Page 1 of 1
reading speed sensors
Posted: Mon Nov 02, 2009 5:33 pm
by MountainManJoe
Front Propshaft Speed Sensor - The transfer case shift control module converts the pulsating AC voltage from the front transfer case speed sensor to front propshaft speed, in RPM to be used for calculations, and to monitor the difference between the front and rear sensor speed. It is also used in the AUTO 4WD mode to determine the amount of slip and the percent of torque to apply to the front axle. The front propshaft speed can be displayed with a scan tool.
Rear Propshaft Speed Sensor - The transfer case shift control module converts the pulsating AC voltage from the rear transfer case speed sensor to a rear propshaft speed, in RPM to be used for calculations. The rear propshaft speed can be displayed with a scan tool.
Vehicle Speed Sensor - One of the 2 speed sensors on the rear output shaft is the vehicle speed sensor (VSS) input to the powertrain control module (PCM). The PCM sends this information to the transfer case shift control module via the Class 2 serial data bus.
Any OBD experts out there? What is the command to send to obtain data from these sensors? (I have a Scanguage)
Re: reading speed sensors
Posted: Sun May 02, 2010 9:20 pm
by MountainManJoe
I just found potential PID's for these sensors:
Transmission Input Speed: Mode $22 PID $1941
Transmission Output Speed: Mode $22 PID $1942
I'll test these soon and post my results.
Re: reading speed sensors
Posted: Mon May 03, 2010 5:05 am
by astrozam
All you could ever want to know about OBD11...
http://www.obd-codes.com/
Re: reading speed sensors
Posted: Mon May 03, 2010 8:14 am
by MountainManJoe
That's a good website astrozam, but it looks like it's just about trouble codes. This topic is about querying the PCM for vehicle information. They are called Mode 22, enhanced GM, or non-standard parameters. GM charges $50K for access to this kind of proprietary information, and you have to go into a non-disclosure agreement with them. Some people manage to reverse-engineer them though, so a few float around the internet.
Re: reading speed sensors
Posted: Mon May 03, 2010 8:22 am
by astrozam
I stand corrected
Re: reading speed sensors
Posted: Tue May 04, 2010 2:14 pm
by MountainManJoe
I'm going to start posting my findings in this topic:
http://www.astrosafarivans.org/bb2/view ... =10&t=5826
Re: reading speed sensors
Posted: Fri May 07, 2010 9:54 pm
by Lumpy
Hey Timeless!
How's your research going on VSS? Mine is bugging the heck out
of me for some generated RF interference.
Craig 'Lumpy' Lemke
www.n0eq.com
Re: reading speed sensors
Posted: Sat May 08, 2010 2:03 am
by MountainManJoe
Lumpy wrote:Hey Timeless!
How's your research going on VSS? Mine is bugging the heck out
of me for some generated RF interference.
Craig 'Lumpy' Lemke
http://www.n0eq.com
Hi Lumpy.
There are protocols for the transmission input and output speeds, and they are supported on my van. I haven't been able to decipher the data yet though. My reference material is very limited, so it's like stabbing in the dark.
Re: reading speed sensors
Posted: Sun May 09, 2010 8:34 pm
by MountainManJoe
One reference tool I'm using is this Wiki page:
http://en.wikipedia.org/wiki/OBD-II_PIDs
For the PID's which I've captured with my Scanguage 2 (SG), I'm getting 2 byte responses instead 1, and 3 byte responses where I should get 2 (such as 0x10 MAF). It's possible that the ECU appends some kind of control byte or CRC to the data, but which position? Also, I thought the SG handles error correction itself.