Thread: Rpm Pid

Originally Posted by mohfa

i'm really confused about the difference between the RPM and PID :
do they have the same parameter . i mean are the RPM params same as those of PID

From SAE J1930, PID means "parameter identification". It's an arbitrary identifier (number) assigned to one piece of diagnostic data.

From SAE J1930, RPM means "revolutions per minute". Under OBD-II the engine speed in revolutions per minute is parameter (hex) 0x0C.

So can i use the RPM params in OBD-II to get the ECU diagnostics as i do with PIDs , and is ELM 327 compatible with these RPM params

You can read the Engine Speed in revolutions per minute by asking for the correct parameter identification (PID). But there is no such "thing" as an RPM -- the acronym stands for (engine) revolutions-per-minute, and it's one of the data items (PIDs) available over OBD-II.

OH GOOD , i' so sorry joeyoravec i didn't mean RPM but PRN , sorry again
so what do u think about the confusion between PRN params and those of PID .


Sorry again


many thanks

From SAE J2178-2, PRN means "parameter reference number". It's a a two-byte number that identifies a specific parameter by name, physical unit, size in bytes, and scaling. This concept is compatible with the definition of a PID. This standard describes:

1. A method to organize the identifiers into categories
2. A way to describe the transformation from binary data to scaled physical units
3. A reserved range so the numbers would be identical for any existing 1-byte OBD-II PIDs
4. A few specific PRNs as example

The automakers have obviously read this standard. Most of them implement an enhanced/extended diagnostic mode with 2-byte identifiers, but few actually assign enhanced PIDs this way. Overall I don't feel that this section of the standard is very relevant today, or worth reading. Opinions may vary.