ALDL - Serial Data Port monitoring ?

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ALDL - Serial Data Port monitoring ?

Postby JohnDee68 » Fri Sep 25, 2020 8:45 pm

Hi, this might be a very straight forward issue to deal with by the guru's, so i am hoping i can get some guidance here please .

I want to ideally be able to note changes in a PCM's memory locations live at the time via the ALDL connection in my car.

I am not 100% sure where to start or what i really require, as something may already be freely available for me to do it that i am yet to know about.

What i have in mind is this. With my ALDL cable connected to the working PCM in my car, i would like some software that I can tell to scan or monitor a range of memory locations, so if any of those monitored locations change, it flags and displays that location as it changes.

My intent would then be, I can say monitor a range of address location at a time that monitors for example the Park lights, head lights, A/c switch, brake pedal switch, door lock switches, etc. Of course it will only monitor that of those which go through the PCM (i think even if via the BCM).

I guess what i am asking, is if there is software out there which either already does this or even something i can work on to get my end results?

appreciate thoughts and advise as always.

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Re: ALDL - Serial Data Port monitoring ?

Postby j_ds_au » Sat Sep 26, 2020 12:19 am

Maybe you can use TunerPro RT. You would need to edit an ADX file matching your ECU, so as to display the items you are interested in monitoring.

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Re: ALDL - Serial Data Port monitoring ?

Postby antus » Sat Sep 26, 2020 10:27 am

No there is nothing. Aldl is too slow to do this real time, and there is no software in the pcm for this. Closest thing is ram tracing with a moates ostrich emulator but for a flash pcm there is nowhere to plug it in and while not impossible it'd be quite a soldering job to wire it in place of the flash. and im not sure if it'd have ram visability though i suspect it might. most (all?) those sensors you mention dont go through the pcm, you'd be better building some kind of external hardware monitor and putting it on those circuits.
Have you read the FAQ? For lots of information and links to significant threads see here: viewtopic.php?f=7&t=1396

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Re: ALDL - Serial Data Port monitoring ?

Postby JohnDee68 » Sat Sep 26, 2020 4:59 pm

thanks antus and j_ds_au for the feedback and advice,

antus, i presumed that the PCM monitors or at least would know whats happened/happening to the vehicle, or am I far off track there?

I know there is things like last few minutes records on the PCM which can and sometimes is used in vehicle accidents by the police. I know that on some vehicles there can be such feedback via the OBD connections to show if there are things like dash switches operations on/off ect. So I just presumed it''l be the PCM that has knowledge of this somewhere within it at some time.

I just visulised this scenario, so it doesnt need to be instant i guess.
Sitting in the vehicle, connected up to the PCM via the OBD connector (ALDL) in my case.
run the monitoring search software for say a memory location (which has knowledge of dash switches) and press a switch for say whippers. Monitor the change in the software and if it repeats constantly on/off with each on/off of the switch, its a good chance that is the location in the memory of the PCM thats for that switch.

does that make sense or am i off track in my explanation.

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Re: ALDL - Serial Data Port monitoring ?

Postby pman92 » Sat Sep 26, 2020 8:17 pm

The PCM stands for Powertrain Control Module. Its purpose is engine and transmission related (powertrain).
Most or some of the things you have mentioned would include the BCM (body control module) in their circuit. Not necessarily controlled by the BCM, but the BCM may have an input to know what some of them things are doing.
Some of that data may be able to be logged from the BCM via ALDL, but it would be very slow and congest the ALDL bus.
Just as with the PCM, there is no software within the BCM that would trace its RAM locations either.

Some more modern vehicles may record some crash data when there is an SRS deployment. This certainly isn't the case for VX/VY commodores. I don't know for sure but I imagine the data stored would be stored in the SRS module (called SDM module in the GM world). That's the module that senses a collision and actually deploys airbags and pretensioners. The data would include a few basic things only. For example, vehicle speed, brake and accelerator pedal position, steering angle input. This data would be sent from the ECM/PCM to the SDM over a much higher speed data bus than ALDL, eg. a CAN network. The SDM may receive and record this data maybe once a second. It might record it for a couple of seconds, at most maybe 15 or 20 seconds worth.

So after a collision there may be half a dozen data points, for half a dozen data items, accounting for half a dozen seconds pre-collision. There's certainly no recording of where each dash switch was minutes prior to an accident
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Re: ALDL - Serial Data Port monitoring ?

Postby antus » Sat Sep 26, 2020 10:39 pm

you might also be missing a layer in your thinking. there is a data acquisition layer, referred to as logging, where certain data can be requested by type. It is read from ram, but you are not directly reading ram like you ask and it usually is updating quicker than you can keep up with. this is fine for purposes like logging, or a dashboard. in the delco computers you ask for a mode 1 frame and you get back particular data, pull certain things out from different offsets. you dont need to know where in ram it was stored. thats what the adx files are for when logging. in later obd2 systems you request pids, with one element of data being one pid. there are standard and proprietry pids, and if you request a standard sae pid from any obd2 vehicle you'll get the same piece of data back, regardless of the differing details of different hardware, software, ram location in different pcms.
Have you read the FAQ? For lots of information and links to significant threads see here: viewtopic.php?f=7&t=1396

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Re: ALDL - Serial Data Port monitoring ?

Postby JohnDee68 » Sat Sep 26, 2020 11:43 pm

thanks pman92 and antus,
you have both made the smoggy lenses i was apparently viewing things through, now a lot clearer.

antus, are you saying with the more newer vehicles they have finally got a more wider spread "standard" using pids which in my view should then be a lot easier to deal with data from the vehicles now than back in the early 2000's ?

thanks again everyone for the feedback. its been a very educational session.

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Re: ALDL - Serial Data Port monitoring ?

Postby antus » Sun Sep 27, 2020 12:42 pm

Yes I am SAE "Society of Automotive Engineers" standard J1979 https://en.wikipedia.org/wiki/OBD-II_PIDs
Have you read the FAQ? For lots of information and links to significant threads see here: viewtopic.php?f=7&t=1396

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Re: ALDL - Serial Data Port monitoring ?

Postby pman92 » Sun Sep 27, 2020 4:38 pm

Also important to remember in your case that SAE J1979 is one of the "OBD2" standards for the american market. There is others as well, such as J1962 which has the 16 pin "OBD2 Connector" and pinout. They were mandated in the USA as of 1996.
No vehicle sold in Australia, Europe or any part of Asia that I'm aware had to comply with them. It was basically a rule that said if you sell a new car here in america it must do this.
As of 2001 vehicles sold in Europe/EU had to comply with "EOBD" regulations. EOBD and OBD2 are essentially the same thing, it's europes version of it.
And since 2005 vehicles sold in Australia have to comply with ADR 79, which is again Australias version of essentially the same thing.
Japan also has OBD2 equivalent regulation.
Some other parts of the world don't even have regulation saying your car must be "OBD2 compliant", but since cars a global market every car built today is anyway.

So since your VY commodore was built somewhere between 2002-2004, long after the 1996 regulation in america, it was an Australian car built for the Australian market and is not OBD2 compliant. And the connector is not an OBD2 connector, even though it is physically the same size and shape and has some similar pinouts (eg. position of battery and earth pins).
ALDL is also not an OBD2 protocol. Most american market GM vehicles were using "Class 2" J1850 VPW by 1996, even if they also still had an ALDL data bus. ALDL was well and truely old technology by the time the VY commodore was sold.
VR-VY Holden BCM Simulator: LINK
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Re: ALDL - Serial Data Port monitoring ?

Postby JohnDee68 » Sun Sep 27, 2020 8:40 pm

Thank you again pman92 and antus,
all good info and informative.

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