How does the ABS system work?

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
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hsv08
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How does the ABS system work?

Post by hsv08 »

Got a customer who has converted a HSV avalanche from AWD auto to RWD manual

Now issue is, when loss of traction is acheived, the factory AWD ABS module would brake the rear wheels as soon as soon as the brake was touched ( this is due to the AWD ABS sytem stopping wheel slip under braking)

Now ive swapped out the PIM to a RWD one, and cut the 12v 4wd logic wire, so thats all good, PIM registers as a 2wd RWD now.
BUT
we still have warnings on the dash ( fault code is ABS module misconfiguration)

What i want to know is how and where does the ABS module send its configuration to the cluster?

Bearing in mind that utes dont even have ABS so how is the cluster still staying happy?

Customers got a rwd ute ABS module that i need to repin loom and plug to accept, but want to makesure that after ive done that ill get rid of the warnings and there wont be another module talking to the cluster saying its mis configured?
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Re: How does the ABS system work?

Post by pman92 »

The BCM polls every module once every 128ms (PCM twice, but everything else once).
When asked by the BCM each module will send off its data packet (EG. PCM packet will contain dash cluster values, SRS will contain airbag deployment and fault status).

Each type of ABS/TC will have a slightly different packet for whatever reason.

The dash cluster has to be programmed to tell it what ABS packet to expect to receive.

It also has to be programmed to tell it what SRS packet (how many airbags are fitted)
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Re: How does the ABS system work?

Post by hsv08 »

pman92 wrote:The BCM polls every module once every 128ms (PCM twice, but everything else once).
When asked by the BCM each module will send off its data packet (EG. PCM packet will contain dash cluster values, SRS will contain airbag deployment and fault status).

Each type of ABS/TC will have a slightly different packet for whatever reason.

The dash cluster has to be programmed to tell it what ABS packet to expect to receive.

It also has to be programmed to tell it what SRS packet (how many airbags are fitted)
Thanks for that.
From what I can put together, the AWD abs module is sending its packet via class 2 to the pcm and pim so the pim must be sending that back to the bcm by secondary UART then bcm forwarding to the IC

Where as the RWD abs module is sending it’s packet direct to the bcm by secondary UART then being forwarded to cluster.

But what I don’t understand is that you can swap any cluster in and out of any vehicle (vz for eg) in any form (trac control or ASM or no trac control etc) and won’t set a warning other than airbag configuration if it’s wrong

But the cluster has no where inside it to set the ABS type through either mdi or through body diagnostics.

So it must be getting its configuration setting from somewhere else?
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Re: How does the ABS system work?

Post by hsv08 »

On the bench, I can have a Vz cluster hooked up, Vz v6/6.0l pim on and a Vz bcm

I can go into the Pim and program that to be either no abs, abs, abs/tc or abs/asm

When programming no abs, the cluster won’t set a abs warning off. Set as anything else it will go off.

In a ls1 pim you cannot configure this.
Only awd or rwd (of which you can’t program anyway as it fails due to having to rewrite the entire os)

Which makes me think the ls1 pim is just a middleman for the ls1 awd abs and relies on the bcm to send the message to the cluster

So in other words I recon the V6 and 6.0 abs units units send to the pim, and the pim decides if it’s programmed to see the correct incoming data packet then sends straight to the cluster


And Ls1 awd abs unit is physically different but outputs a class 2 packet to the pim which sends to bcm then to cluster
And the rwd ls1 abs Sends straight to the Bcm then to cluster by UART ???
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Re: How does the ABS system work?

Post by oldn64 »

hsv08 wrote:On the bench, I can have a Vz cluster hooked up, Vz v6/6.0l pim on and a Vz bcm

I can go into the Pim and program that to be either no abs, abs, abs/tc or abs/asm

When programming no abs, the cluster won’t set a abs warning off. Set as anything else it will go off.

In a ls1 pim you cannot configure this.
Only awd or rwd (of which you can’t program anyway as it fails due to having to rewrite the entire os)

Which makes me think the ls1 pim is just a middleman for the ls1 awd abs and relies on the bcm to send the message to the cluster

So in other words I recon the V6 and 6.0 abs units units send to the pim, and the pim decides if it’s programmed to see the correct incoming data packet then sends straight to the cluster


And Ls1 awd abs unit is physically different but outputs a class 2 packet to the pim which sends to bcm then to cluster
And the rwd ls1 abs Sends straight to the Bcm then to cluster by UART ???
While i dont know and i had to read your post 3 time to get what you are trying to say I will place this into the equation for you. Holden produced a v6 AWD wagon. not a performance model or anything. I am confident that they would not have rewritten their whole software to accomodate ti and would still believe that the BCM is the one the communicates with the dash and hence the one that the ABS model also communicates with. The pim would not contain this data nor would it get involved.

I might be able to find out or at least find someone who worked on this model to ask the question if needed. Whether they will give me the information is a different matter.

cheers
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Re: How does the ABS system work?

Post by hsv08 »

Thanks for your reply. The V6 and 6.0 definitely does communicate with the PIM and decides if the message is valid or not ( can confirm this by removing the abs from the bench and programming pim to no abs and instrument cluster stays quite)

But from what I gather the bcm is only looking for either one data string that says the abs is not happy, or that it’s not the correct string for the type of abs set as per the pim
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Re: How does the ABS system work?

Post by hsv08 »

This is the awd gen 3 abs unit diagram which shows the only communication is to the pim and pcm via class 2
61B2A5B4-18BB-4AFC-9FCD-0B4E3AE0453A.jpeg
61B2A5B4-18BB-4AFC-9FCD-0B4E3AE0453A.jpeg (438.95 KiB) Viewed 3796 times
And the gen 3 rwd abs unit diagram that shows the only comms is straight to bcm via UART
63498B99-A666-4F79-AA47-73F876707BF7.jpeg
63498B99-A666-4F79-AA47-73F876707BF7.jpeg (480.36 KiB) Viewed 3796 times
So they are definitely communicating to different modules by different protocols between awd and rwd
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Re: How does the ABS system work?

Post by delcowizzid »

Might have to swap abs module and wire to the bcm like 6.0rwd .the 4wd would of sent it via pim for the yaw control (4 corner traction control) it had a special name I think I talked to you about on messenger .pim would of been sending data from abs to the ecu
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Re: How does the ABS system work?

Post by pman92 »

Sorry I assumed Abs was programmed like srs type in cluster.

The module's dont send there info to the bcm and the bcm sends it to the cluster, the BCM just sends a message to the module to tell it to broadcast it's message.
(The bcm is bus master, other modules will not speak unless spoken to to prevent data collisions).
EG. BCM says "ABS send your data", then the ABS sends it data, and any module on the data bus can see it and use as required. Chances are the BCM only checks for the ABS response so it can log a "no communication with ABS" DTC if required, but doesn't look at or care for any of the actual data.

As for your actual problem, if the AWD module doesn't talk ALDL (only class 2), and the RWD PIM is not expecting/programmed to pass on ABS messages (since rwd ABS talks ALDL directly), maybe the only option is to swap the ABS module out for the RWD one?
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