Wont go into CL - FTs Zero / O2 Reading 440-450mv

[WS6_LOU]

Hello everyone, happy sunday.

I just finished readjusting my true duals exhaust due to a pos plastic bag getting trapped and melted onto the exhaust. I was having an issue with not being able to get my CL to work at all. I had the car down for about 18 months so I figured the sensors went bad. I ordered brand new Denso O2 sensors and installed them while I was messing with the exhaust. Ive had this issue ever since I got the car. I noticed the previous tune had the "Closed Loop Enable" maxed at 280, LTFT disabled, and STFT disabled, and MAF high RPM disable at 10,000 rpm. This makes it run in OL SD 24/7. After I installed the brand new O2 sensors, I reenabled LTFT/STFT, put "Closed Loop Enable" back to stock numbers. I figured this would put me in CL almost right away since I live in Florida and the engine temp was already at around 90. However, after starting it up I noticed the O2 sensors kept reading 440-450 mv and my CL error reads 0. I thought I might have plugged them in incorrectly, but I didnt. I have Speed Engineering long tubes so I had to use the O2 extensions and I noticed the driver side sheathing got too close to the header and melted it but the wires looked intact all the way around. I have attached both my tune and log. If anyone could help me or point me in the right direction I would greatly appreciate it.

[GHuggins]

450mv's is an open circuit. Make sure your heater fuse or an O2 fuse isn't blown especially if some of the wiring was melted.

[blindsquirrel]

~450mV is what the signal pins in the PCM read when there are no sensors connected (it's called 'bias voltage'). You need to do a bypass test. Disconnect the sensors, ID which pins in the harness side are supposed to be the signal high back to the PCM. Monitor O2 voltages in the scanner. Should be ~450mV with nothing plugged in. Briefly jumper signal high to ground and it should drop to less than 100mV. Then, briefly jumper signal high to voltage, it should rise to over 800mV.

Make sure to ID the wires/pins first! Check voltages with a meter to be sure you aren't going to be jumpering to what's really the heater +12v, for example.

[WS6_LOU]

Thanks for the info, blindsquirrel. I wont have time today but I will give it a shot tomorrow. I did notice that for some reason while datalogging, my MAF reads hz but reads 0 for mass airflow no matter what. I searched google for a while but couldnt run in to someone who had the same issue. I ran it in MAF only mode and it seemed to run normal so im not sure whats going on. What do yall think could cause that and have you heard of anything like that before?

[WS6_LOU]

Finally got a chance to crawl under the car. After identifying which wires where which (nightmare since they were all faded and discolored), I jumped the ground to the signal high with no change in voltage. I then jumped voltage to signal high and it made no change either. Kept reading between 440-450 mv. It seems weird to me that they would both stop working, all though I dont remember if they worked at all so for all I know the previous owner could have had an issue with the o2 sensors not reading and never told me. Are there any specific grounds or fuses that would make the o2 sensors stop reading or iss this sounding like a wiring issue? Because I really dont want to be chasing wires around.

[blindsquirrel]

screenshot.13-05-2023 16.57.45.png

The only fuse & chassis ground is for the heaters. The sensor part goes direct to the PCM, there aren't even any connectors inline in the harness. I'd find both ends of the 4 sensor wires and make sure they're going where they're supposed to.

[WS6_LOU]

screenshot.13-05-2023 16.57.45.png

The sensor part goes direct to the PCM, there aren't even any connectors inline in the harness.

Thats what really worries me. I know the heater works because the sensors are hot to the touch even though my car has been off for the past 2-3 days. But if there is an issue with the wiring, id have to test both signal high and low wires for continuity throughout the harness. And if it is a problem with the wiring harness, id have to take it out no matter what because you cant get to anything in there. And that is waaaaay more work than I want to do right now considering I just finished removing the old engine, rebuilding an lq9, and throwing it back in by myself in a one car garage. I know its not getting any signal at the plug so its gotta be between the plug and the main harness connector on the ecu. Shoot me.

[GHuggins]

If the ecm is easy to get to just check everything at it. Make sure it's a wiring issue and not an ecm problem. You can splice into and do the same to ground checks at it. Don't recommend the power ones just in case you grab the wrong wire. Also it's easy enough to check power feeds via fuse checks to the ecm, so won't hurt to check them.

[WS6_LOU]

The ecu is really easy to get to. It?s between the fire wall and passenger strut all the way at the top. What I plan on doing is finding what pin is the high and low signal and running a continuity test from the harness extensions to the ecu connector. I?m really REALLY bad with electrical stuff but I would think that test would tell me if power is getting to the connector. If it isn?t getting power to the connector then I know it?s a wiring issue (wouldn?t be a ground because as previously stated it?s a straight shot to the ecu), but if it is getting power then it must be a pin/ecu issue.

[GHuggins]

ECM's don't use just one power and one ground - at least not usually. You can still have a power supply or ground supply issue to that "part" of the ECM. This is why I said to check the fuses

Trust me Vengence Racing tuned one guys vette and couldn't get it to run right and then the customer looked me up. I asked him if he checked the fuses. He said Vengence surely would have checked that and known - right? His O2's weren't working either. I drove 2hrs to him. REPLACED the blown fuse from where he had a header melt his harness - of which he had already replaced the extensions and rerouted - and then tuned it. He was right there over my shoulder the whole time and couldn't believe that got overlooked. Also decided he was pretty happy with it and wasn't going to sale it anymore

Anyway - just saying keep it simple then go in depth and what you're saying is correct - as long as the ecm is functional it should show the voltage drop to near 0 when the signal is shorted to ground at the ecm connector. You can even have corrosion in the connector causing the issue or unfortunately in that location in the ecm itself...

[WS6_LOU]

What fuse did you end up replacing? I checked all mine and they were all good. Its possible I may have missed a ground when reinstalling the engine but I quadruple checked every forum for all the f body ls1 grounds and I made sure to install them all. It has to be an issue with the wire because no matter what I do I cannot get the ecu to read anything other than 440-450 mv verified through a log with the engine off. Tomorrow I will be locating the pins for the signal high and low wires on the ecu connector end of the harness run wires to test for continuity. Thats about the only thing I can think of that would have that effect.

[GHuggins]

It was a simple heater fuse. O2's never would get hot enough to start working due to their locations being way downstream with no cats.

Do what you have planned then - check connector at ecm and short signal to ground while watching voltage.

[blindsquirrel]

harness extensions

Would that be oxygen sensor harness extensions? Uh huh. Those are never pinned wrong.

[WS6_LOU]

At first I thought it was too, but I checked both harnesses and they seemed to be good. I made sure the wires were correctly placed too. I also tested the signal high and low at the harness plug so the harness extensions wouldn?t be a possibility. Like I said I know they are getting power because they are heated even with the engine off for a couple days. It just gets no signal to the ecu and constantly reads 440-450 mv. Today I will be unplugging the ecu to test the harness. I will report back with what I find.

[AnimateMe]

Something is screwed up if they are heated when the engine is off. The O2 heater circuit is powered by the pink wire, which should have 12v with key on and 0v key off.

[WS6_LOU]

So they are not suppose to be warm with the engine off? Because when I lifted my car up it had not been started in a couple days but the o2 sensors felt as hot as touching a glass of hot chocolate. Not scalding hot but pretty warm. Im wondering now if the harness extensions were wired incorrectly...but I didnt even think that could be a possibility.

[blindsquirrel]

screenshot.13-05-2023 16.57.45.png

Study closely. The fuse that powers the heaters says 'Hot with IGN'. If you have it powered some other way, it's wrong.

[gtstorey]

So they are not suppose to be warm with the engine off? Because when I lifted my car up it had not been started in a couple days but the o2 sensors felt as hot as touching a glass of hot chocolate. Not scalding hot but pretty warm. Im wondering now if the harness extensions were wired incorrectly...but I didnt even think that could be a possibility.

I bet that would drains a battery in a few days.

[blindsquirrel]

And if something that basic was done wrong, what else got done wrong?

[WS6_LOU]

So I let my car sit for 2 days while I waited for my torque arm and when I went to start it on day 3 after finishing the install, it was completely dead. Took 5 minutes of being connected to another car running to start up. This is on a brand new alternator and battery no older than 3 months. So what the hell gives? I didn?t wire anything. All I did was install the harness extensions I bought from the company that made my headers.