ALDL Mode 4 BCM Output Test commands on a VR Commodore

160 And 8192 Baud Aldl
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Joined: Mon Sep 09, 2019 9:59 pm

ALDL Mode 4 BCM Output Test commands on a VR Commodore

Postby picvrss » Tue Sep 10, 2019 11:21 pm


This is my first post, on my first forum, and firstly, I have to comment on the wealth of information and experience shared by contributors to pcmhacking - it's amazing stuff.

My profession and interest are in electronics, and this extends to designing and modifying electronic modules for my Commodore VR Series II SS, which I’ve owned for 24 years.

About 20 years ago, I replaced the factory Speed Alert dash module with a real-time ALDL ECM Monitor of my own design. It was based on a Hitachi 6303 microprocessor, and in addition to its primary function as a in-dash scan tool, it also retained the functionality of the original Speed Alert module.

Move on 20 years, and I replaced the ECM Monitor with a new PIC-based design, and added BCM Monitoring and Trip Computer/Fuel Consumption functions, which was easy to achieve.

This then led me to consider adding actuation of various BCM-controlled functions such as the Dome lamp, Indicators and Door Locks using ALDL Mode 4 Output Test commands to the BCM. Such commands have been the subject of several excellent posts on this forum, but these have been for VT - VZ models. Accepting that I might never get access to a Tech 1 from which I could sniff the required ALDL commands, I bought a Vident I-400-Holden scan tool, which was specified as being able to perform Actuator Tests with the VR BCM - in short, it can’t.

However, it does so with a VS BCM. As an example, to turn on the Dome lamp in a VS, the required Mode 4 command is:

$F1, $5D, $04, $00, $10, $00, $00, $40, $00, $00, $5E

I figured the only difference between the command structures for VR and VS should be only in the initial ID byte - $F1 for VS, and $BD for VR – and of course, in the final checksum, so I tried sending the following command to the VR BCM:

$BD, $5D, $04, $00, $10, $00, $00, $40, $00, $00, $92

There was no response from the BCM, nor was there to any Mode 4 command.

Would anyone out there know the command message structure of Mode 4 Output tests on a VR Low-level BCM?

Any advice would be very much appreciated.


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