Volvo B12B J1587/J1708

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flaurits
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Volvo B12B J1587/J1708

Post by flaurits »

Hello. I have this Volvo B12B 2003 with missing messages in the instrument cluster.
It has errors for Datalink J1587 comm. datalink missing message. Brake Pressure Circuit #1 and #2, engine oil temp. Component failure.

I tried decoding to see if i had comm. problems on the J1587 protocol.

I can communicate with instrument using J1939 but not J1587. I can see messages on J1587 regarding MID234 wich is Cluster #2 when looking in the SAE's. But not MID 140 Cluster #1. Looking at wiring diagrams i can see the cluster is divided in two.

Can someone see something from this file that i dont?

Best regards LEØ
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Steve Smith
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Re: Volvo B12B J1587/J1708

Post by Steve Smith »

Hello and thank you for the post, sorry for the late reply.

Looking at the decoded data and using the search function I too cannot see MID 140

MID 140 is referred to as Instrument Cluster here https://www.simmasoftware.com/wp-conten ... uction.pdf
1
1
Looking at the protocol for J1587, your decoded data is correct when we search for MID 234 and follows the protocol rules

i.e., MID 234, PID 254 (Variable length data) followed by PID/Data 127, 3, 212, 112, 0 and a Check sum of 82
2
2
Given the Pico decoder is functioning, the physical layer must be intact and communication is ongoing

One possible explanation could be a very slow poling of MID 140 but I doubt this very much given you have 13 buffers at 200 ms (each buffer) = 2.6 seconds of data

We could try to slow the capture rate down to 200 ms/div and start capturing from the point of Bus Wake up, we may momentarily capture MID 140 before it then goes offline

When trying to communicate via J1587, does the scan tool make its presence known on the Bus?

You mentioned the instrument cluster is divided into two, are both halves connected to the J1587 bus?

If this is the case, we have to conclude cluster 1 is offline for either power/ground error or cluster failure

I hope this helps, take care…..Steve

ben.martins
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Re: Volvo B12B J1587/J1708

Post by ben.martins »

Hello LEØ,

Thanks Steve for jumping in here, I too cannot find MID 140 for the Instrument Cluster.

Following on from the decoding topic here - https://www.picoauto.com/support/topic22640.html we can see the data being decoded into the MID and PID data. Remember due to the UART decoder we cannot rely on the Checksum being correct.

Quick question, when you were capturing this data was the scan tool still connected? The only reason I ask is that the PID found by Steve below PID 254 following MID 234, is a data escape PID with the first byte following this the MID for the desired receiving device being 127. This MID is defined in the J1708 document but not listed in the documentation I have.

Picking the PID for engine oil temperature this should be PID 175. In the above link we know that PID's between 128 and 191 should all have 2 bytes -
PIDs add a little more confusion due to the different lengths they can have depending on the parameter they represent. PIDs 0 to 127 and PIDs 256 to 383 use a single data byte to represent the value. For PIDs 128 to 191 and PIDs 384 to 447, two data bytes are used to represent the value. For the above example we have a PID of 190 which following the above conditions mean the next 2 bytes make up our data. PID 100 though falls in the first category which means there is only 1 data byte. More on this later.
Using this information we can start to look for 175 as Steve has done with MID140 using the filter option. I've done the same for 175 and received 3 hits.
J1587 bytes.png
Sadly though if we work out the byte position 175 is in the data section each time. It therefore makes sense that you are missing data rather than have an issue with the network. It would be worth seeing how those components you are missing data for are wired in, as this might give some direction. Check for common power supplies, shared grounds etc.

Hope this helps.

Kind regards

Ben

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flaurits
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Re: Volvo B12B J1587/J1708

Post by flaurits »

Hello Again.

First of thank you for both of your replys, Steve And Ben. I am still new to decoding, and Pid an Mid :D
But its really cool to see how this can be incorporated. Lots of time its really hard to get wiring diagrams for these trucks and busses.

When trying to communicate via J1587, does the scan tool make its presence known on the Bus?
-I did not check that, but i defently could not talk the module with the scantool.

Quick question, when you were capturing this data was the scan tool still connected?
-It could have been. I do not remember anymore. (lots of busses and vans through the shop since) It does tough sit outside with a errorcode of a bad injector Nr.4.

Check for common power supplies, shared grounds etc
I will regarding the Missing info, i also have a air suspension controller which only will air up when restarting the entire bus with full air pressure (suspecting a bad pressure sensor, low air pressure settings/leaks or ECU)

Best regards
LEØ, Denmark

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