to ground with ignition off. Should I check the grounding of the black wires? There are two or three grounds bolted to the passenger side of the engine. Thanks

I am going to connect the shield wires to ground at the 4 pin plug. Can you see anything wrong with doing this? I can't find the ground at LH Intake manifold like the manual says.

Here's a pic of the shields going to ground.

Hooking the shield wires to ground had no effect. Both codes reappear. The junction J2 where a few shield grounds come together is next to the glove box light according to FSM. All I see there is a two wire connector plugged into a yellow loom with a single multi element cable. I will look further a little later. The previous owner was running an audio amp. The negative battery cable was melted on the side going to the body ground. Any ideas on the next place to look? Thanks

I think we need to step back. The shielded wires are there to protect the wiring so it doesn't pick up any other RF signals because the PCM needs as clean a signal as possible. So the shielding is not there for ground. If you look at your diagram I circled the ground locations. This is after the sensor. So the shielding portion where I put pointers, is the shielded part because this is the signal wires to the PCM.

I attached the diag for these codes. Basically it is telling you that the PCM is not getting a signal from either sensor. So that means there is either an issue with the sensor or the wiring. The fact that you have 30 ohms of resistance on these wires is what we need to address.

What I would suggest is trying to run new wires from the sensor to the PCM. Don't worry about using shielded wiring at this point. You just want to prove out that it is wiring.

Thanks, I was not sure of my next step. I will put new wire from Knock Sensor connector to ECM and test drive.

Hi, so I connected two new wires from the Knock Sensor connector(4 pin) to the ECM (cut existing wires) pins E7- 15 and 14. Codes took longer but came back. I hooked those wires up to scope meter and ground. I set on AC voltage and took both sensors at 4000 rpm. Here are the hold's. I am not sure how to make the wave more visible, this meter is new to me.

One thing about my meter, when I test an outlet in my house, It reads correct numbers and allows making the wave visible in a few different scales
Is there a way to donate to you? I don't see a link for it. Thanks

When you connected those wires, did you cut the other ones so that you were only running on the new wires or did you just overlay them?

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Hi, yes I cut the wires at the ECM. Do you think the 4.3kHz I was getting at 4,000 rpm's is actual? Should I open up the intake manifold again and replace sensors? I bought a few sensors the latest are marked Denso for $40.00 each. Should I pay $170.00 each for Toyota sensors? What do you think?

It is possible. Basically hertz readings are measurements we use for measuring AC signals or bandwidths of digital signals. We also use it for measuring vibrations and the knock sensor is used to measure vibrations in the engine that the PCM will interpreter as engine knocking so it can adjust fuel to try to get rid of the knocking. If you are running the engine at 4000 RPM and you are getting 4300 hertz, I would expect to see that. I have never done this so I could be wrong but just from what I am seeing, I don't think that is an issue.

As for the sensors, that is a hard call and I am not sure I would do it. Clearly the Toyota sensor is of better quality but I doubt these other sensors would trip this code out of the box like this. At least not multiples of them. Maybe I would get one of them and if the code goes away on that side I would get the other.

Problem with easily testing these sensors on the 1MZ-FE engine. The plenum and the intake manifold both have to be removed. $300.00 to $400.00 job.plus $50.00 in gaskets.

Rock and a hard place. I will tell you what, I will ask the other guys to review this post and see if I am missing something. I read through it again but it is late so maybe I am making an assumption that is wrong.

If both sensors are new. and the code wont clear. try cleaning the pig tail connector of any corrosion. If it is not making good connection or the connectors are loose causing the issue. You may have to try to use a pick and bend the connector tighter if you can take it apart with out braking it or buy a new connector.

Thanks you guys. Appreciate all your input.

when i worked in engineering i worked with motors among other things we had a few engine returned to us that were down on power what it turned out to be was metal shields around the knock sensors the bolts holding the shields were not tightened at the factory so the shields were loose and rattled setting off the knock sensors. check for anything like that aloose bracket, shield etc. you have no idea what this man has done prior to even checking for the codes. As true as things are you as a mechanic know that people don't always give you the complete story.

Thanks, I will look. Actually I am doing the labor myself. Bummer, now I have to do it again.

Thanks everyone for jumping in. Keep us posted with what you find. Thanks