reading speed sensors

[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)

[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.

[astrozam]

All you could ever want to know about OBD11...http://www.obd-codes.com/

[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.

[astrozam]

I stand corrected

[MountainManJoe]

I'm going to start posting my findings in this topic:
http://www.astrosafarivans.org/bb2/view ... =10&t=5826

[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

[MountainManJoe]

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.

[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.