OBDII Data: Calculated LOAD Value

 Back in December we covered Absolute Load and it's relationship with Calculated Load. 

https://ggautobiz.blogspot.com/2025/12/obdii-data-absolute-load-value.html

This time we will take a look at how these data items and recording during a drive led to a diagnosis and repair for low power. No codes, no misfires but this 2015 Jeep Patriot just didn't feel strong on a hard acceleration. I've mentioned how the relationship between calculated and absolute load can help you spot a breathing problem. I took the scan tool on record along for a drive and was recording all data because I wanted to go through any that looked attention grabbing when I returned. I mention that because when you are recording ALL the data pids it can cause a slight discrepancy in the time line due to the time needed to exchange that much information. I did try a wot event. (wide open throttle) briefly and just looked for my peak of each of these at that time and pasted together for this article. 

The Calculated Load reached 100% which means the computer recognized the need for power but the Absolute Load only reached 68.6 which is struggling to meet it. Now this is basically the ability of the engine to pull in air and expel it (exhaust) so indicates either trouble getting enough air or an exhaust restriction. But we can see here the Relative Throttle is only 21.2, for some reason that throttle isn't opening enough to allow enough air for the event. 

 I had a plan based on that alone. Look at these spark plugs, which were badly worn. Look at this air filter, which needed replaced and inspect this throttle body which needed cleaning. Cleaned the throttle, replaced the air filter and replaced the spark plugs. The next drive I only recorded those data items so got it on one view. Calculated Load 100, Absolute Load 95.7 and Relative Throttle 77.3............ Ready to Rumba!

Thanks for reading!

Kenny@GGAuto.Repair

OBDII Data: Barometric Pressure

 The barometric pressure in my area was 30.18 so lets compare some cars. The 2009 Hyundai Elantra Barometric Pressure pid was in PSI rather than inHg so math, 14.5 PSI x 2.036 = 29.52 inHg. When you see about 14 or 15 on that pid you are seeing PSI. The Hyundai has an actual Baro sensor soldered into the printed circuit board of the PCM. We will call that 29.52 close enough. The Barometric pressure from the weather report is usually corrected to sea level so subtracting .3 would be the raw (what the car feels) pid. 29.88 inHg. A faulty Baro reading on the Elantra would cause a subtle shift in calculated load, and some related shifting concerns. 

   Lets take a look at the pid on the 2008 Chrysler 300C. The gold standard is met, 29.8 from the Chrysler Baro sensor, I believe it is also a part of the PCM on this model. 

Chryslers are big on logic, and rationality. When you turn the key on prior to start it will compare things, taking it all into account. For instance, since the engine is not yet running the MAP reading and Baro reading should match. It will monitor throttle position, map and baro once running to see that the readings make sense. It uses that Baro pid to calculate pressure ratio. If it sees something irrational it can go into limp mode, or disable the cylinder deactivation since it can't determine the load values. 

2000 Ford Taurus 3.0 DOHC: RED FLAG. 

The Ford is showing a Baro pid of 13.2 psi, or 26.87 inHg. Now the Ford doesn't have an actual Baro sensor. It calculates the Baro based on MAF sensor readings. Seeing the Baro off makes me suspicious of the MAF sensor. 

Interestingly enough the g/s of the MAF was 3.96 so slightly high but not alarmingly so. What seemed out of place is the long term fuel trim of 7%. Off into theoretical land, since the Baro pid was 26.87 perhaps the computer sees the higher altitude than actual and is using a fuel control strategy for "thin air". 

A quick wide-open-throttle gave me 104.4 g/s airflow before the rev limiter kicked in so lets clean that MAF and see what happens. It is not easy to safely reach that lower spool which would be the culprit but we'll give it a shot.

After cleaning i am idling at 3.43 g/s. Baro is now changed to 26.8. WOT is 110.79. Cleared the KAM and Baro went to 28. Time for the test drive. It may take awhile for the PCM to recalculate that Baro pid but it is headed in the right direction. 

TEST DRIVE: WOT load hit 95%. g/s airflow reached 127.35, LTFT is now 0, Baro is still 28 but it is just a slow learner. Major improvement.

Thanks for reading.

Kenny@GGAuto.Repair

 

1985-86 Audi 4000S Belt Adjustment