ODB2 Throttle Actuator vs Throttle Position

Hello,

Trying to sort out the throttle gauge feature. My OBD2 (Kiwi 3) shows options to monitor Throttle Actuator% (ID 4C) and Throttle Position% (ID 11).
The attached image file contains an output scan.
Attachment 62974

ID 11 reads 11.76%
ID 4C reads 1.96%
Vehicle is at idle (694.75 rpm).

Any thoughts on the following:
1) Why is ID 11 reading 11.76% with vehicle at idle and no throttle is applied by the driver?
2) ID 4C @ 1.96%, same here.
3) Presumably I should use ID 4C instead of 11 to represent throttle position in my case?
4) What does Absolute Engine Load (ID 43) represent?

1) The PID 11 throttle position is defined by SAE as an absolute position, typically relative to a 0-5 volt range. This will vary by vehicle, but it's common for closed throttle position to read around 0.5 volts and the WOT around 4.5 volts, which causes this PID to report something like 10% - 90%. It's very rare to see a vehicle that reports a full 0% - 100% here, and it's possibly wrong for it to do so according to the specification. This reading should be coming from the Throttle Position Sensor that's located in the engine's throttle body; it is not a sensor on the throttle pedal itself.

2) PID 4C is the commanded throttle actuator position for a throttle-by-wire engine, and should be 0% - 100%. The 1.96% percent you're seeing at idle is most likely due to the engine computer adding that to maintain idle, respond to some load, etc.

3) This is tricky because neither is really perfect for seeing the driver's throttle pedal position on these newer cars, and it can vary by vehicle. On some cars, they work out pretty well for seeing what the driver is doing, but on others they get a bit noisy/inconsistent. SAE also defined several parameters for reading the actual throttle pedal position, but many vehicles don't offer those particular SAE PIDs, so that's not of much help.

When you look at PID 11 or PID 4C, that relates to the throttle plate position, which is really under the computer's control on most throttle-by-wire cars. It's useful for engine tuning, but may leave something to be desired when you want to see the driver's inputs at a track. The engine computer may add some percentage at idle or whenever it sees increased load, and vehicles that operate using torque based control will take further control over this. It also may not always go to 100% when you're at full throttle, due to traction control, if the computer thinks you'll make more power at that RPM that way, etc. Right now, we're essentially limited to SAE parameters in this app, but are working on offering some additional options that could help here (no ETA just yet)...

4) PID 43 can be a much more lengthy explanation, but essentially it should start at 0% and read up to about 95% for an NA engine, or up to about 400% for a boosted engine. It should be linear in relation to engine torque, and the peak value should be your volumetric efficiency at WOT. The technical details for this and other PIDs are in SAE J1979, which gives this formula: LOAD_ABS = [air mass (g / intake stroke)] / [1.184 (g / liter) * cylinder displacement (liters / intake stroke)]


By the way, our next TrackAddict update should boost your OBD sampling rate a bit when logging a bunch of channels. I'm hoping to have that released in the next week or so...

Thank you for the detailed explanation and certainly clears up my understanding.
Look forward to the next TrackAddict update.