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Scan your OBD-I 6.5 for $2.55

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23K views 43 replies 16 participants last post by  livin65 
#1 · (Edited)
FYI, the absolute cheapest way to scan your 94-95 Truck

*Notice: You need GMTD Scan Tech PRO to send commands such as TDCO Learn or injector balance tests (that isn't free)

What you need:

They are two of the wires in the RS232 (serial data) adapter you use to communicate with the PCM. Our PCM's are fairly forgiving so we don't need fancy adapters to connect up.

In the following ALDL pinout, you connect:

  • RX/TX to M (Serial Data)
  • GND to A (Ground)

(use your imagination here, you can solder to paperclips and shove them in, use an ALDL connector you have laying around, or tap directly into the corresponding wires in the ALDL plug)
Text Font Technology


Now, Open GMTD Scan Tech Basic and make sure you settings are for COM# your adapter is recognized on your computer, and the baud rate = 8192.


Here's what the cable looks like when you get it. I didn't list any wire colors since they might vary per manufacturer. The auction should tell you what is what:
Wire Cable Networking cables Electronic device Electronics accessory
 
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#2 ·
Interesting.
 
#3 · (Edited)
omfg sweeet, i have tons of usb cables laying around here lol. im goinna try this considering most ALL usb cables have same colors as this one, 2 5+V, gnd, term, data
 
#4 · (Edited)
Quadstar, thanks for the link, and info! That is WAY cleaner than my current arduino cable solution. (The "scan for less than $10" version)



Actually, that will not work. What quadstar posted above is a USB cable with an integrated USB to RS232 serial adapter "bridge" built-in. Looking at that cable, it is likely in the USB plug end.

The trucks don't "speak" USB, and won't be able to communicate to the computer without an "interpreter/translator" (the serial bridge in this case.)

I would not attempt just hacking the end off a USB cable and plugging it into the truck, as who knows what it may do to the PCM.

Matt
 
#7 ·
There's something to be said for that approach also. If you figure in the time you saved, it's about the same, and you can plug it right in and go.
 
#6 ·
Them bastards lol
 
#9 ·
So I got a question, my buddy has a ALDL cable for his '89 Trans Am for data logging, it also works on my '93 bird. Would that work on my '95 truck then too I assume? All are obviously OBDI. Then I could do it for free. :HiHi:
 
#10 ·
It depends. Some of them are re-wired to work with different ECU's or use multiple pins in the ALDL plug. It should work though, you aren't hurting anything to try it!

See if it has a switch on it to switch modes or post up a brand/part# on it.
 
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#12 ·
Nice find QS this is on my list of stuff to order as my arduino cable set up is getting beat up! Thx
 
#14 ·

They are two of the wires in the RS232 (serial data) adapter you use to communicate with the PCM. Our PCM's are fairly forgiving so we don't need fancy adapters to connect up.


Here's what the cable looks like when you get it. I didn't list any wire colors since they might vary per manufacturer. The auction should tell you what is what:
off the auction page:
"Black --- GND, Green --- RXD, White --- TXD, Red --- +5V

Operating frequency is 12MHZ, suitable for USB 2.0 communication protocol
PL2303HX a 28-pin SMD SOIC package
Directly to the USB signals into serial signals
Baud rate from 75?1228800, there are 22 kinds of baud rate can choose
A total of five kinds of data to support 5,6,7,8,16 bits
Length of the cable: 120 CM

USB Serial Cable
Chip Prolific PL2303HX

Note:this item does NOT support windows 8 system"


 
#15 ·
#16 ·
No worries about the windows 8! I have the gmtdscan scan on a laptop that's older than my son and he's 11! Did they have something before windows cause that's prob what I'm running. Haha
 
#17 ·
well, then i guess im just going to order the cable lol, $2.55 on Ebay here i come!!!!!! lol
 
#20 ·
#21 ·
#22 ·
FYI, the absolute cheapest way to scan your 94-95 Truck

*Notice: You need GMTD Scan Tech PRO to send commands such as TDCO Learn or injector balance tests (that isn't free)

What you need:

They are two of the wires in the RS232 (serial data) adapter you use to communicate with the PCM. Our PCM's are fairly forgiving so we don't need fancy adapters to connect up.

In the following ALDL pinout, you connect:

  • RX/TX to M (Serial Data)
  • GND to A (Ground)

(use your imagination here, you can solder to paperclips and shove them in, use an ALDL connector you have laying around, or tap directly into the corresponding wires in the ALDL plug)
View attachment 288609

Now, Open GMTD Scan Tech Basic and make sure you settings are for COM# your adapter is recognized on your computer, and the baud rate = 8192.


Here's what the cable looks like when you get it. I didn't list any wire colors since they might vary per manufacturer. The auction should tell you what is what:
View attachment 288617
Added to FAQs :thumb:
 
#23 ·
Good deal, Freddy

FYI there's no danger here as far as sparks or anything. Just don't go touching the 5v wire out of the adapter to anything.

I'm going to solder a 2 pin plug up and put it in my dash for a permanent type setup.
 
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#24 · (Edited)
perminant setup sounds like a good idea, i was actually thinking on running it and hiding it under the carpet to my center counsel, i have a usb port that u wire into a wall and soldier the wires to, im thinking on making a plug in the counsel so i just have to plug a USB attachment cable directly to my laptop and can unhook and no wires around.
 
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#29 ·
I don't know if a usb header will work for what you want to accomplish here. I'm just going to use a 12v bullet style power connector. Center is GND, outer area is Serial Data.
 
#25 ·
Update, I tried my buddies 86-95 GM ALDL cable and it worked! After I messed around for an hour trying to find a driver for it.... But anyway got to work perfect and see whats going on with my truck via GMTDscan basic. :thumb:
 
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#26 ·
guess Im gonna have to try, just got me a new laptop, my daughters electronic hand me downs... now if I can just figure out how to turn it on :hehe:


until then, I still got my trusted PC...
 
#27 ·
#28 ·
On this USB cable:

Do we connect RXD/green and TXD/white together for M (serial data)?

Thanks
Yes, they go together.

Dont use the +5v for anything. just cap it off so it doesn't ever ground.
 
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#30 ·
I've been looking at this and believe I can use my phone with an rs232 adapter cable and a program I found called ALDLdroid to check codes on my suburban, I'm going give it a try, the program is $20 but it might be a lot easier than using my laptop and it looks pretty slick. Im curious how it compares to gmtdscan basic. Im sure it probably wont be able to perform the functions of the pro version. I've been trying to figure out if the elm327 bluetooth adapter is compatible with the 8192 baud aldl protocol if it is used with an adaptor with the correct pins but I'm not sure. I know that it works on my Ducati with the right cable.
 
#31 · (Edited)
Its not going to do diddly squat with out a valid tunerpro .adx file. They aren't floating around that I know of but I'd love it if you have it :thumb:
 
#32 ·
Ahhh I got ya, I assumed they were relatively common like other ecu's. After a few minutes on the Google I saw a few common names pop up so I'm assuming they're out there, I've never played with tunerpro, but it might be fun.
 
#33 · (Edited)
FYI, the absolute cheapest way to scan your 94-95 Truck

*Notice: You need GMTD Scan Tech PRO to send commands such as TDCO Learn or injector balance tests (that isn't free)

What you need:

They are two of the wires in the RS232 (serial data) adapter you use to communicate with the PCM. Our PCM's are fairly forgiving so we don't need fancy adapters to connect up.

In the following ALDL pinout, you connect:

  • RX/TX to M (Serial Data)
  • GND to A (Ground)

(use your imagination here, you can solder to paperclips and shove them in, use an ALDL connector you have laying around, or tap directly into the corresponding wires in the ALDL plug)
View attachment 288609

Now, Open GMTD Scan Tech Basic and make sure you settings are for COM# your adapter is recognized on your computer, and the baud rate = 8192.


Here's what the cable looks like when you get it. I didn't list any wire colors since they might vary per manufacturer. The auction should tell you what is what:
View attachment 288617
I am adding what I did:

I bought the USB cable, shown above.

I bought a OBD1 12 pin - OBD2 16 pin adapter

I removed the 16 pin OBD2 end and strain relief

I found the Red OBD1 wire is A and the Black OBD1 wire is M with an ohm meter, then cut back the other 2 wires.
I soldered & crimped :rolleyes: the Green & White USB wires to the Black OBD1 wire. Then soldered & crimped the Black USB wire to the Red OBD1 wire. I shrink wrapped the red USB 5v wire.

Wrapped up enough that if it does get tugged, it will not damage the wiring.



The USB & OBD cables came out of China and cost me less than $8.
 
#34 ·
#36 ·
You only have a TCM (transmission control module). GMTDSCAN should see all the transmission data, however. Yes, the plug is the same.
 
#38 ·
I think you need a driver software.

I am not sure what driver though since it has been a few years ago.
 
#41 ·
#42 ·
Just ordered a cable. So do both the Rx and Tx go into the serial pin or just one?
 
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