Dan's ALDL Information Page:


Here's to the beginning of On-board Diagnostics...
Note: Here is the title page for the source document. It is believed that there is no copywrited material in this document, and thus was open to transcription to HTML.  The GM restricted appendices have not been transcribed into this HTML document.  The address for Dr. Smith is no longer current. 

Good links: Peter Gargano is located in Australia, and researched how Holden systems work. They are derived from the domestic GM ALDL, and Peter's site has lots of valuable information. This includes software for reading the ALDL bus. Check out: Peter's ALDL page

 
Assembly Line Data Link Information For 1982 - 1986 General Motors Vehicles   Foreword:

All information contained in this document is based on the most recent [ 1986 ] data available. 
Revisions be made to this document when data becomes available.  NO warrantees or guarantees are made 
regarding the accuracy of the data contained in this document.  If there are any problems, please report 
them to:

Dr. Bradley Warren Smith
General Motors Corporation
Michigan Life Bldg, 3rd Fl,
Southfield, Michigan  48086
The appendices are classified GM restricted;

However, no other information in this document is known to be classified in any other way.

Bradley Warren Smith
1/13/86

 
 
Introduction: 

 It is the goal of this document to provide a comprehensive listing of the Assembly Line Data Link 
ALDL Information for the GM Vehicles between the years of 1982 and 1986.  The ALDL is a rename of 
ALCL thus the two terms are used synonomously here.  Included in this document is a description of the 
ALDL data streams for each system in each mode of operation along with the conversion factors necessary 
to use these data streams.  The pinout for the ALDL connectors is also stated in this document.

This document is ordered by year, engine displacement, fuel system, and producing division.

Thus, a 1984 Chevrolet 5.7 litre V8 engine would be referenced by: 1984 5.7 Litre TBI Chevrolet. 

In the case where there are two different data streams for a given engine, a letter classification will be added to 
describe which engines fit which ALDL system.

 
For each engine type, there is a pinout description, which can be used to determine which pins on the ALDL connector are used for what purpose.  The pins are referred to as A, B, C, etc.  This refers to the following format:
 
  F       E       D       C       B       A 
G       H       J       K       L       M
 
The sole exception to this rule is the 1981 J-car which has a five way connector which is numbered from left to right, as follows:    
 
Thus, for the purposes of this document, if the connector has twelve possible connections, it is numbered counter-clockwise starting from the “upper-right” corner.

 
Index to this document:
Preliminary Data
Temperature Sensor conversions
Load and TPS Conversion equations
Abbreviations
Varying ALDL modes on vehicles

Year    Disp    Fuel    Manufacturer 
1986    1.6     MIN     Chevrolet 
1986    1.8     TBI     Pontiac
1986    1.8T    MFI     Pontiac 
1986    2.0     TBI     Chevrolet 
1986    2.5     TBI     Pontiac
1986    2.8     CLCC    Chevrolet
1986    2.8     MFI     Chevrolet
1986    2.8     MFI     Pontiac
1986    2.8     TBI     Chevrolet 
1986    3.0     MFI     Buick
1986    3.8     CLCC    Buick
1986    3.8     MFI     Buick - non GM30
1986    3.8     MFI     Buick - GM30 ONLY 
1986    3.8     MFI     Oldsmobile - GM30 ONLY
1986    4.1     DFI     Cadillac - C Car 
1986    4.1     DFI     Cadillac - GM30 
1986    4.1     DFI     Cadillac - Fleetwood RWD 
1986    4.3     TBI     Chevrolet 
1986    4.3     CLCC    Chevrolet - Other
1986    4.8     CLCC    GM - Mexico
1986    5.0     CLCC    Chevrolet
1986    5.0     MFI     Chevrolet
1986    5.0     CLCC    Oldsmobile 
1986    5.7     CLCC    Chevrolet
1986    5.7     MFI     Chevrolet 
1986    6.2     DIE     Detroit Deisel Allison (Truck/Bus) 
1986    7.4     CLCC    Chevrolet 

Year    Disp    Fuel    Manufacturer 
1985    1.6     MIN     Chevrolet 
1985    1.8     TBI     Pontiac 
1985    1.8T    MFI     Pontiac - Turbo 
1985    2.0     TBI     Chevrolet 
1985    2.5     TBI     Pontiac 
1985    2.8     CLCC    Chevrolet
1985    2.8     MFI     Chevrolet
1985    2.8     MFI     Pontiac
1985    3.0     CLCC    Buick
1985    3.0     MFI     Buick
1985    3.8     CLCC    Buick
1985    3.8     MFI     Buick
1985    3.8T    MFI     Buick   - Turbo
1985    4.1     CLCC    Buick
1985    4.1C    DEFI    Cadillac - C Car 
1985    4.1     DEFI    Cadillac - RWD 
1985    4.3     CLCC    Chevrolet
1985    4.3     TBI     Chevrolet 
1985    5.0     CLCC    Chevrolet
1985    5.0     CLCC    Oldsmobile 
1985    5.0     TBI     Chevrolet 
1985    5.0     MFI     Chevrolet
1985    5.7     CLCC    Chevrolet
1985    5.7     MFI     Chevrolet
1985    6.2     DIE     Truck/Bus Diesel 

Year    Disp    Fuel    Manufacturer 
1984    1.6     CLCC    Chevrolet -- California 
1984    1.6     MIN     Chevrolet 
1984    1.8     TBI     Pontiac
1984    1.8T    MFI     Pontiac - Turbo 
1984    1.9     CLCC     ISUZU 
1984    2.0     TBI     Chevrolet 
1984    2.5     TBI     Pontiac 
1984    2.8     CLCC    Chevrolet
1984    3.0     CLCC    Buick
1984    3.8     CLCC    Chevrolet/Buick
1984    3.8     MFI     Buick
1984    4.1     CLCC    Buick
1984    4.1     DFI     Cadillac - C Car 
1984    4.1     DFI    Cadillac - RWD 
1984    4.1     TRK     Chevrolet
1984    5.0     TBI     Chevrolet 
1984    5.0     CLCC    Chevrolet
1984    5.0     CLCC    Oldsmobile 
1984    5.7     CLCC    Chevrolet
1984    5.7     TBI     Chevrolet 
1984    6.0     DEFI    Cadillac 
1984    6.2     DIE     Truck/Bus Diesel 

Year    Disp    Fuel    Manufacturer 
1983    1.6     MIN     Chevrolet 
1983    1.8     TBI     Pontiac 
1983    1.9     CLCC     ISUZU 
1983    2.0     CLCC    Chevrolet 
1983    2.0     TBI     Chevrolet 
1983    2.5     CLCC    Pontiac 
1983    2.5     TBI     Pontiac 
1983    2.8     CLCC    Chevrolet 
1983    3.0     CLCC    Buick 
1983    3.8     CLCC    Buick 
1983    3.8     CLCC    Chevrolet 
1983    3.8T    CLCC    Buick 
1983    4.1     CLCC    Buick 
1983    4.1     DFI     Cadillac 
1983    4.3     CLCC    Oldsmobile Diesel
1983    5.0     CLCC    Chevrolet 
1983    5.0     TBI     Chevrolet 
1983    5.0     CLCC    Oldsmobile 
1983    5.7     CLCC    Chevrolet 
1983    5.7     CLCC    Oldsmobile Diesel
1983    5.7     TBI     Chevrolet 
1983    6.0     CLCC    Cadillac 
1983    6.2     DEFI    Cadillac 

Year    Disp    Fuel    Manufacturer 
1982    1.6     FFS     Chevrolet  (California?) 
1982    1.6     MIN     Chevrolet 
1982    1.8     CLCC    Chevrolet 
1982    1.8     TBI     Pontiac 
1982    2.0     CLCC    Chevrolet 
1982    2.5     CLCC    Pontiac 
1982    2.5     TBI     Pontiac
1982    2.8     CLCC    Chevrolet 
1982    3.0     CLCC    Buick 
1982    3.8     CLCC    Buick 
1982    3.8     CLCC    Chevrolet 
1982    3.8T    CLCC    Buick 
1982    4.1     CLCC    Buick 
1982    4.1     DFI     Cadillac 
1982    4.3     CLCC    Oldsmobile 
1982    4.4     CLCC    Chevrolet 
1982    5.0     CLCC    Chevrolet 
1982    5.0     TBI     Chevrolet 
1982    5.0     CLCC    Oldsmobile 
1982    5.7     CLCC    Chevrolet 
1982    5.7     CLCC    Chevrolet Diesel
1982    5.7     TBI     Chevrolet 
1982    6.2     DEFI    Cadillac 

CLCC    -       Closed Loop Carburetor Control 
    DFI     -       Delco Fuel Injection 
    MIN     -       MINimal system 
    MFI     -       Multiport Fuel Injection 
    TBI     -       Throttle Body Injection 


 
General Information
 If “N” is the number on the data line, then the corresponding percent duty cycle can be calculated by dividing N by 2.56.  For example: 
NTRPMX, the engine rpm variable has a 25 RPM per bit resolution.  Thus, when the NTRPMX is 20, the engine is operating at 500 RPM. 
The range of this variable is 0 - 6400 RPM.
  FILTMPH is the actual miles per hour of the vehicle. 
The range of this variable is 0 - 255 MPH.
  The tables to convert ADTEMP and ADCOOL can be found below.  For the Chevrolet and Buick multiport fuel injection (MFI) systems, the conversion is linear, subsequently only the equation is given.  Load, LV8, and TPS information are also listed below.  Any engine that is an exception to these rules will contain appropriate conversion information.
 
Coolant Temperature Conversions
Chevrolet and Buick MFI: 

 If N is the value returned by the data stream in ADTEMP ( or ADCOOL), then the temperature in degrees Celcius is: 
C = (0.75*N)-40 
 

Degrees Farenheight =  (1.8 Degrees Celeius) + 32
 
 
CLCC (ALL)
ADTEMP Celcius
255 -38
253 -16
249 -5
244 5
237 15
228 25
215 35
198 45
179 55
158 65
136 75
115 85
95 95
86 100
78 105
70 110
63 115
57 116
0 186
 
 
TBI(ALL), and Pontiac MFI(TPI)
ADTEMP Celcius
255 -40
251 -30
250 -25
247 -20
245 -15
241 -10
237 -5
231 0
225 5
218 10
209 15
199 20
189 25
177 30
165 35
152 40
139 45
126 50
114 55
102 60
92 65
81 70
72 75
64 80
56 85
50 90
44 95
39 100
34 105
30 110
26 115
23 120
21 125
18 130
16 135
14 140
13 145
12 150
0 200
 

 
Load and TPS Conversions:
If LV8 is the load variable in counts, then: 
Vacuum = 80 - (5/16)*LV8 Kpa
1 ATM MAP = 20 + (5/16)*LV8 Kpa
2 ATM MAP = 30 + (5/8)*LV8 Kpa
TPS(in % open) = (25/64)*LV8
Load = (5/16)*LV8
MAP is an abbreviation for Manifold Absolute Pressure (sensor)  
Common Abbreviations:
Every attempt has been made to define the abbreviations that are used in this document.  It is, however, possible that some abbreviations are used without being defined.  The following is an expansion of several comon abbreviations:
 
Abbreviation Description
A/C Air Conditioner
AIR Air Injection reactor
A/D Analog to digital converter
ALCL Assembly Line communication link (Same as ALDL)
ALDL Assembly Line Diagnostic Link
BARO Barometric Pressure
CCC Computer Command Control
CCP Charcoal cannister purge
CLCC Closed Loop Carbeurator Control
CONV Converter
ECM Electronic Control Module
EFE Early Fuel Evaporation
EGR Exhaust Gas Recirculation
EKC Electronic Knock Control
EMR Electronic Module Retard
ESC Electronic Spark Control
EST Electronic Spark Timing
HEI High Energy Ignition
ISC Idle Speed Control
MAP Manifold Absolute Pressure
MFI Multiport Fuel Injection
M/C Mixture Control
PCV Positive Crankcase Ventilation
PFI Multiport Fuel Injection
P/N Park/Neutral
TBI Throttle Body Injection
TCC Torque Converter Clutch
TPS Throttle Position Sensor
PROM Calibration Unit
VIN Vehicle Identification Number
VSS Vehicle Speed Sensor
 

 
Varying Modes on Vehicles
 There are three classes of vehicles that have been produced by GM since 1982. 
[as of 1/86 - drb]

The first set of vehicles are those whose data streams are controlled by placing a resistive value from pin B of the ALDL connector to pin A of the ALDL connector.  The vehicles, called resistive control (RC) represent the largest portion of GM vehicles produced to date. [1986] These vehicles have the following modes: 

Normal mode     (R>=20K ohm) 
ALDL mode       (R==10K ohm)
Backup mode     (R==3.9 K ohm) 
Field Service     (R<=500 ohm) 

The latter mode is also called shorted mode.  These modes instruct the Electronic Computer Module (ECM) about what functions perform and what data to ship. 
 

 The second class of vehicles are those that are controled by shorting pin B to pin A.  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 cehicle  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
464.3 - 499.9 Diagnostic Mode
 
There are 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.  The description of these vehicles can be found in the GM document XDE-5024 (see appendix d). [Not included in this HTML.]
 One thing to note: Pre-1987 vehicles do not always use a TTL level signal to flash the byte codes. Some of the vehicles (like my 1984
 Trans Am) flash the "check engine" light instead. In this case, some ALDL scantool designs must be modified with a 5.1V Zener diode and a current-limiting 100Kohm resistor on the front-end. This will reduce the +13.8V signal level to a more manageable 5 Volt TTL-level. 


 There is a new site that recently came on-line. Peter Gargano is located in Australia, and researched how Holden systems work. They are derived from the domestic GM ALDL, and Peter's site has lots of valuable information. This includes software for reading the ALDL bus. Check out: Peter's ALDL page