TPS and Knock Sensor Codes

Ok, as you might remember i had the dealership replace both of my knock sensors and pigtail harness after i was getting a knock sensor bank 2 code on my 2002 1500 4.8 4L60E. So it has been about a week and a half and i was driving home from work and my SES light came back on, so i go past the dealership i had the work done on my way home from work every day, so i stopped in to see if they could just scan it for me and see if it happened to be the same code. Well the service manager was the only one left in service when i got there and he told me that "he didnt know how to run the scanner. And that he could do very little" WTF is that! Your a GM service manager and you dont know how to run a scanner! Anyway! So i went and bought a good scanner and scanned it myself. (heck at this point i could be the GM service manager) I forgot to write down the codes, so sorry. But this is what i got. I got a TPS code, and a knock sensor bank 1 low input code. And i just had both of the knock sensors replaced. So I cleared the codes (thats why i dont have the number, i hurried up and cleared them in the parking lot). After i cleared the codes the drive home was the best my truck has ever run and shifted since i got it! It seemed to run up RPMS higher before it shifted and it ran so nice! So when i got home i pulled the TPS and checked it cause i just put it on about two months ago. It seemed fine, I pulled the IAC and cleaned it cause it was built up with carbon, and readjusted it. I reinstalled everything and checked for codes and there was nothing, ran it down the road and it was fine. (It didnt run as perfect as it did right after i cleared the codes, but it still runs good) Drove it to work today and it was fine, so what the heck was those codes for. Also how many warm up cycles would it take to bring those codes back if it was a problem. I would have thought they would have come right back on if there was a problem. So im going to run it and see if the light comes back on and get the codes again if it happens. Could it just have been some sort of false reading? Thanks for the input.

We would need the code no.
Codes do not say replace parts but to check it out.
You need to go threw the repair flow chart for that code no.
On the knock sensor code there is a tsb on it for known problems on wiring and moisture getting to knock sensors.
They are under the intake and have a lot of wiring problems and get moisture down in the sensor holes.
Have you washed off the engine.

If code does not come back all is well.

But if it comes back and resets light get it back to the dealer and have the lick there calf over.
MT

No, i havent washed the engine, and it hasnt even barely been driven in wet conditions since i had them replaced. I even installed extension flaps in the wheel wells to keep water from getting in through the wheel wells. The dealership is going to call me today about it since the "Service Manager" couldnt really do anything for me yesterday. But the good thing is that there is a 12 month 12,000 mile warranty on parts and labor from the dealership. Ill see if the code comes back and if it does i will write it down and let you guys know. But if there was a real problem wouldnt the SES light come back on after i cleared it? Road conditions and weather conditions would have been the same from when the light came on to when i cleared it an hour later when i drove it. Thanks!

Yes and no on engine light.
If there is a problem and it stays a problem it will set the light.
But if it is coming and going like a loose conection or fixing it self it may not turn the light on.
That is where you need a good engine capable scanner and a good tech/mechanic to check for present and ALSO HISTORY CODES.
and read out sensors.
Take it back and let them check it out.
Good Luck
MT

Could a gunked up IAC throw off a TPS and Knock Sensor cause when i pulled the IAC off there was a crusted ring of built up carbon on the pintle of the IAC, which i cleaned off and actually had to scrape it off with my finger nail. Just wondering if that could do anything. Also my scanner has the ability to read out sensors, dont know if it reads out on all or even the ones that need to be checked. Just some more information.

No on dirty IAC but a good idea to clean TBI buttery fly and IAC valve with carb or TB cleaner and plastic tooth brush for better idle.
The TPS sensor voltage is complicated on that one.
It is a double sensor with two sets of voltage reading.
One pull down reading and one pull up voltage.
Knock sensors are better checked with a ohm reading on a volt/ohm meter.

For a interminent code or check engine light run a ford type wire wiggle test on it with scanner hooked up.

If you are going to get very far into it.
You need to get a factory repair manual or a all DAT sub.

http://www.alldata.com/products/diy/index.html
It gives you all of the test and specs for running a repair flow chart on what ever code you get.
Good Luck
MT

Ok, it didnt take very long for the SES light to come back on, came on again on my way home from work last night, code was P0327 Knock Sensor 1 low input. Called the dealership and they had me bring it right down so the technician who fixed my truck the first time could test the knock sensors (OHM them from the pigtail) He checked the ohms on the knock sensors and said they were putting out what they should be, both of them. So now he is saying that it looks like it could be a problem with either the wires from the knock sensors to the computer or something with the computer. What do you guys think? I checked all connections at the computer and at the pigtail for the knock sensors and tried the wiggle test on computer and sensor wires while the scanner was hooked up. I also had the scanner check the memory in the computer and it all passed. I cleared the code last night, and hoping that it comes back on today cause im taking it back to the dealership tommorow to check it out again.

Code P0327 is a problem on front knock sensor or wiring circuit or computer.
To test of specs. The OHM test is 93-107 ohms.
They then need to set the OHM meter to 400 mV AC scale and tap the engine block to see if the sensor is working.
If it is working you will get a signal at that setting on the Ohm meter.
If ohm checks out and the sensor if producing a signal at 400 mV AC scale on ohm meter or a good signal on a lab scope.
Check wiring and wiring circuit to PCM. if all of that is good the problem is in computer.

Drive it enought to get the code back on before you take it in.
It may help them check it out.
And ask them what code you had to start with before they worked on it.
Let us know how it goes.
Good luck
MT

If it gets down to a computer problem you may have a 70K or 7 year federal emmisions warranty on it or calf. may be longer.
Good luck and let us know how it goes.
MT

I just checked the Warranty booklet in my truck and online. VCM, PCM, and BCM are covered for 8 years or 80,000 miles. That would be great! cause mine is only 6 1/2 years old and 61,000 miles. Im glas you brought that to my attention. Im will talk to them about it cause im sure they wouldnt have told me if I didnt ask. Also it said something about not passing emissions to be covered, we dont have emissions. So would it just be covered. Thanks again.

Took it into the shop this morning, talked to the service manager and he said ya if its the PCM its a 8 yr 80k mile warranty. I cant get the code to come back. I drove it for like around 100 miles and no light, so i just told them the code that was being thrown every other time (P0327). Im hoping they find something, i just dont think my truck is running right, after i cleared the code monday night and drove it, it was like a completely different truck! then after i shut it off and turned it back on it was back to the way it has been, it runs ok, just not like i think it should. Also i think there might be something wrong cause im getting under 12.5 MPG. I think thats insane for a 4.8. I do have 285 tires on but still i think i should be getting around 15 city.

I checked the knock sensors myself last night. one check out at 103 ohms and the other checked out at 104 ohms. Then when i would tap on the block they would jump up to somewhere around 120. So im assuming that is what they are supposed to do. And i wasnt taping very hard either. So ill have to wait and see what becomes of this problem. i really hope they find something with the computer cause i feel my truck should be running alot better than it actually is. Thanks guys!

Yes it should do better on MPG.
Sounds like it is in good hands.
We hope they can find the problem and also help gas mileage.
Good Luck and Let us know how it goes.
MT

Ok, good news! The dealership called me and said that they will have to replace the PCM because the technician that has been doing all the work on my truck concluded that the PCM was shorted out in the area that controls or takes data from the knock sensors and that it will all be covered under the 8yr 80k Federal Emissions Warranty. That is awesome! They are also taking care of a recall on speed sensors or something like that, which i thought would have been taken care of when the truck supposedly went through the shop right before i bought it. But oh well i should get my truck back tommorow and hopefully its runs like i have never felt it run before with better gas mileage too. Thanks ill let you guys know how it goes!

You are welcome.
That sounds like a winner on the 8 year 80K emmision warranty on PVM/VCM.
May even help gas mileage.
Cats are covered under same warranty.
Good luck and let us know how it goes.
MT

I cant wait to feel what it runs like cause it has run like this since i got it in October and i just thought thats the way it was supposed to run. But if the computer was bad or just not seeing knock sensors at all then it is probably running not so good. Im hoping that the truck runs like it did the one time i drove it for a couple minutes after i cleared the codes monday night, cause it was awesome!

Got my truck back on friday afternoon, no check engine light, runs good, shifts a little better. Doesnt run as better as i thought it would, but runs good. I can tell a difference. Im still getting a slight surge during an acceleration, like real slightly like you can barely feel it, the truck quits accelerating and then it kicks in again and goes, these feelings are very slight, and it did it before all of this, but i thought it would go away, and it doesnt do it all the time. I also just for the heck of it scanned the truck again yesterday and i still got a PO327 knock sensor low input circut bank 1, but it was pending, but that still doesnt look right to me, if they said the problem was in the computer and they replaced the computer then why would i even get a pending code that was the same as it was before. And how long do i have to drive it for it to relearn itself pretty good? Thanks!

Taking it back to get it worked on again this week, check engine light came on on my way home from work last night, same code. Stopped and talked with the technician and he said that the one knock sensor they put in wasnt a GM sensor it was an aftermarket, so they are going to order a GM one and replace the after market one with a GM one. This is becomeing a pain in the butt!

At the shop today, ill let you know how it goes.

Got my truck back last night. They even detailed the whole thing for having it in three times. Anyway, it is deffinately better. And im hoping to get some better gas mileage out of it also.

Got my truck back last night. They even detailed the whole thing for having it in three times. Anyway, it is deffinately better. And im hoping to get some better gas mileage out of it also.

what was the problem that they finally repaired ????

do you think they may have not replaced the knock sensors and just tried to clean up the connections or some other trick.....?


hopefully they put a oscillascope on those sensors to ensure the output is clean sine wave...

Hey man I found the knock sensor is a real problem. Clearing codes is a temporaley fix. The knock sensor is a microphone it will hear alot of things. one thing I hope it is not hearing is the wrist pin knock that you may or may not hear. If it is the wrist pin knock ( everybody else calles it the piston slap) ( cold knock) what ever,then it will not matter what you do. The darn thing will keep coming on. Some people say put silicone around the sensor to help with the moisture, and buffer its ability to hear good. But that wont fix the wrist pin. And yes clearing the codes sure makes the performance better

There are two knock sensors under the intake, Why your dealer did not change both while they were there is appaling. I would not want them to keep pulling bolts is and out of the aluminum heads.

They did replace both sensors back 3 weeks ago, but they were having a hard time finding the second sensor the day of repair and they didnt want to leave sit open over the weekend and have to order one, so they finally found one. What they didnt tell me is that it wasnt a GM sensor for the second one they replaced, so i got 1 GM and 1 aftermarket sensor, and the aftermarket one is the one that that wasnt reading right. So now all seems better. no codes. But one thing is when it is wet or raining out i get a slight surge like i talked about before, ill make a new post.

Another thing about knock sensors is that they arent going to throw a code like i got because they are picking up knocks, thats what they are supposed to do, when it picks up knocks it retards the timing, you get codes like i got when the knock sensor(s) are going bad. So i shouldnt get that code all the time as long as my knock sensors are good. i might get less performance from it picking up the piston slap knock, but i shouldnt get a code of malfunctioning knock sensor.

[quote=xjcamaro89]They did replace both sensors back 3 weeks ago, but they were having a hard time finding the second sensor the day of repair and they didnt want to leave sit open over the weekend and have to order one, so they finally found one. What they didnt tell me is that it wasnt a GM sensor for the second one they replaced, so i got 1 GM and 1 aftermarket sensor, and the aftermarket one is the one that that wasnt reading right. So now all seems better. no codes. But one thing is when it is wet or raining out i get a slight surge like i talked about before, ill make a new post.[/quot
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thanks for that info now this is what i thought....these knock sensors are very critical in the proper engine computer timing control....to put non oem sensors is a no no but the dealer did it so this is why i don't trust the dealers judgment when they do stupid things like this....which is why I stated to you to make sure you get written warrantee........

I did get a written warrantee, and i havent paid for the last 2 visits to the dealership just the initial cost the first time to get the 2 knock sensors replaced cause i remembered you said that before and i made sure i had something in writing before i left.

Ok, the truck has been running progressively better of the past couple days, im thinking its just the computer relearning itself. I really hope to get some better mileage now. Thanks for all your guys help on here!

Ok, its been 2 weeks almost since i got everything all figured out and replaced with the right stuff. Since then i have ran through a tank of gas and filled up saturday. Before i got the knock sensor replaced i was getting 12.5 MPG, the first tank i ran after the fix i got just under 15. Which to me sounds alot better, 2 to almost 2.5 MPG better. I can drive for over two weeks on a tank of gas, thanks again for everyones input!