Smog Sensors Not Saving Info To ECU/PCM

[Raign00]

Hello all!

I am having a problem with my ECU not stroing the data from my smog sensors. When I drive and have the vehical on the data is there but when the smog tech turns of my truck and then turns it back on to perform the smog, the data disapears. The tech said something is not keeping the memory on the ecu powered which is why its not getting saved and not showing up when i go for a smog test. Please help, any info is greatly appreciated.

I have checked some fuses but not sure if im checking the right ones. Also smog tech said it could be also be a relay?

TY!

 

[Fless]

Would like to have some additional info to work with. Year, model, engine, mileage, etc. Also any recent work on the drivetrain?

What specific data items are you viewing from your smog sensors; which ones are "there" when the engine is running, but go away when it's not?

Is this a case where the scan tool is showing "not ready" for some of the emissions system tests? Or?

 

[Doubeleive]

Hello all!

I am having a problem with my ECU not stroing the data from my smog sensors. When I drive and have the vehical on the data is there but when the smog tech turns of my truck and then turns it back on to perform the smog, the data disapears. The tech said something is not keeping the memory on the ecu powered which is why its not getting saved and not showing up when i go for a smog test. Please help, any info is greatly appreciated.

I have checked some fuses but not sure if im checking the right ones. Also smog tech said it could be also be a relay?

TY!

does the radio/clock retain the correct time/station? or does it reset each time you cycle the key & open/close the drivers door?

 

[Raign00]

does the radio/clock retain the correct time/station? or does it reset each time you cycle the key & open/close the drivers door?

yes all setting like clock and radio stations are not lost. Also I have check that the battery is good and working properly. Only info that is NOT being stored is the smog sensor data.

 

[Raign00]

Would like to have some additional info to work with. Year, model, engine, mileage, etc. Also any recent work on the drivetrain?

What specific data items are you viewing from your smog sensors; which ones are "there" when the engine is running, but go away when it's not?

Is this a case where the scan tool is showing "not ready" for some of the emissions system tests? Or?

Ty for your reply:

2004 Yukon SLT 4x4 w 251000 miles. 4.8L
No recent work on the DT.

From what smog tech tells me and also shows me, the data is there when I pull in with my truck running, he then plugs in his lil code scanner/reader and shows me that 5 or so data collection points are satisfied on his reader. Then cycles the yukon and when it turns on all 5 or so are now not reading any data on the scanner/reader. I have done 3 driving cycles as well and same scenario when I return to retest at the smog shop.

TY for your help!

 

[Fless]

Is there some reason he can't document the status and readings while they're there?

 

[Doubeleive]

yes all setting like clock and radio stations are not lost. Also I have check that the battery is good and working properly. Only info that is NOT being stored is the smog sensor data.

I would get a meter and start checking every fuse, if any are blown then replace it.
I would suspect maybe a fuse that provides constant power to the ecm is blown.
some fuses are labeled externally for xx, but may also provide power to other things that are not listed in the book
only the service manual will show the other things a fuse may be providing data or power too.
check all the ones in the engine compartment and the ones on the drivers side dash panel and maybe look on the right side dash panel also.
all you have to do is take a meter, put in on continuity and touch the outer metal tabs on each fuse, you do not have to pull each fuse.

 

[Doubeleive]

Is there some reason he can't document the status and readings while they're there?

doing a smog test requires checking that the check engine light is functional which requires restarting the vehicle

 

[smwalker]

Looks like a 20 amp fuse in the underhood fuse box Labeled PCM B?

Not sure though this does not look like the standard GM diagram, not sure why its off a bit.
Do you have your own scanner you are watching the Monitors? I am wondering if the SMOG tech got a new scanner and is reading it correctly. No but it would not have "Monitors this key cycle " screen for a 2004.

 

[swathdiver]

Just a little bit longer and you guys won't ever have to deal with CARB and smog inspections ever again.

 

[Fless]

Just a little bit longer and you guys won't ever have to deal with CARB and smog inspections ever again.

That's all well and good, but we need to pass for the foreseeable future. Change takes time, especially when governing agencies are involved.

 

[swathdiver]

That's all well and good, but we need to pass for the foreseeable future. Change takes time, especially when governing agencies are involved.

These are permanent and cannot be undone without a super majority. In the early 1970s legislation was passed and the automakers followed suit immediately. Been the same since as they took over bumpers, seat belts, etc.

CARB and California are feebly attempting to fight back but they're going to lose as they only had power because it was ceded to them. That power has already been taken away. CARB is bankrupt and they're going down fighting to preserve their corrupt, power-hungry institution. They other night they banned certain 2025 vehicles forever and that's not going to stand either. Nor did their scheme to regulate brake dust.