OBDII Data: Accelerator Position

 Because there is no throttle cable on a drive by wire system the computer needs to see what position you are placing the accelerator and it determines that by looking at the signal from the Accelerator Pedal Position sensor. Similar to the Throttle Position having redundant sensors, the Accelerator Pedal Position has two outputs that can be monitored in scan data as Accelerator Pedal Position D and Accelerator Pedal Position E. The system is set up that way so that if there is a sensor problem it will be noticed because the two outputs will no longer correlate. A mismatch here would set a P2138 and put the system into a limp in mode, limiting how much throttle can be given. Depending on application the two signals may vary in voltage output but they will always move together in sync as you press the pedal. 

Thanks for reading!

Kenny@GGAuto.Repair. 

OBDII Data: Throttle Position

 Electronic Throttle Bodies or throttle by wire systems have no accelerator cable and are responding to commands from the powertrain control module. Contained in the throttle body are two position sensors that relay the throttle position information back to the powertrain module so that it can "see" the response of the throttle to its commanded actions. Absolute Throttle Position is the data item for the primary sensor monitoring the butterfly valve angle. Absolute Throttle Position B is from a secondary sensor reporting the same information but on a different circuit to the powertrain module. This redundancy is for safety purposes and allows the powertrain module to cross-check and verify the information. Notice in the wiring diagram that the two sensors do share the same reference and return circuits. 

If the computer notices a discrepancy in the two signals it will set a fault code and go into a failsafe or limp-in mode that doesn't allow but a minimum of throttle. P2135 would be a result of that discrepancy. You can monitor and compare the two sensor outputs by looking at Absolute Throttle Position and Absolute Throttle Position B. They should correlate closely as the throttle moves. 

 On this particular application the signals are a mirror image of each other. 

Thanks for reading!

Kenny@GGAuto.Repair

 

OBDII Data: Absolute Load Value

 If you are using OBDII scan data you will notice a pid called Absolute Load Value. This is an indicator of the engine's current pumping response based on the demand and presented as a percentage. Think of this as a "Lung Capacity" test for your car. It shows how much air your engine is actually pulling in compared to the maximum amount it was designed to handle. For example, if this value is at 80% it means your engine is filling its cylinders 80% of the way with fresh air. It's a great way to see if your engine is breathing well or if there is a problem causing it to struggle for breath. Calculated Engine Load is what the computer is trying to do under current conditions, like giving 100% to sprint up that steep hill (wide open throttle for instance).  A comparison of the two data items can help determine if you have a breathing problem and what may be the cause. If you are looking for the cause of your car struggling up a hill or losing power on hard acceleration, and you see 100% Calculated Engine Load but a Absolute Load Value much lower then you have a problem with lung capacity. At a Calculated Load of 100% you want to see 85% or better Absolute Load. 70% to 80% is a red flag and anything less than 70% you definitely  have a restriction in intake or exhaust. Now there are other causes for power loss at wide open throttle, fuel delivery for instance, but a weak fuel delivery won't show up in your Load Values. You look for hints of that in fuel trims or by looking at air/fuel ratio sensor data during the problem. In Load Values if you see both Absolute and Calculated low at wide open throttle during the power loss you likely have a Mass Airflow sensor problem. We'll cover those topics later. 

"If your car has a turbocharger, don't be alarmed if your Absolute Load goes over 100%! A turbo literally force-feeds your engine, so it can actually breathe at 150% or even 200% capacity."

Thanks for reading!

Kenny@GGAuto.Repair