Does anyone know how I can mod the wiring of the two sensors to read from just one? I can't shake this code, regardless of new AC Delco sensors and harness. I did the job correctly, sealed covers AND built dam around the rear one, too, and of course installed new Felpro intake manifold gaskets. Threw the code again 5 miles later after repair.

Tested continuity of the new sensors via new harness, as well as continuity of main harness. At wit's end.

I understand what knock sensors do, which is why I am not looking to bypass them entirely. I also understand that the code means low voltage signal to PCM, and am pretty sure the code was meant as a means to know when a knock sensor fails. But in this case, like many other I've read about on the GM engines in all sorts of vehicles, this code can plague you even if knock sensors and wiring are all good. If only I could get rid of that test-for-voltage code snippet, but obviously I can't.

So, at this point I am looking to bypass the rear sensor. While simply splitting the front wire to the main harness connector sounds easy enough, I suspect there is more to it than that.

Any electrical engineers lend a hand here? Do I need a capacitor or something after the spilt to isolate the signals from each other before the split wires meet the main harness connector?

Any help in this regard would be greatly appreciated.

 

My brain is fried over this right now, and at this time I can't remember all of what I checked. Everything is back together, so the only thing I can check now for continuity is from the point where the sensor harness connects to the main harness.

To be sure I understand what you're saying, you want me to check continuity of the wire for the rear sensor, but in the main harness. To do this, I would disconnect the sensor connector at the main harness, then test from the top wire (top wire connects to rear sensor) in the main harness connector to pin 11 in the connector at the PCM, correct?

 

if you have hptuners you can turn the sensors off but I wouldn't do it if it were my car

 

Just double-checked. Checked front, too, for comparison. Same good reading. No opens.

 

I already said I didn't want to bypass them altogether.

 

well you can turn one off, I still wouldn't do it though

 

I may have miscommunicated in my first message, so let me elaborate and rephrase a bit.

​​​​​​I had a rear sensor code. Upon removing them, the rear was corroded, while the front looked like new even with 180k miles of it. After replacement, I still have the code.

Here's something that puzzles me: While some people say they tested their sensors, I don't know what they did, becauze the pin that you plug the harness onto is isolated from the rest of the sensor. This, I could clearly see by looking closely at the old good one I took out. I put a meter on it, and I get no ohm reading, as expected by the floating pin design.

It strikes me as odd that the code refers to low voltage, when I can see that if the insulation fails, the floating pin would touch the body and create a resistance reading that's higher than 0. Well, maybe that's what it does mean, as higher resistance = lower voltage, right?

Anyway, the only results I can see from testing in the car is that I get a 0 ohm reading when the car is off, which makes sense given what I am seeing with the old good sensor. Testing for continuity on the harness to the sensors, I get 0 readings on both.

Maybe I am testing wrong, I don't know, but if so, somebody please tell me.

And, what are the chances that I happened to get one good sensor, and one bad, and put the bad one in the same place as the bad one I had? If the odds are 50/50, I don't want to keep throwing sensors at the problem, as they sure aren't cheap! I used ac delco sensors, if that matters.

The vehicle runs stronger than ever now, which I believe is due to the the new Manifold gaskets and the fact that the pinging I was hearing when the old rear sensor was bad is now gone. It acts like it's working fine now, aside from the low voltage code.

Hence, my recent thoughts to just bypass the rear sensor. After all, when the rear one died, when I got ping, it would go away while driving, and I got bad gas mileage, so I figure the front one was taking care of things by itself.

Ideally, I wish I could make the PCM not look for the low voltage error. I would live with that, at least, because of what I am dealing with. I thought I read something about that somewhere but am not sure. Do you know? Or, have other suggestions?

 

OK, I am officially an idiot!

When testing the sensors for resistance, I had the ohm scale set too low. I thought I was looking for 100 ohms or so, when I should have been looking for 100,000 ohms.

Once I moved the range up to 200k, I saw a reading on my old good sensor of 100k ohms.

I just went out to the car and checked. Sure enough, the new front sensor reads 100k ohms, while the new rear one doesn't read at all, not even at 2M range. Either there is something wrong with the new harness or the new sensor.

If it's the sensor, should I re-use my old good one with 180k on it? If I re-use the old good one, I can be up and running quite quickly, and not chance getting another bad one, which might, in fact, be a common problem even getting AC Delco. Should I go to a store with my meter and test to find a good one? I got the ones I bought off Amazon for like $45 each, but with something like this, I guess it pays to buy local. Too bad, because they were half the price on Amazon, but having to take the manifold off again was not worth the savings.

Maybe I will get lucky, and it's only a bad harness. In either case, now that I know what I know, I would highly recommend that EVERYONE have a multi-meter for this job so they can test every new part beforehand before proceeding with this particular fix! So, if you have no multi-meter, you should not attempt this job!