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Does anyone have any info about the pins on a 1998.5 OBD port and where the wires go. I.E. Where the chassis and signal ground go. Im trying to diagnose a faulty smarty cable or faulty obd/truck wiring. I have a 2002 ecu and a rebuilt 1998.5 ECU. I purchased a flash file from smarty to flash the 2002 to my 1998.5. IThe smarty would connect to the ECU while it was connected to the 2002 donor truck. IT wont on my truck. It wont connect to the 1998.5 or 2002 ecu while on my truck. I can hook my scan tool up to my truck and it will connect to both and read codes on both? SOOOOO I think something might be wrong with my obd port.

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ccd.jpg

 

 

the obd plug is on the right, the left is what goes where.  You will have to learn to read them to get through your issue.

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SCI - Serial Communication Interface
SCI consists of:
– Dedicated point-to-point, dual-wire, nonmultiplexed
serial communication interface
– Supports both diagnostics and flash reprogramming
capability
– Supports multiple baud rates to accommodate
both the low-speed diagnostic command mode
(at 7812.5 bps) and the high-speed parameter
interrogation command mode (at 62,500K bps)

• With the key ON:
• No scan tool connected to the DLC; there should be 5 volts
at the Rx circuit.
• No scan tool connected to the DLC; there should be no
voltage at the Tx circuit.
• The scan tool connected to the DLC; there should be 12
volts* at the Tx circuit.
• The scan tool connected to the DLC and Engine selected
from the Select System menu; there should be 5 volts at the
Tx circuit.


* This is the default voltage for ISO-K. When the Engine is
selected from the Select System menu the tool will turn off the 12 volts
and apply 5 volts to attempt SCI communication

 

Flash Programming:
•Scan tool pulls voltage down when sending Data on Rx
•Scan tool raises voltage on Rx circuit to 20 volts (indicates flash)
•Module sends message back for error detection

Edited by Chris O.

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what are the rx and tx circuits? So I was correct on the smarty does use the sci transmit and sci receive wires to flash the computer. So I can hook a normal scan tool to the truck and it will read data and clear codes. I cannot hook the smarty to it and read codes or flash the computer. So My sci wires will support low rate but not high rate programming. how do i go about diagnosing this?

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4 minutes ago, Chris O. said:

SCI Rx (Receive)

SCI Tx (Transmit)

OH okay sorry for the silly question. Which pin is the ground so i can ground out my volt meter to test voltage.

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So Do i use the signal ground or chassis ground to test the sci pins? Im sorry for my very simple questions. I dint mess with electrical very much.

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This is actually good question i don't know, probably the Signal GND.

On gas engines the signal ground goes directly to PCM, not sure about diesel applications?

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3 minutes ago, Chris O. said:

On gas engines the signal ground goes directly to PCM, not sure about diesel applications?

 

Should be the same on the diesel as well.

 

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So a smarty uses the tci wires to flash the computer. The signal wires are connected to the PCM. Is there a ground for the pcm that i can clean?

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1 hour ago, Waydin_Stewart said:

Is there a ground for the pcm that i can clean?

 

Yeah... The passenger side battery terminal. All the ECM, PCM and VP44 get there ground from the passenger side battery NEGATIVE cable its self. 

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I got the battery cables off the 2002 truck aswell so I guess I could swap that cable into my truck. I will start my venture of wiring tomorrow when I get time.

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Chassis ground. Communication lines DO NOT terminate at chassis ground. They terminate in the module.

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I am not sure where the signal ground came from but both pins 4 & 5 go to chassis ground G105 from splice S126.

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oh boy. this is why i shy away from electrical stuff. Confuses me every time as I have 0 knowledge in the field haha. Okay so The tci Recieve and Transmit wires should not equal 5 and 12v yet they should add up to around 5v?

1 hour ago, jlbayes said:

My cheat sheet for sci says when added together they equal 5v.

 

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Correct. You should not see any where near 12v on either line. Again this is per my cheat sheet, they should equal 5v when added together. Let's make this simple. Red lead to pin 4 or 5, black lead to chassis ground OR one of the ground pins in the obd connector. What are your measurements? Exact readings.

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Correct 12v DC. The readings will help us try and better help you understand as well.

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