ALDL revealed

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 Smith is no longer current.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