# How to use ODB data to detect throttle related emission problem?

Based on OBD II Standard PIDs

PID(hex) 11 Throttle Position value from 0~100%

How could we use this data to predict if there is going to be a problem?

https://en.wikipedia.org/wiki/OBD-II_PIDs

• What data do you have? What symptoms do you have? What car do you have? vtc as this is just a link... Commented Mar 17, 2020 at 7:11
• I just wanna to create a general method to detect the relevant problems
– Sean
Commented Mar 17, 2020 at 10:06
• Welcome to Motor Vehicle Maintenance & Repair! Please take a moment to take The Tour as well as read through the Help Pages. Commented Mar 17, 2020 at 11:52

By using OBD to get some key data, I developed a method to detect "throttle" related emission problems.

=== Background ===

The engine of the vehicle goes into the idle state (engine speed > 0, vehicle speed = 0) when waiting for the traffic lights. If the engine does not obtain enough air because of a throttle related problem (but not worse enough to flameout), then ECU will control to inject less fuel to maintain an Air/Fuel rate. The engine speed will drop (a small or big variation).

=== Method ===

1. monitoring the "engine speed" —— to detect the abnormal variation
2. check the changing rate of the "throttle position" —— to check if the throttle is getting stuck somehow

S - engine speed

T - target idle RPM

e - variation tolerance of engine speed during the idle state

if | S - T | > e, then the idling engine speed is not stable

p - throttle position

t - time

R - the changing rate of the "throttle position"

R = ΔP/Δt

if | R_max - R_median | > e during a period of time,

then we could say that R is not stable, which means, he throttle is getting stuck somehow

=== Data collected from OBD ===

1. engine speed
2. vehicle speed
3. throttle position

=== welcome to post your thinking ===