ALDL resistive control and PWM control classes

[Daniel Burk]

I got it from a report written by Dr. Bradley Smith, dated January 13, 1986
titled: "Assembly Line Data Link Information - for 1982 - 1986 GM Vehicles".

It was written for and published by the GM CAMS (Computerized Automotive
Maintenance System).  This group was (I surmise) swallowed up into Delco back
in the late 80's.

 Most of the report is considered by GM to be unclassified; At least the part
detailing the data stream is, anyway.

After reviewing the report excerpt, I found that what I wrote was in error.

Here's the excerpt from the report, page 5, that details the various modes.
Essentially, there existed three distinct classes of ALDL equipped vehicles.
Here's the excerpt:

Varying modes on Vehicles:
    There are three classes of vehicles that have been produced by GM since
1982.  The first set of vehicles are those whose data streams are controlled
by placing a resistive value fron pin B to pin A of the ALDL connector. These
vehicles, called Resistive Control (RC) vehicles, represent the largest
portion of GM vehicles produced to date [1986 - drb]. These vehicles have the
following modes:
    Normal Mode     (R >=20K)
    ALDL Mode        (R==10K)
    Backup Mode     (R==3.9K)
    Field Service      (R<=500)
The Latter mode is also called shorted mode.  These modes instruct the ECM
about what functions to perform and what data to ship.

The second class of vehicles are those that are controlled by shorting pin A
to pin B.  This class of vehicles is controlled by the amount of time pin B
is shorted to pin A and is called Pulse Width Modulated (PWM) vehicles.  To
control the modulation, the vehicle sets up a 0.500 second time frame during
which it calculates the ground time.  The following list shows the
relationship of the ground time to the mode chosen:
        Msec                Mode
    0 - 35.7                 Normal state
    35.8 - 107.1          ALDL Mode 1
    107.2 - 178.6        ALDL Mode 2
    178.7 - 250.0       ALDL Mode 3
    250.1 - 321.4       ALDL Mode 4
    321.5 - 392.9      ALDL Mode 5
    393.0 - 464.3      ALDL Mode 6
    464.4 - 499.9      ALDL Mode 7
There are some PWM Vehicles that have times that do not correspond to these
times. (e.g. some Cadillac vehicles)  Timings for various modes are presented
wherever these timings are in conflict with the correct data.

The third class of vehicles is called GM30.  This description can be found in
GM document XDE-5024 (see appendix d.)  [ Appendix d is considered GM
Restricted and is unavailable to non-GM personnel. - drb]

----------------------
I'm posting this to the DIY_EFI list to clear up the confusion. Sorry - - I
posted that piece long before I had this document excerpt to read over. - drb



Carmine wrote:

> Dan, in one of the diy_efi archives, you said:
>
> >If you use a 20K resistor instead of the 10 K resistor, your car runs in
> >"normal mode" instead of the diagnostics mode, but provides the 20 byte
> >data stream anyway.  The 3.9 K resistor puts your car in limp-home mode
> >with a backup spark and fuel control map.
>
> How did you find this?  Thanks.
>
> Carmine