Python OBD encoding

I wanted to fetch some OBD data and tried it like described by this article
The article (using python 2.7) said:

The elm327 device returns values in HEX.

To read the value you just requested in Python type speed_hex = ser.readline().split(‘ ‘)

Convert the HEX to decimal by using: speed = float(int(‘0x’+speed_hex[3], 0 ))

But the answers I get from my OBD do not contain any whitespace furthermore they didn’t look like they made any sense at all.

 ['xd0MAr?rr>xd0x15r?rr>x981xf0n'] 

so I gave up on this approach and oved to Python 3 instead.

I then wrote a little script inspired by this SO post

However I changed it to pull a lot of data periodically and added a timestamp, all together is saved to a csv file – as the path implies I am working on Windows (10 to be precise), COM is correctly configured and the car is OBD compliant.

Now when I run my script it prints out what it read:

b'hxf4rSTOPPEDrr>' 

and then tells me

Traceback (most recent call last):
File "python3test.py", line 36, in <module> r.decode('utf-8')
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf4 in position 1:  
invalid continuation byte

I do understand that encoding certainly is an issue, but this string does not make much sense at all. even if I take a closer look at 0xf4 – it would only be 244 (dec) which is no where near sensible RPM data.

Why does it work in the other script then? It can’t be a Windows issue, can it?

Can anyone please help me understand whats going on in here?

Here is my code.

import serial
import time
import string
import io
import os
import sys
import datetime as dt


ser = serial.Serial("COM1")
ser.baudrate = 38400
ser.write(bytes('ATSP0rn', encoding = 'utf-8'))
ser.timeout = 1

ser.write(bytes('ATE0rn', encoding = 'utf-8'))
ser.timeout = 1

def millis_interval(start, end):
    '''start and end are datetime instances'''
    diff = end - start
    millis = diff.days * 24 * 60 * 60 * 1000
    millis += diff.seconds * 1000
    millis += diff.microseconds / 1000
    return millis

Testtime = str(dt.datetime.now()).split(' ')

PIDs = ["0C","0D","43","04","11","5C","05","10","46"]
response = []

''' open file and create header row'''
with open("C:/test/test_"+Testtime[0]+"_"+Testtime[1].replace(":","-")+".csv", "a") as myfile:
        myfile.write("Time,Timestep,RPM,Speed, AbsLoad, CalcLoad, ThrottlePos, CoolTemp, OilTemp, MAF, AmbAirTemp")


start = dt.datetime.now()    # need initial value
while 1:
    end = dt.datetime.now()
     
    myfile.write("n"+str(dt.datetime.now())+','+str(millis_interval(start,end))+)
    count = 0
    for s in PIDs:
        
        start = dt.datetime.now()
        ser.write(bytes(("01" + s) + 'rn', encoding = 'utf-8'))
        ser.timeout = 1
        ''' if answer not finished but new information sent OBD will stop writing and listen to UART *'''
        r = ser.read(999)
        while ">" not in r
             r = r + ser.read(999)
        print(r) # debug
        r.decode('utf-8')
        response[count] = r
        print(response[count]) #see what it looks like in utf-8
        
        myfile.write(str(','+response[count]))
        count +=1
ser.close()  

If it is of any interest: I am using an ELM327 compatible device via USB which seems to work flawlesly with the Scantool Software, my car is built 2000 and the ECU is a VW one.

• new information on the STOPPED info:
  https://www.scantool.net/forum/index.php?topic=10164.0