hey u guys and girls have an 88 c4 having problems with datalink connector diagnostic computer says power problem with connector have bought books on car but sofar none show good wiring diagrams so i can pin point problem any suggestions or answers if anyone has had same problem need to reset check engine light and also check abs problems

 
           
There were at least three different connectors used with ALDL. General Motors implemented both a 5-pin connector and a 12-pin connector, with the 12 pin connector being used in the vast majority of GM cars.( Lotus implemented a 10-pin connector.) The pins are given letter designations in the following layouts (as seen from the front of the vehicle connector):
12-pin ALDL connector pinout:

F E D C B A

G H J K L M

10-pin ALDL connector pinout:

A B C D E

K J H G F
5-pin ALDL connector pinout:

A B C D E
Note the difference in pin ordering between the connectors and the fact that the letter I is not used. Unfortunately, the definition of which signals were present on each pin varied between vehicle models. There were generally only three pins used for basic ALDL —ground, battery voltage, and a single line for data—, although other pins were often used for additional vehicle-specific diagnostic information and control interfaces. No battery voltage is present in the 12 pin ALDL connector., which your '88 should have.
The scan tool communicates over the E terminal for data only. If you jumper the "A" and "B" terminals, you should be able to see the check engine light "flash" the codes. It will start with one flash, followed by a short pause, then two quick flashes...this is code "12", which signals that the ECM is in diagnostic mode. It will flash the individual codes three times, then move on to the next stored code. If there are no codes stored, the "12" code will flash repeatedly.


Make sure the "A" terminal is a good ground...this is a fairly common issue with scam tool communication problems...
hth
Adams' Apple2009-08-24 09:32:49

thanks will try recomended advice and see what happens thanks once again will talk cars later

I have the wiring diagram that does show the ALDL connector wiring, if it will help. I can e-mail to ya this evening.
What it shows, by terminal #, is...
A= Ground
B= ALDL data from ECM/codes only
C= Canister purge solenoid(for testing)
D= Not used
E= Serial Data(for scam tool data)
F= TCC(automatic trans) or O/D relay(standard trans)
G= Fuel pump

Terminals G, F, and C are useful for inserting a test light, to see if the component is getting a command from the ECM. For instance, if you want to know if the trans is getting a command for O/D, you would put the test light into the "F" terminal of the ALDL connector, and ground the other end of the light. While driving, if the ECM commands the O/D relay on, the light will light up, showing the ECM has actually made the command.

hth

thank u once again tried a/b terminals got the results i needed but it did not give me the abs codes, been having a pulsation from pedal almost at  when stopping at a light hearing abs noise from abs controls behind drivers seat light for abs comes on sometimes but will reset after car is shut off and restarted, when pulled codes with flash codes nothing for abs? the two codes i got were 13 and 34 which is maf34 and o2 left bank which were old codes from when i first got car and have since been repaired

Dang...I forgot about the ABS problem. I think the ABS codes are available from a different connector in the rear compartment. I'll double check that in the morn and post the info. I don't have my Mitchel/Alldata computer set up here at home...don't have any place to put it at the time!   I'll get it from the shop 'puter tomorrow...sorry!


Your ABS pulsing when almost at a stop sounds like a bad wheel speed sensor. That's kinda how they do when they're on the edge of failing...they tend to loose the signal at slow speeds, and when that happens, the ABS module thinks the wheel is sliding(or on the verge), so it activates the system.
Adams' Apple2009-08-25 19:55:45

cool thats what i thought wheel sensor will have to see which one it is

I made this thread a "sticky", since it shows the ALDL connector, and other neat info for the early OBDI systems. This will help some folks when it comes down to answering the question "What codes does it have?".