How to Replace/Repair Knock Sensor Wiring?

[TheManOutside]

Hello! First of all, i wanna say that i am not "mechanically challenged," however, when it comes to wiring i have no idea what i'm doing. I have also done tons of research and just can't find anything helpful to me. "Oh just check the continuity then bla bla bla" (????)

i have a 1985 4runner with the CEL light on, giving me code 12 (knock sensor). I have replaced the sensor, and still have the code. i don't think the ecu is the problem, which means the only other thing it could be (as far as i know) is the wiring. the CEL only comes on at ~2-3k revs, it runs fine until then, so i do not think the engine is actually knocking.

so, what do i need to get, and what do i do? I was given a link to this wiring, it's just i have no idea what to do with this haha. i need as much help as possible because i really have no idea what i'm doing :bounce: thanks!

i was also told to check the continuity of the wire, but i have no clue how to do that either (although i do have a multimeter! which i think is a good thing?).

 

[GHARP57]

the sensor wire is about a foot long its like 30 bucks or so from the dealer. Usually when you replace the sensor just go ahead and replace the wire, usually after so many years its better to replace it when you do the knock sensor

 

[flyinhawaiian01]

I see your tag says you have an '85 4runner, which means you should have a 22RE and not the 3VZE, correct?

First things first, what brand of knock sensor do you have? Is it oem or at the very least a good quality brand like Denso?

I'm leaning towards either an incorrect knock sensor or one that doesn't want to play nice with the ecu. You say it only comes on at 2 or 3k rpm, so that tells me it is not the wiring and the ecu IS seeing the signal.

This has been reported a few times now, and IIRC, about 2 weeks ago someone replaced one on a 3vze that didn't work, he then replaced with an oem, no other work done to the vehicle, and all was well again.

I don't know if the two engines shared the same knock sensor or if they were different part numbers, and its quite possible that someone looked up the wrong engine and gave you the incorrect part.

As for the wiring, the 22re is not the same as the 3vze. The 3vze has a short cable to connect to the main harness, or something like that, whereas the 22re runs directly from the ecu to the knock sensor, so its important to know which engine we're dealing with first.

If it is the wiring, unless your harness is torn up or damaged, check the connector itself to the knock sensor, that's usually where it would go bad since its the only part that's really exposed. Look for frayed wires at the yellow plug that connects to the sensor, see if its clean inside the connector and if not, clean out with brake clean and put some dielectric grease directly into the tip.

You can also check the ground on the engine if nothing else helps. If you just want to test this, use a pair of jumper cables, connect direct to negative terminal on battery to somewhere on the block, tie/bungee/tape up the rest of the cable so it doesn't dangle, take it out for a ride (reset the code first!) see if it comes back.

I failed smog once because the ground cable wasn't secured to the block and the o2 sensor wasn't able to complete its circuit! A solid 4awg cable from block to battery cleared it all up and passed smog! The knock sensor will need the same return and uses the block as its return line to complete its circuit.

 

[KidVermicious]

FWIW, the 22RE isn't known to have trouble with the knock sensor wiring, not the way the 3VZE does. Unless there's visible damage to the sheath, I'd verify the part too before hacking up the harness.

 

[TheManOutside]

I see your tag says you have an '85 4runner, which means you should have a 22RE and not the 3VZE, correct?

First things first, what brand of knock sensor do you have? Is it oem or at the very least a good quality brand like Denso?

I'm leaning towards either an incorrect knock sensor or one that doesn't want to play nice with the ecu. You say it only comes on at 2 or 3k rpm, so that tells me it is not the wiring and the ecu IS seeing the signal.

This has been reported a few times now, and IIRC, about 2 weeks ago someone replaced one on a 3vze that didn't work, he then replaced with an oem, no other work done to the vehicle, and all was well again.

I don't know if the two engines shared the same knock sensor or if they were different part numbers, and its quite possible that someone looked up the wrong engine and gave you the incorrect part.

As for the wiring, the 22re is not the same as the 3vze. The 3vze has a short cable to connect to the main harness, or something like that, whereas the 22re runs directly from the ecu to the knock sensor, so its important to know which engine we're dealing with first.

If it is the wiring, unless your harness is torn up or damaged, check the connector itself to the knock sensor, that's usually where it would go bad since its the only part that's really exposed. Look for frayed wires at the yellow plug that connects to the sensor, see if its clean inside the connector and if not, clean out with brake clean and put some dielectric grease directly into the tip.

Yeah, I have a 22re. I really should have specified that, my bad! I'm not sure if it is OEM or not, but I do know that it was pulled from a 1986 4runner with a 22re.

FWIW, the 22RE isn't known to have trouble with the knock sensor wiring, not the way the 3VZE does. Unless there's visible damage to the sheath, I'd verify the part too before hacking up the harness.

I'm not currently home, but I am pretty sure the wiring LOOKS fine, but I will check. I did clean the connectors, maybe not good enough?

As for the actual sensor, this is a pic of my old (left) and new (right) ones.

The new one does look different, but it fit in place fine. You can't see it in the pic, but there is a little triangle/arrow logo looking thing on it (kinda like the "recycle" symbol, if that makes sense).

I was having tranny issues, so I sent my truck in to get it rebuilt and I told the guy about the sensor. He told me it was the wiring harness (i have a strong feeling he half-assed the diagnoses though lol). He also told me he couldn't fix it for whatever reason so idk.

 

[flyinhawaiian01]

Well, there's really no way to test the knock sensor, aside from just making sure there's no continuity between the plug and the housing.

A knock sensor is basically a little microphone that listens to the sound, and when it hears what we know as detonation, or knock, it "stimulates the mic and the mic sends out an AC type of electrical signal. Now, if you have an oscilloscope, then you could test it to see if it hears the engine running, but most folks don't have one of them layin' around their home!

So, grab your multimeter, see if it has a continuity or ohms setting (look for the symbol Ω), stick one lead into the plug, touch the other lead to the body of the sensor, and see if it reads anything. If it beeps or says there's resistance, the sensor is most likely bad. If it doesn't show anything (just like it would be if you didn't touch the leads together at all), then it may be correct.

Here's the problem, we still don't know if that sensor is really working correctly for that engine. Knock sensors should be "tuned" for the sound frequency of a specific type of engine. A knock sound is totally different in a 4 cylinder engine than it would be for, say a big block V8.

A quick rockauto part number check showed me that the 4 cylinder knock sensor looks like the one on the left in your photo, yet the right one looks identical to the 6 cylinder knock sensor for a few 6 cylinder engines. If you click the part number in rock auto, it will show you a listing of all vehicles that use the same part number. The one on the right works for the 3VZE and the 5MGE ('85 supra, which is exactly what I have) engines, and the one on the left are for 22RE engines, including the '85 celica (which also had a 22re)!

I have a feeling the one you got is for a 3vze, whether someone put the wrong one in the engine you got it off of at the junkyard, or the engine you got it from was a v6 and you thought they were the same (pretty common mistake I guess, as I've seen this pop up on a few searches I just did), it looks like you'll ultimately need to get another one to really test this out.

If you know anyone with a 22re who's willing to unscrew it and let you test it out, that would be the easiest way. Luckily, its easy enough to get to and testing it will literally take just a few minutes to do.

Unfortunately, they are expensive to buy, even those that are not oem, so I'd be looking into the buddy program here and borrow one to test! Remember, electrical parts are not normally returnable if you find that wasn't the problem!!!

 

[TheManOutside]

So, grab your multimeter, see if it has a continuity or ohms setting (look for the symbol Ω), stick one lead into the plug, touch the other lead to the body of the sensor, and see if it reads anything. If it beeps or says there's resistance, the sensor is most likely bad. If it doesn't show anything (just like it would be if you didn't touch the leads together at all), then it may be correct.

Here's the problem, we still don't know if that sensor is really working correctly for that engine. Knock sensors should be "tuned" for the sound frequency of a specific type of engine. A knock sound is totally different in a 4 cylinder engine than it would be for, say a big block V8.

A quick rockauto part number check showed me that the 4 cylinder knock sensor looks like the one on the left in your photo, yet the right one looks identical to the 6 cylinder knock sensor for a few 6 cylinder engines. If you click the part number in rock auto, it will show you a listing of all vehicles that use the same part number. The one on the right works for the 3VZE and the 5MGE ('85 supra, which is exactly what I have) engines, and the one on the left are for 22RE engines, including the '85 celica (which also had a 22re)!

I have a feeling the one you got is for a 3vze, whether someone put the wrong one in the engine you got it off of at the junkyard, or the engine you got it from was a v6 and you thought they were the same (pretty common mistake I guess, as I've seen this pop up on a few searches I just did), it looks like you'll ultimately need to get another one to really test this out.

If you know anyone with a 22re who's willing to unscrew it and let you test it out, that would be the easiest way. Luckily, its easy enough to get to and testing it will literally take just a few minutes to do.

Unfortunately, they are expensive to buy, even those that are not oem, so I'd be looking into the buddy program here and borrow one to test! Remember, electrical parts are not normally returnable if you find that wasn't the problem!!!

Thank you for explaining the continuity thing for me. I will test it when I get to my truck this weekend. I was looking on rock auto originally, but that price tag turned me to get a used one (i only paid like $45). I will post back here once I test the continuity.

 

[TheManOutside]

So, I checked my continuity today, and the multimeter stayed at 0.. So, doesn't that mean everything should be working? What do i do now?

 

[TheManOutside]

:bump2:

 

[TheManOutside]

is it possible an exhaust leak could cause this issue (I wouldn't think so but who knows). otherwise, I'm guessing my truck is just screwed...?

 

[TheManOutside]

anyone?

 

[flyinhawaiian01]

I've been on vacation since the 27th, and just saw your bump!

While you read 0 ohms from the sensor, it still doesn't mean that its working correctly. I know that my 1uz sensor looks exactly like it, but I doubt it would ever work properly for the 22re. Both should read 0 ohms, but neither are really interchangeable.

Only way to find out if it works correctly requires an oscilloscope while the engine is running to determine whether its "listening" correctly, and I doubt you have one.

This brings you back to either borrowing one off a 22re engine that isn't throwing that code, or buying an OEM sensor to replace it, or putting your sensor into another 22re and see if it throws that code. Pretty easy to find a 22re vehicle in Cali, perhaps a neighbor or friend has one that wouldn't mind some free beer and/or pizza as you turn his vehicle into a guinea pig!

 

[TheManOutside]

I've been on vacation since the 27th, and just saw your bump!

While you read 0 ohms from the sensor, it still doesn't mean that its working correctly. I know that my 1uz sensor looks exactly like it, but I doubt it would ever work properly for the 22re. Both should read 0 ohms, but neither are really interchangeable.

Only way to find out if it works correctly requires an oscilloscope while the engine is running to determine whether its "listening" correctly, and I doubt you have one.

This brings you back to either borrowing one off a 22re engine that isn't throwing that code, or buying an OEM sensor to replace it, or putting your sensor into another 22re and see if it throws that code. Pretty easy to find a 22re vehicle in Cali, perhaps a neighbor or friend has one that wouldn't mind some free beer and/or pizza as you turn his vehicle into a guinea pig!

No worries!

One of my friends has an 89 pickup with a 22re, I'll see if I can get him to let me test his sensor out sometime

 

[almost4rn]

Dont mean to bump a pretty old thread.. But did you ever get this fixed?? Im having the same exact issues after i dropped in a new longblock on my same head. It was fine and then out of nowhere started throwing that code 12

 

[TheManOutside]

Dont mean to bump a pretty old thread.. But did you ever get this fixed?? Im having the same exact issues after i dropped in a new longblock on my same head. It was fine and then out of nowhere started throwing that code 12

I actually did get this fixed! There is a metal insulation that goes around the wire that is completely unnecessary. Follow the wire back to the ECU and see if the insulation goes all the way to where the wire connects to the ECU. If it does, simply cut the insulation right before it goes into the ECU. This insulation can ground itself to the ECU (which it's not supposed to do), so cutting it stops it from doing that and stops the code from being thrown. I fixed this about 4 months ago and haven't had a problem since.

TLDR; cut the knock sensors wire insulation so that it does not connect to the ECU.

 

[almost4rn]

This is where i'm slightly confused, because it seems like my wiring doesn't have insulation at all... Its a black cable inside of a rubber sheath, but it doesn't look insulated what so ever..

From looking at the FSM guide, the pin on the ecu is in the middle harness, second from the right, on the top... But its a different colored wire (Black with purple dots)? and it doesn't seem to have any insulation there at all either.

None of the wires connecting to my ecu seem to be insulated..

So frustrating because its in limp mode, gas sucks and so does acceleration with a brand new block


BTW i have an 85 4runner sr5. So pretty much the same truck. So confused, think i might to to the junkyard and maybe pull some wires or a knock sensor if i can find one..

 

[kc15842]

I have a 3.0 and battled the original wiring harness so I ended up buying shielded cable and toyota connectors and made a new NS harness. I made an extra harness and have an extra KN if you want to try it. Where in Cali? The limp mode SUCKS!

 

[almost4rn]

I have a 3.0 and battled the original wiring harness so I ended up buying shielded cable and toyota connectors and made a new NS harness. I made an extra harness and have an extra KN if you want to try it. Where in Cali? The limp mode SUCKS!

Dude that would be sweet! Do you know what year the knock sensor is from? Correct me if i'm wrong, but i heard you need the same knock sensor year as your ecu?

But that would definitely be worth it to test, as It's impossible to find a 22re at a pick n pull. I live in North bay area, in petaluma

 

[kc15842]

Ks

Here is the KN and wiring. You would need to remove the pins from the KS connector and then at the controller. There is a ground bundle that needs to be peeled back and the ground connected.

 

[almost4rn]

is this for the 3.0? Cause i don't think the knock sensor will work, but im sure i could get the wiring to work though.

Its strange though because my sensor wire doesnt look grounded at all! its not a thick cable or anything, just a regular wire from what it looks like.