ELM327 & Class 2 Serial Data

@TJBaker57 Sorry for the wait but...

...Paydirt:

>AT SH CB E4 F1
OK

>1111
AA E5 C1 11 11 34 37

>1117
AA E5 C1 11 17 34 82

>1131
AA E5 C1 11 31 35 5F

>1137
AA E5 C1 11 37 35 EA

>2011
AA E5 C1 20 11 00 33 51

>2017
AA E5 C1 20 17 00 35 1A

>2031
AA E5 C1 20 31 00 34 32

>2037
AA E5 C1 20 37 00 34 37
 
OP
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TJBaker57

Well-Known Member
@TJBaker57 Sorry for the wait but...

...Paydirt:

>AT SH CB E4 F1
OK

>1111
AA E5 C1 11 11 34 37

>1117
AA E5 C1 11 17 34 82

>1131
AA E5 C1 11 31 35 5F

>1137
AA E5 C1 11 37 35 EA

>2011
AA E5 C1 20 11 00 33 51

>2017
AA E5 C1 20 17 00 35 1A

>2031
AA E5 C1 20 31 00 34 32

>2037
AA E5 C1 20 37 00 34 37
Curious that GM chose to return 2 bytes for the temp but only use the 2nd byte. I suppose that is also why they used a secondary ID of $20 for that parameter as the SAE designated temp ($10) only returns a single byte.

Have you got the equation for the temp? A common equation for temps is an offset of -40 then convert to Farenheit if desired. But that would put your 0x33 at just 51.8 F. That sounds a might cold for the date.
 
Curious that GM chose to return 2 bytes for the temp but only use the 2nd byte. I suppose that is also why they used a secondary ID of $20 for that parameter as the SAE designated temp ($10) only returns a single byte.

Have you got the equation for the temp? A common equation for temps is an offset of -40 then convert to Farenheit if desired. But that would put your 0x33 at just 51.8 F. That sounds a might cold for the date.
Crap, you know what? I don't think that's temperature. The numbers from last night match what I had from the 90+ degree day where I had driven around already. Last night the car was cold and the values are the same. Maybe temperature is hidden somewhere but I don't think that's it. I'm 99% we have the pressure, though.
 
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TJBaker57

Well-Known Member
Crap, you know what? I don't think that's temperature. The numbers from last night match what I had from the 90+ degree day where I had driven around already. Last night the car was cold and the values are the same. Maybe temperature is hidden somewhere but I don't think that's it. I'm 99% we have the pressure, though.

I'm curious what we have there then.

Try substituting $10 for $20 in your status request message. $10 is supposed to be temperature according to SAE J2178_4.
 
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TJBaker57

Well-Known Member
Crap, you know what? I don't think that's temperature. The numbers from last night match what I had from the 90+ degree day where I had driven around already. Last night the car was cold and the values are the same. Maybe temperature is hidden somewhere but I don't think that's it. I'm 99% we have the pressure, though.

Have you tried taking this reading in motion vs at rest? I am wondering what could this value be since it appears not to be a temperature. What else can a tire sensor report.... Battery level.... Maybe some rotational force??

Puzzled.
 
Have you tried taking this reading in motion vs at rest? I am wondering what could this value be since it appears not to be a temperature. What else can a tire sensor report.... Battery level.... Maybe some rotational force??

Puzzled.
Maybe its hardware ID? Doing some programming now on the application. I'll be going out in a little bit to test it. I'll try 10 instead of 20 then.
 
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TJBaker57

Well-Known Member
Maybe its hardware ID? Doing some programming now on the application. I'll be going out in a little bit to test it. I'll try 10 instead of 20 then.
But 2 of them are the same value... Seems unlikely. Is tire temperature something you know is being read by the sensors, like it shows elsewhere in the vehicle display?
 
But 2 of them are the same value... Seems unlikely. Is tire temperature something you know is being read by the sensors, like it shows elsewhere in the vehicle display?
I thought I could get it. Someone who had a van (Express) from 2008 said they found temps. I guess I was wrong.

But I do have this. I'm a dope and didn't take a picture of the actual GUI.
 

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TJBaker57

Well-Known Member
I thought I could get it. Someone who had a van (Express) from 2008 said they found temps. I guess I was wrong.

But I do have this. I'm a dope and didn't take a picture of the actual GUI.
Remember now, the last byte is only a checksum and has no value to you as data. Your data values from the picture are;

FL 0x34 = dec 52*4*.145038=30.167904 PSI

FR same as front left

lR 0x35 = dec 53*4*.145038=30.748056 PSI

RR same as left rear.
 
Remember now, the last byte is only a checksum and has no value to you as data. Your data values from the picture are;

FL 0x34 = dec 52*4*.145038=30.167904 PSI

FR same as front left

lR 0x35 = dec 53*4*.145038=30.748056 PSI

RR same as left rear.
Got it, thanks. I'll fix my formula now. It's a bit of a hassle going in and out of the house each time I update the program and load it to the RPi in the car. It's time consuming.
 
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TJBaker57

Well-Known Member
AT SH 89 48 F1 <enter>
10 <enter>
Recalling that bits 7, 6, and 5 of the first byte assign message priority with 0 = high and 7 = low it can be seen that the '89' in the command 'AT SH 89...' could also be A9, C9, or E9 for a lower priority, or 69 or 49, 29, or even 09 for a higher priority message, however I would avoid sending high priority messages. The other values of 19, 39, 59 and so on are not an option due to our requirement of bit 4 to be low as bit 4 denotes a 3 byte header form as GM uses. A high bit 4 would denote a single byte header form used by other manufacturers.
 
Recalling that bits 7, 6, and 5 of the first byte assign message priority with 0 = high and 7 = low it can be seen that the '89' in the command 'AT SH 89...' could also be A9, C9, or E9 for a lower priority, or 69 or 49, 29, or even 09 for a higher priority message, however I would avoid sending high priority messages. The other values of 19, 39, 59 and so on are not an option due to our requirement of bit 4 to be low as bit 4 denotes a 3 byte header form as GM uses. A high bit 4 would denote a single byte header form used by other manufacturers.
Gotcha. Just got in from trying that and trying the oil temp. Success. Thanks again
 

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