GM Knock sensors - installed but still CEL

[Too Bzy]

Hey guys, been a while since I posted. First of all let me say Gabe is the man and I appreciate all he's done for the community and in the way of customer service. Secondly, I received my knock sensors from him and had my mechanic (Toyota only man for over 20 years) install them and the check engine light came back on faster than it did before the install! Need some help before we take the whole car apart again and install either new ones from Gabe or factory. Is there anyway to check the GM ones or any trouble shooting I can do before we take this all apart? Any help or ideas would be appreciated.

[trd4life]

Hey guys yeah i need some help here. I suggested he change the knock harness which he already did, the sensors were brand new. its weird i have never had anyone with any issues with these at all. what should we do next can we test them?


thanks

gabe

[SolaraPete]

I assume your tech cleared the CEL with a scanner or by disconnecting the battery after you installed the new sensors?

[02slera]

i thought there was a wiring mod you could do at the computer.
as i remember there is a front sensor and rear sensor, and the front causes problems the quickest, so the mod was to make the computer receive both signals for front and rear from only the rear sensor.
its hard to believe both the gm sensors you received are bad, so if nothing else, this wiring method could be used to make the car work with one sensor or the other, and verify which one is throwing the cel.
you'll have to search the forum for more info on this, its definitely on here though. good luck.

[SirThomas88]

He probably wants two functional knock sensors.

as i remember there is a front sensor and rear sensor, and the front causes problems the quickest, so the mod was to make the computer receive both signals for front and rear from only the rear sensor.

I think it's the other way around. the rear knock sensor (sensor# 2?) gets more vibration and fails first. That's why you often see relocated knock sensors that are near the back of the engine.

[02slera]

ok im not sure about how it was wired or which sensor was which, but just wanted to give the idea so if it seemed worth it to the op he could look it up and get the details. Still, if two sensors are desired to be operational, the wiring technique may be used as a means of troubleshooting if no one else has a better way to test the knock sensors.

[hskrsolara]

He probably wants two functional knock sensors.

as i remember there is a front sensor and rear sensor, and the front causes problems the quickest, so the mod was to make the computer receive both signals for front and rear from only the rear sensor.

I think it's the other way around. the rear knock sensor (sensor# 2?) gets more vibration and fails first. That's why you often see relocated knock sensors that are near the back of the engine.

correct, the rear knock sensor always blows first (firewall side). I had problems with mine and found out the wiring was loose. Soldered them up, no more problems. I would check for proper installation before giving up on them. it is damn near impossible to blow the GM sensors in our setup. you can override the rear (firewall) sensor too, I believe Vik (dawgz) did this, talk to him if you would rather trick the ecu than pull everything apart to rewire your sensors.

[Too Bzy]

Yes, we cleared the codes, cause they came back faster than they did with the faulty original ones. He tested the OG ones and found that one of them was bad but because these are GM, he doesn't know how to test these. I was just looking at AKORA's relocation (actually in his for sale thread) of a sensor but is that the back sensor and he did the mod at the computer or just relocation of one sensor?

[Eye8Pussies]

the first thing that we need from you is more information actually....first off, which sensor was it that was throwing the CELs in the first place?

And now that you've changed the sensors AND the harness, what CELs are you throwing? the same as before? both? one? front? rear?

Do the CELs come on IMMEDIATELY? as in, you turn on the car, rev up the engine, or drive half a block and then they come on? or do they come on after a short drive? differences in symptoms need to be described in order to help you troubleshoot your problem


to also help people clarify the "inherent" knock sensor issues that the 1mz seems to have:
- the front bank sensor (which is the firewall side), seems to spontaneously go bad or throw codes due to the vibrations or something, caused by the supercharger
- the rear bank sensor (which is the radiator side), seems to go bad or throw codes due to the lack of fuel in the rear bank fuel rails since, for the gen4 and solara, it's a non-return style fuel system, and the front bank can potentially take all the fuel - this problem is mostly solved by installing Jim's Fuel mod

[Too Bzy]

the first thing that we need from you is more information actually....first off, which sensor was it that was throwing the CELs in the first place?

And now that you've changed the sensors AND the harness, what CELs are you throwing? the same as before? both? one? front? rear?

Do the CELs come on IMMEDIATELY? as in, you turn on the car, rev up the engine, or drive half a block and then they come on? or do they come on after a short drive? differences in symptoms need to be described in order to help you troubleshoot your problem


to also help people clarify the "inherent" knock sensor issues that the 1mz seems to have:
- the front bank sensor (which is the firewall side), seems to spontaneously go bad or throw codes due to the vibrations or something, caused by the supercharger
- the rear bank sensor (which is the radiator side), seems to go bad or throw codes due to the lack of fuel in the rear bank fuel rails since, for the gen4 and solara, it's a non-return style fuel system, and the front bank can potentially take all the fuel - this problem is mostly solved by installing Jim's Fuel mod

The sensor were checked after they were pulled out and one was found to be bad. I think they come on right away as in after you turn on the car. The codes don't say which one and that's wierd. Also we didn't change the harness but installed them as per the instructions that came from Gabe. I haven't heard before that the harness needed to be changed.

[trd4life]

Your mechanic told me he did use a new knock harness on your car.

[Too Bzy]

Yeah, I found that out too Gabe, thanks for the other information. He's checking into how to check the sensors now.