Pulling power to the computer will reset all the LT trims. So your initial readings reflected the fix of the TB gasket . For Trivia the PCM manages over 25 different LT trims, one for each BLM cell (engine operating conditions) 15 BLM cells for driving (speed > 0), 5 for idle conditions (TPS = 0 and speed = 0), the rest for deceleration and EVAP conditions.
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do I need to reset the ECU or clear codes when replacing O2 sensor?
- Thread starter sunliner
- Start date
What's BLM? (gotta remember, I'm quite the simpleton!)
I'd been plugging in the scanner every few days after driving just to see what it was doing. been trending down around 8-10% for a while but yesterday was the first time I'd seen it around zero.
I saw a table you linked to (i think it was you) that explained the codes in greater detail than I'd previously seen . If I read that right, one of the criteria for a lean code to set was that no evap codes are present...explains why I didn't get the 0171 until after I did the evap solenoid.
I'd been plugging in the scanner every few days after driving just to see what it was doing. been trending down around 8-10% for a while but yesterday was the first time I'd seen it around zero.
I saw a table you linked to (i think it was you) that explained the codes in greater detail than I'd previously seen . If I read that right, one of the criteria for a lean code to set was that no evap codes are present...explains why I didn't get the 0171 until after I did the evap solenoid.
bobdec said:Pulling power to the computer will reset all the LT trims. So your initial readings reflected the fix of the TB gasket . For Trivia the PCM manages over 25 different LT trims, one for each BLM cell (engine operating conditions) 15 BLM cells for driving (speed > 0), 5 for idle conditions (TPS = 0 and speed = 0), the rest for deceleration and EVAP conditions.
Sunliner - if you can remember where that table you mention above is, would greatly appreciate it as it may help with diagnosing a slight decrease in power that I'm having.
I had posted on this thread re: the P0171 prob a few weeks back; replaced both O2 sensors and cleaned the throttle body and it solved that issue. I've driven if for a bit since resetting the PCM per suggestion here and still find that it seems to be pulling for air at the low end of acceleration, or if I need it to downshift due to a slight incline. Responds well when I kick it out of overdrive, but the power profile still isn't quite right. I'm thinking that it's either some other mixture ratio issue or the cat has gone bad. No codes as of yet; am hoping to learn more about trim ratios and other sensor values before I just start replacing stuff.
I had posted on this thread re: the P0171 prob a few weeks back; replaced both O2 sensors and cleaned the throttle body and it solved that issue. I've driven if for a bit since resetting the PCM per suggestion here and still find that it seems to be pulling for air at the low end of acceleration, or if I need it to downshift due to a slight incline. Responds well when I kick it out of overdrive, but the power profile still isn't quite right. I'm thinking that it's either some other mixture ratio issue or the cat has gone bad. No codes as of yet; am hoping to learn more about trim ratios and other sensor values before I just start replacing stuff.
look around and find your vehicle here:
https://service.gm.com/gmspo/mode6/
https://service.gm.com/gmspo/mode6/
wbduval said:Sunliner - if you can remember where that table you mention above is, would greatly appreciate it as it may help with diagnosing a slight decrease in power that I'm having.
I had posted on this thread re: the P0171 prob a few weeks back; replaced both O2 sensors and cleaned the throttle body and it solved that issue. I've driven if for a bit since resetting the PCM per suggestion here and still find that it seems to be pulling for air at the low end of acceleration, or if I need it to downshift due to a slight incline. Responds well when I kick it out of overdrive, but the power profile still isn't quite right. I'm thinking that it's either some other mixture ratio issue or the cat has gone bad. No codes as of yet; am hoping to learn more about trim ratios and other sensor values before I just start replacing stuff.
Sorry answers are getting long, trying to keep a long topic short.. Fueling (keeping engine running correctly) is the critical job of the PCM, so it gets complex.
LT BLM = Block Learn Multiplier it's an older term you will see it mentioned, and it's still used by software. But the newer term used by scanners is called the Trim, BLM is a binary value between 0 and 255 where 128 equals a perfect burn. above 128 is lean and below 128 is rich. It's used directly to feed the fueling calculation. Trim is just a calculated the percentage of the BLM value + or - offset from 128. The + or - percentage is used as a display only that's easier to read on a scanner than the actual BLM binary value...
Now you asked about CELLS ... Take the trim value and multiply it by 25 iterations ... The BLM or Trim CELL is displayed on the scanner, do not confuse The trim cell with the trim value. There are 25 trim cells each for a different operational condition of the engine and each cell has a Trim value managed by the PCM. That way the PCM can remember and manage fueling for any of the 25 engine conditions differently. To accurately diagnose a rich or lean condition you need the Trim value AND the trim cell to do a complete job. EG: is the LT Trim bad at idle (trim cells 16 to 20) , or low load (trim cells 0-6), or heavy load (trim cells 9-14) , or entering WOT (trim cell 15) . Worse at idle no load points to vacuum leaks, worse at loads points to fueling problems..not always accurate but usually is..
LT BLM = Block Learn Multiplier it's an older term you will see it mentioned, and it's still used by software. But the newer term used by scanners is called the Trim, BLM is a binary value between 0 and 255 where 128 equals a perfect burn. above 128 is lean and below 128 is rich. It's used directly to feed the fueling calculation. Trim is just a calculated the percentage of the BLM value + or - offset from 128. The + or - percentage is used as a display only that's easier to read on a scanner than the actual BLM binary value...
Now you asked about CELLS ... Take the trim value and multiply it by 25 iterations ... The BLM or Trim CELL is displayed on the scanner, do not confuse The trim cell with the trim value. There are 25 trim cells each for a different operational condition of the engine and each cell has a Trim value managed by the PCM. That way the PCM can remember and manage fueling for any of the 25 engine conditions differently. To accurately diagnose a rich or lean condition you need the Trim value AND the trim cell to do a complete job. EG: is the LT Trim bad at idle (trim cells 16 to 20) , or low load (trim cells 0-6), or heavy load (trim cells 9-14) , or entering WOT (trim cell 15) . Worse at idle no load points to vacuum leaks, worse at loads points to fueling problems..not always accurate but usually is..