Motor Age Technical Editor, Brandon Steckler is back again with some more diagnostic nuggets from the driver’s seat. This time reflecting on the value of the frequently under-utilized PIDs, Calculate Load and Absolute Load.
In this video Steckler reveals his regurgitated interpretation of the somewhat wordy SAE definition of each PID. Why?... So, techs will leverage them preliminarily in their driveability diagnostic approach.
Both the Calculated Load (CALC_LOAD or ENG_LOAD) and Absolute Load (ABS_LOAD) PIDs hold value in the diagnostic evaluation of the engine’s breathing capability. Meaning they both tell a similar story, but in a different language.
Calculated Load reflects how the engine is breathing during WOT at any point in time (regardless of elevation, engine temperature, air temperature, or rpm). This value represents available torque capacity, and it is compared to the engine’s maximum torque capacity (as in “100%”). The outcome is basically an expressed percentage value of maximum breathing capability.
Absolute Load is based on the engine’s swept volume. For instance, a 3.0L engine is said to be 100% volumetrically efficient if it moves 3.0L liters of air in one engine cycle. If we turbo charge that same engine, it can move far more air (because it is being force-fed under pressurized induction from the turbo charger). That engine (under full boost) may reflect 190% Absolute Load but, that is the most it can breathe (meaning, 100% Calculated Load).
Stick with Brandon in this video as he captures basic OBD2 global data from a scan tool from a normally functioning 2.3L turbocharged engine, and then when the turbo charger has been disabled. What do you expect to happen? Tune in to this episode of Mastering Diagnostics with Brandon Steckler and find out if your hypothesis is correct!
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