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Old 28th August 2012, 11:32   #1
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Default OBD2 Parameter IDs (PIDs) and what they mean?

I'm using the Torque app to monitor the sensor readings and most of the PIDs are straight enough for my understanding but there are some which i don't. What does the following PID means? All these provide readings.

Absolute Throttle Position
Relative Throttle Position

Accelerator Pedal Position D
Accelerator Pedal Position E

Engine Load
Engine Load (Absolute)

Fuel Pressure
Fuel Rail Pressure

Voltage (Control Module)
Voltage (OBD Adapter)
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Old 28th August 2012, 16:41   #2
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Default Re: Torque OBD App - What the PID means?

I remember reading that sometimes the app will show parameters listed even if your car doesn't have those sensors.

Best place to get answers would be the Torque forums (but they seem to be down today).

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Old 28th August 2012, 17:01   #3
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by Sankar View Post
I'm using the Torque app to monitor the sensor readings and most of the PIDs are straight enough for my understanding but there are some which i don't. What does the following PID means? All these provide readings.

Absolute Throttle Position
Relative Throttle Position

Accelerator Pedal Position D
Accelerator Pedal Position E

Engine Load
Engine Load (Absolute)

Fuel Pressure
Fuel Rail Pressure

Voltage (Control Module)
Voltage (OBD Adapter)
Have given below a brief description of each parameter that you have asked - it should be sufficient to understand the various terms:

Absolute Throttle Position – Actual position of the throttle
Relative Throttle Position – Amount of throttle opening

Accelerator Pedal Position D – The minimum opening usually about 5% above minimum.
Accelerator Pedal Position E – Similarly, the maximum position usually about 5% below maximum.

Engine Load – Engine load being used
Engine Load (Absolute) – Maximum engine load

Fuel Pressure – pressure given by the fuel pump
Fuel Rail Pressure – pressure within the fuel rail and which is given into the injectors.

Voltage (Control Module) – the voltage of the battery in the car in which the ECM is fixed.

Voltage (OBD Adapter) – the voltage in the Pin of the OBD (usually no: 16) that is connected to the car’s battery – this would also be the voltage of the battery in the car.
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Old 28th August 2012, 21:06   #4
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by VeyronSuperSprt View Post
Engine Load – Engine load being used
Engine Load (Absolute) – Maximum engine load
Hi VeyronSUpersprt, how is the engine load calculated. In some software's, they require us to input vehicle load, engine capacity and some other data to get accurate values. I'd like to know more about it.

Quote:
Fuel Rail Pressure – pressure within the fuel rail and which is given into the injectors.
I think most petrol vehicles don't have this, and but Common Rail engines have.
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Old 28th August 2012, 21:52   #5
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by dhanushs View Post
Hi VeyronSUpersprt, how is the engine load calculated. In some software's, they require us to input vehicle load, engine capacity and some other data to get accurate values. I'd like to know more about it.


I think most petrol vehicles don't have this, and but Common Rail engines have.
I am using torque pro too. During the first run the app asks to create vehicle profile like engine capacity, max rpm on the dial, fuel type, fuel tank capacity etc etc.
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Old 28th August 2012, 22:12   #6
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Default Re: Torque OBD App - What the PID means?

Sankar,


Did some Googling for you:

OBD-II PIDs - Wikipedia, the free encyclopedia
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Old 29th August 2012, 09:11   #7
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by dhanushs View Post
Hi VeyronSUpersprt, how is the engine load calculated. In some software's, they require us to input vehicle load, engine capacity and some other data to get accurate values. I'd like to know more about it.
Hi dhanushs, The easiest way to calculate engine load would be as a percentage of manifold vacuum as it is directly proportional to manifold vacuum. Manifold Absolute Pressure is the pressure delivered to the combustion chamber and manifold vacuum is the remaining pressure in the intake manifold. The Intake Manifold Pressure would show you the engine load also.

Very simply put, the engine load formula is a derivative of Fuel Intake / Rated Fuel Intake X 100 which is again derived from the original formula of Actual Fuel Rate / Maximum Fuel Rate X 100.

Quote:
Originally Posted by dhanushs View Post
I think most petrol vehicles don't have this, and but Common Rail engines have.
MPFI Petrol engines have injectors connected to fuel rails. It is the earlier single point injectors that were connected to the throttle body.
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Old 29th August 2012, 09:36   #8
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by VeyronSuperSprt View Post
Have given below a brief description of each parameter that you have asked - it should be sufficient to understand the various terms:

Absolute Throttle Position – Actual position of the throttle
Relative Throttle Position – Amount of throttle opening
I'm confused here because there is another PID which gives the value of the Throttle opening at the TB. So there are three PIDs for throttle out of which one i understood is the opening at TB, thats what i was confused about.

Quote:
Accelerator Pedal Position D – The minimum opening usually about 5% above minimum.
Accelerator Pedal Position E – Similarly, the maximum position usually about 5% below maximum.
Failsafe?

[quote[Engine Load – Engine load being used
Engine Load (Absolute) – Maximum engine load[/quote]
What is maximum engine load?

Quote:
Fuel Pressure – pressure given by the fuel pump
Fuel Rail Pressure – pressure within the fuel rail and which is given into the injectors.
Thanks!

Quote:
Voltage (Control Module) – the voltage of the battery in the car in which the ECM is fixed.

Voltage (OBD Adapter) – the voltage in the Pin of the OBD (usually no: 16) that is connected to the car’s battery – this would also be the voltage of the battery in the car.
Thanks!

Quote:
Originally Posted by VeyronSuperSprt View Post
The easiest way to calculate engine load would be as a percentage of manifold vacuum as it is directly proportional to manifold vacuum. Manifold Absolute Pressure is the pressure delivered to the combustion chamber and manifold vacuum is the remaining pressure in the intake manifold. The Intake Manifold Pressure would show you the engine load also.

Very simply put, the engine load formula is a derivative of Fuel Intake / Rated Fuel Intake X 100 which is again derived from the original formula of Actual Fuel Rate / Maximum Fuel Rate X 100.
Apart from that doesn't it also take into account the RPM, Gear, Timing, Road speed to calculate engine load?

Quote:
Originally Posted by theMAG View Post
Sankar,


Did some Googling for you:

OBD-II PIDs - Wikipedia, the free encyclopedia
Mag, I found it on Wiki, but it doesn't explain what Absolute & Relative throttle position or Engine load & Absolute engine load etc.


Quote:
Originally Posted by adityasiera View Post
I am using torque pro too.
Does logging work for you? I've been trying to tweet the log from within the app and it doesn't seem to do it. Neither to facebook.
Not sure if its a data connection issue.

Last edited by Sankar : 29th August 2012 at 09:38.
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Old 29th August 2012, 12:03   #9
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Default Re: Torque OBD App - What the PID means?

Found out that Absolute throttle position value in percentage matched closely with the Manifold throttle position. So that confusion is over.

At WOT
OBD2 Parameter IDs (PIDs) and what they mean?-screenshot_20120830_1134.png

Foot off the pedal
OBD2 Parameter IDs (PIDs) and what they mean?-screenshot_20120830_1135.png
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Old 29th August 2012, 12:18   #10
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by Sankar View Post
What is maximum engine load?
I guess it should show the max value in that specific run.

Quote:
Apart from that doesn't it also take into account the RPM, Gear, Timing, Road speed to calculate engine load?
Not really, I guess. Cos, at any speed, any gear, any rpm, engine load can be varied, where as, manifold vacuum is directly proportional to engine load at all times.

Quote:
Does logging work for you? I've been trying to tweet the log from within the app and it doesn't seem to do it. Neither to facebook.
Not sure if its a data connection issue.
It didn't work for me in the free app. Also the free app sucks, the refresh rate is damn too slow and inconsistent.

You get a full unlocked torque app online, but again you cant go online through that. Only option to go online in torque is through the paid version.
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Old 29th August 2012, 12:31   #11
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by Sankar View Post


Engine Load (Absolute) – Maximum engine load
What is maximum engine load?
I don't have much idea about what is engine load. However My Blue tooth OBD2 reader shows 100% engine load when ever I lug my engine,ie driving below 1500 rpm on Cruze. Engine load becomes 0% while driving downhill. While going uphill, engine load shows a higher reading. I use symbian applications, OBDscope and OBD autodoctor.

Last edited by anb : 29th August 2012 at 12:33.
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Old 29th August 2012, 14:45   #12
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by dhanushs View Post
Not really, I guess. Cos, at any speed, any gear, any rpm, engine load can be varied, where as, manifold vacuum is directly proportional to engine load at all times.
I think it should take the other parameters too to calculate the engine load. Otherwise wouldn't the calculated load decrease as soon as the throttle opens and the vacuum decreases? What happens when the vehicle is pulling a heavy load, the throttle at WOT?

How's the load calculated in case of Diesels turbo Diesels?

Quote:
It didn't work for me in the free app. Also the free app sucks, the refresh rate is damn too slow and inconsistent.

You get a full unlocked torque app online, but again you cant go online through that. Only option to go online in torque is through the paid version.
The refresh rate depends on the OBD scanner used, some expensive scanners seems to have high refresh rate according to their website.

I bought the paid app an year ago and now runs the latest update. Logging isn't working, maybe i'm missing something. Me previous car wasn't OBD compliant but was using it in the i10 occasionally.

Quote:
Originally Posted by anb View Post
I don't have much idea about what is engine load. However My Blue tooth OBD2 reader shows 100% engine load when ever I lug my engine,ie driving below 1500 rpm on Cruze. Engine load becomes 0% while driving downhill. While going uphill, engine load shows a higher reading. I use symbian applications, OBDscope and OBD autodoctor.
Yes lugging will increase the engine load.

PS: Cruze doesn't have manifold vacuum, so how is engine load calculated here?
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Old 29th August 2012, 19:57   #13
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by Sankar View Post
Otherwise wouldn't the calculated load decrease as soon as the throttle opens and the vacuum decreases?
Decrease in vacuum indicates increase in load so as the throttle opens and vacuum decreases it indicates increased engine load.

Quote:
Originally Posted by Sankar View Post
What happens when the vehicle is pulling a heavy load, the throttle at WOT?
WOT would, as replied above, show the max engine load.


Quote:
Originally Posted by Sankar View Post
How's the load calculated in case of Diesels turbo Diesels?
Air flow is used for the calculation instead of manifold vacuum. Current airflow as a percentage of peak air flow would indicate the engine load at that given point.


Quote:
Originally Posted by Sankar View Post
PS: Cruze doesn't have manifold vacuum, so how is engine load calculated here?
On the basis of air flow as indicated above.

Last edited by VeyronSuperSprt : 29th August 2012 at 20:17.
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Old 30th August 2012, 08:13   #14
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by Sankar View Post
I think it should take the other parameters too to calculate the engine load. Otherwise wouldn't the calculated load decrease as soon as the throttle opens and the vacuum decreases? What happens when the vehicle is pulling a heavy load, the throttle at WOT?

How's the load calculated in case of Diesels turbo Diesels?

PS: Cruze doesn't have manifold vacuum, so how is engine load calculated here?
I guess this answers my question regarding Load and Absolute Load.

Calculated LOAD Value (PID 04)

The OBD regulations previously defined CLV as:
(current airflow / peak airflow @sea level) * (BARO @ sea level / BARO) * 100%
Various manufacturers have implemented this calculation in a variety of ways. The following definition, although a little more restrictive,
will standardise and improve the accuracy the calculation.
LOAD_PCT = [current airflow] / [(peak airflow at WOT@STP as a function of rpm) * (BARO/29.92) * SQRT(298/(AAT+273))]
— Where: STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg BARO, SQRT = square root,
— WOT = wide open throttle, AAT = Ambient Air Temperature and is in °C
Characteristics of LOAD_PCT are:
— Reaches 1.0 at WOT at any altitude, temperature or rpm for both naturally aspirated and boosted engines.
— Indicates percent of peak available torque.
— Linearly correlated with engine vacuum
— Often used to schedule power enrichment.
— Compression ignition engines (diesels) shall support this PID using fuel flow in place of airflow for the above calculations.
NOTE Both spark ignition and compression ignition engines shall support PID $04. See PID $43 for an additional definition
of engine LOAD.
05 Engine Coolant Temperature A –40 °C +215 °C 1 °C with
–40 °C offset
ECT: xxx °C (xxx °F)
ECT shall display engine coolant temperature derived from an engine coolant temperature sensor or a cylinder head temperature
sensor. Many diesels do not use either sensor and may substitute Engine Oil Temperature instead.

Absolute Load Value (PID 43)

The absolute load value has some different characteristics than the LOAD_PCT defined in PID 04 This definition, although restrictive,
will standardise the calculation. LOAD_ABS is the normalised value of air mass per intake stroke displayed as a percent.
LOAD_ABS = [air mass (g / intake stroke)] / [1.184 (g / intake stroke) * cylinder displacement in litres]
Derivation:
— air mass (g / intake stroke) = [total engine air mass (g/sec)] / [rpm (revs/min)* (1 min / 60 sec) * (1/2 # of
cylinders (strokes / rev)],
— LOAD_ABS = [air mass (g)/intake stroke] / [maximum air mass (g)/intake stroke at WOT@STP at 100% volumetric efficiency]
* 100%.
Where:
— STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg (101.3 kPa) BARO, WOT = wide open throttle.
The quantity (maximum air mass (g)/intake stroke at WOT@STP at 100% volumetric efficiency) is a constant for a given cylinder swept
volume. The constant is 1.184 (g/litre 3) * cylinder displacement (litre 3/intake stroke) based on air density
at STP.
Characteristics of LOAD_ABS are:
— Ranges from 0 to approximately 0.95 for naturally aspirated engines, 0 – 4 for boosted engines,
— Linearly correlated with engine indicated and brake torque,
— Often used to schedule spark and EGR rates,
— Peak value of LOAD_ABS correlates with volumetric efficiency at WOT.,
— Indicates the pumping efficiency of the engine for diagnostic purposes.
Spark ignition engine are required to support PID $43. Compression ignition (diesel) engines are not required to support this PID.
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Old 30th August 2012, 12:37   #15
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Default Re: Torque OBD App - What the PID means?

Quote:
Originally Posted by Sankar View Post
I guess this answers my question regarding Load and Absolute Load.
There are many definitions available and the debate still continues as to which would be right. This looks similar to the open source definitions of Source Forge.

On another note, this level of detail is not required for home use of OBD scanners. Heck, even some manufacturers (not naming them) don't go to this level of detail when they do their calculations and which is why you find a difference between their stated specs and reality. The more accurate ones are the readings given at the time of homologation by bodies like ARAI etc. For home use OBD scanners it's best not to get into this level of detail.

Cheers!

Last edited by Rehaan : 30th August 2012 at 13:25. Reason: Fixing quote. Slash was wrong way.
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