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OBD diagnostics

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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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    In your case you got broken wire or corroded plug somewhere (OPEN) high resistance. Take your meter leads and connect them together you should see numbers closer to 0~5ohms, which means low resis

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  • Author

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?

  On 10/24/2017 at 1:10 PM, jlbayes said:

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

 

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.

  • Author

Okay simple is key for me haha sorry. Very dumb question but I set my voltmeter to 12v setting correct?

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

  • Author

This picture says 6 and 7 are for sci? and i believe it shows pin 5 as ground?

 

ccd.jpg

If i probe pins 4 and 7 it shows 0 with probes oriented both ways

If i Probe pins 4 and 5 it shows .02 on my volt meter. So does that mean my pin 7 is dead?

Pin 4 black lead and pin 6 red lead reads -1.14

Pin 4 red and pin 6 black reads 1.14. So my pin 7 is dead on the port?

Pin 5 red and pin 7 black reads 0

Pin 4 red and pin 16 black reads 13.19 and is slowly going down im guessing to 12v since I just had the truck on.

I have my red and black wires bacwards i think haha. it says com in black and I have the red wire in it and it says (OHM signal)VMA*F

  On 10/25/2017 at 2:27 PM, jlbayes said:

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

 

Edited by Waydin_Stewart

Whooopsss. Sorry about that the pin numbers were stuck in my head.

 

Pins 6 and 7 were the ones you wanted. Again sorry about that and to add to your confusion.

 

This will help;

 

COMMUNICATION

Symptom: *NO RESPONSE FROM PCM (SCI ONLY)

POSSIBLE CAUSES

CHECK PCM POWERS AND GROUNDS SCI TRANSMIT CIRCUIT SHORTED TO VOLTAGE TRANSMISSION CONTROL MODULE SCI RECEIVE CIRCUIT SHORTED TO VOLTAGE SCI CIRCUITS SHORTED TOGETHER SCI TRANSMIT CIRCUIT SHORTED TO GROUND SCI RECEIVE CIRCUIT SHORTED TO GROUND SCI RECEIVE CIRCUIT OPEN SCI TRANSMIT CIRCUIT OPEN GROUND CIRCUITS AT DLC OPEN POWERTRAIN CONTROL MODULE

TEST ACTION APPLICABILITY

1 Perform the symptom Checking PCM Power and Ground Circuits in the Driveability category. Did the vehicle pass this test? All Yes → Go To 2

No → Repair as necessary. Perform POWERTRAIN VERIFICATION TEST VER - 1.

 

2 Turn the ignition off. Disconnect the PCM C3 harness connector. Disconnect the DRBIIIt from the DLC. Measure the resistance between ground and the SCI Transmit circuit. Is the resistance below 5.0 ohms?  

Yes → Go To 3

No → Go To 4

 

3 Turn the ignition off. Disconnect the TCM harness connector (if equipped). NOTE: If vehicle is not equipped with a TCM, answer yes to the question. Measure the resistance between ground and the SCI Transmit circuit. Is the resistance below 5.0 ohms?  

Yes → Repair the SCI Transmit circuit for a short to ground. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Replace the Transmission Control Module. Perform POWERTRAIN VERIFICATION TEST VER - 1. 44 COMMUNICATION TEST ACTION APPLICABILITY

 

4 Turn the ignition off. Disconnect the DRBIIIt from the DLC. Disconnect the PCM harness connectors. Turn the ignition on. Measure the voltage of the SCI Transmit circuit at the DLC connector. Is the voltage above 1.0 volt?  

Yes → Repair the SCI Transmit circuit for a short to voltage. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Go To 5

 

5 Turn the ignition off. Disconnect the DRBIIIt from the DLC. Disconnect the PCM harness connectors. Turn the ignition on. Measure the voltage of the SCI Receive circuit at the DLC connector. Is the voltage above 1.0 volt?  

Yes → Repair the SCI Receive circuit for a short to voltage. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Go To 6

 

6 Turn the ignition off. Disconnect the DRBIIIt from the DLC. Disconnect the PCM harness connectors. Measure the resistance between the SCI Transmit circuit and the SCI Receive circuit at the PCM connector. Is the resistance below 5.0 ohms?  

Yes → Repair the short between the SCI Transmit and the SCI Receive circuits. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Go To 7

 

7 Turn the ignition off. Disconnect the PCM C3 harness connector. Disconnect the DRBIIIt from the DLC. Measure the resistance between ground and the SCI Receive circuit. Is the resistance below 5.0 ohms? 

Yes → Repair the SCI Receive circuit for a short to ground. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Go To 8

 

8 Turn the ignition off. Disconnect the PCM C3 harness connector. Disconnect the DRBIIIt from the DLC. Measure the resistance of the SCI Receive circuit between the PCM C3 connector and the DLC. Is the resistance below 5.0 ohms?  

Yes → Go To 9

No → Repair the SCI Receive circuit for an open. Perform POWERTRAIN VERIFICATION TEST VER - 1. 45 COMMUNICATION *NO RESPONSE FROM PCM (SCI ONLY) — Continued TEST ACTION APPLICABILITY

 

9 Turn the ignition off. Disconnect the PCM C3 harness connector. Disconnect the DRBIIIt from the DLC. Measure the resistance of the SCI Transmit circuit between the PCM C3 connector and the DLC. Is the resistance below 5.0 ohms? 

Yes → Go To 10

No → Repair the SCI Transmit circuit for an open. Perform POWERTRAIN VERIFICATION TEST VER - 1.

 

10 Turn the ignition off. Disconnect the DRBIIIt from the DLC. Disconnect the negative battery cable. Measure the resistance between ground and both ground circuits at the DLC. Is the resistance below 5.0 ohms for each measurement? 

Yes → Go To 11

No → Repair the ground circuit that measured above 5.0 ohms for an open. Perform POWERTRAIN VERIFICATION TEST VER - 1.

 

11 If there are no possible causes remaining, view repair. All Repair Replace and program the Powertrain Control Module in accordance with the Service Information. Perform POWERTRAIN VERIFICATION TEST VER - 1.

 

  • Author

How do I remove the OBDII plug from the bracket in my truck so I can inspect the wires on the back.

Okay Im gunna try to decipher what all that is saying haha.

  On 10/25/2017 at 3:56 PM, jlbayes said:

Whooopsss. Sorry about that the pin numbers were stuck in my head.

 

Pins 6 and 7 were the ones you wanted. Again sorry about that and to add to your confusion.

 

This will help;

 

COMMUNICATION

Symptom: *NO RESPONSE FROM PCM (SCI ONLY)

POSSIBLE CAUSES

CHECK PCM POWERS AND GROUNDS SCI TRANSMIT CIRCUIT SHORTED TO VOLTAGE TRANSMISSION CONTROL MODULE SCI RECEIVE CIRCUIT SHORTED TO VOLTAGE SCI CIRCUITS SHORTED TOGETHER SCI TRANSMIT CIRCUIT SHORTED TO GROUND SCI RECEIVE CIRCUIT SHORTED TO GROUND SCI RECEIVE CIRCUIT OPEN SCI TRANSMIT CIRCUIT OPEN GROUND CIRCUITS AT DLC OPEN POWERTRAIN CONTROL MODULE

TEST ACTION APPLICABILITY

1 Perform the symptom Checking PCM Power and Ground Circuits in the Driveability category. Did the vehicle pass this test? All Yes → Go To 2

No → Repair as necessary. Perform POWERTRAIN VERIFICATION TEST VER - 1.

 

2 Turn the ignition off. Disconnect the PCM C3 harness connector. Disconnect the DRBIIIt from the DLC. Measure the resistance between ground and the SCI Transmit circuit. Is the resistance below 5.0 ohms?  

Yes → Go To 3

No → Go To 4

 

3 Turn the ignition off. Disconnect the TCM harness connector (if equipped). NOTE: If vehicle is not equipped with a TCM, answer yes to the question. Measure the resistance between ground and the SCI Transmit circuit. Is the resistance below 5.0 ohms?  

Yes → Repair the SCI Transmit circuit for a short to ground. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Replace the Transmission Control Module. Perform POWERTRAIN VERIFICATION TEST VER - 1. 44 COMMUNICATION TEST ACTION APPLICABILITY

 

4 Turn the ignition off. Disconnect the DRBIIIt from the DLC. Disconnect the PCM harness connectors. Turn the ignition on. Measure the voltage of the SCI Transmit circuit at the DLC connector. Is the voltage above 1.0 volt?  

Yes → Repair the SCI Transmit circuit for a short to voltage. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Go To 5

 

5 Turn the ignition off. Disconnect the DRBIIIt from the DLC. Disconnect the PCM harness connectors. Turn the ignition on. Measure the voltage of the SCI Receive circuit at the DLC connector. Is the voltage above 1.0 volt?  

Yes → Repair the SCI Receive circuit for a short to voltage. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Go To 6

 

6 Turn the ignition off. Disconnect the DRBIIIt from the DLC. Disconnect the PCM harness connectors. Measure the resistance between the SCI Transmit circuit and the SCI Receive circuit at the PCM connector. Is the resistance below 5.0 ohms?  

Yes → Repair the short between the SCI Transmit and the SCI Receive circuits. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Go To 7

 

7 Turn the ignition off. Disconnect the PCM C3 harness connector. Disconnect the DRBIIIt from the DLC. Measure the resistance between ground and the SCI Receive circuit. Is the resistance below 5.0 ohms? 

Yes → Repair the SCI Receive circuit for a short to ground. Perform POWERTRAIN VERIFICATION TEST VER - 1.

No → Go To 8

 

8 Turn the ignition off. Disconnect the PCM C3 harness connector. Disconnect the DRBIIIt from the DLC. Measure the resistance of the SCI Receive circuit between the PCM C3 connector and the DLC. Is the resistance below 5.0 ohms?  

Yes → Go To 9

No → Repair the SCI Receive circuit for an open. Perform POWERTRAIN VERIFICATION TEST VER - 1. 45 COMMUNICATION *NO RESPONSE FROM PCM (SCI ONLY) — Continued TEST ACTION APPLICABILITY

 

9 Turn the ignition off. Disconnect the PCM C3 harness connector. Disconnect the DRBIIIt from the DLC. Measure the resistance of the SCI Transmit circuit between the PCM C3 connector and the DLC. Is the resistance below 5.0 ohms? 

Yes → Go To 10

No → Repair the SCI Transmit circuit for an open. Perform POWERTRAIN VERIFICATION TEST VER - 1.

 

10 Turn the ignition off. Disconnect the DRBIIIt from the DLC. Disconnect the negative battery cable. Measure the resistance between ground and both ground circuits at the DLC. Is the resistance below 5.0 ohms for each measurement? 

Yes → Go To 11

No → Repair the ground circuit that measured above 5.0 ohms for an open. Perform POWERTRAIN VERIFICATION TEST VER - 1.

 

11 If there are no possible causes remaining, view repair. All Repair Replace and program the Powertrain Control Module in accordance with the Service Information. Perform POWERTRAIN VERIFICATION TEST VER - 1.

 

 

So I have a bad pcm now? The truck will run and drive fine. Or atleast I believe so haha. If you focus on the exhaust sound it will miss at random very very very slightly in the exhaust note but that could be from injectors or just how the 5" exhaust makes it sound. a PCM isnt that expensive but I really didnt want to spend 3-400 on one. All the other pins i tested to pins 4 and 5 tested with some kind of voltage except pin 7. So Either the wire is diead at the dlc connector or the wire is busted or my pcm is friend?

I personally do not think you have a bad pcm. I know what the diagnostic says. The obd connector has two catch tabs on the side. Release them and it will push towards the bulk head (firewall).

  • Author

Okay so I removed the dlc from the bracket. All the wires on the back seem to be fine visually. I dont see any nicks or scuffs or open insulation on any of them. 

  On 10/25/2017 at 6:43 PM, jlbayes said:

I personally do not think you have a bad pcm. I know what the diagnostic says. The obd connector has two catch tabs on the side. Release them and it will push towards the bulk head (firewall).

 

What is this powertrain verification it keeps referring too?

I got to step 8 and it reads 24.1 on 200k ohm setting and now im super confused. What is an open? and why would my recieve wire be messed up if it was my transmit wire that wouldnt read any voltage?

 

  On 10/25/2017 at 10:13 PM, Waydin_Stewart said:

I got to step 8 and it reads 24.1 on 200k ohm setting

Above 5ohms = out of specification, you've got 24100ohms.

Basically:

5ohms <  and less = good

5ohms > and more = no good (step 8 Is the resistance below 5.0 ohms? (24100ohms) = No → Repair the SCI Receive circuit for an open)

  • Author

what is an open?

  On 10/26/2017 at 2:25 AM, Chris O. said:

 

Above 5ohms = out of specification, you've got 24100ohms.

Basically:

5ohms <  and less = good

5ohms > and more = no good (step 8 Is the resistance below 5.0 ohms? (24100ohms) = No → Repair the SCI Receive circuit for an open)

 

In your case you got broken wire or corroded plug somewhere (OPEN) high resistance.

Take your meter leads and connect them together you should see numbers closer to 0~5ohms, which means low resistance (SHORT) this is what you are looking for after the fix.

    • Like 1
    • Author

    That means ive been testing all the ohms wrong them i guess. well back to square one or whatever step i need to go back too. How do i go about finding the short? I feel bad as to how misinformed and uneducated i am at wiring.

      On 10/26/2017 at 2:53 AM, Waydin_Stewart said:

    That means ive been testing all the ohms wrong them i guess. well back to square one or whatever step i need to go back too. How do i go about finding the short? I feel bad as to how misinformed and uneducated i am at wiring.

    You sound like a younger guy, so don't feel bad not knowing something, all this time wasted now will pay for itself later. There's a lot to learn we all still learning.

    • Like 1

    I have a lot of years invested into electrical diagnostics and it STILL teaches me lessons.

     

    From what I am reading you are testing the wire correctly unless I am completely overlooking something. The FASTEST way to change the circuit is run an over lay. So you would go from the obd to the pcm 3 with a new circuit. It would eliminate almost all of the potential for issue. I have seen a ton and I mean a TON of issues with the pins being pushed out of the obd connector.

    • Like 1
    • Author

    So you recommend running a wire from pin 7 of the obd port to pin 29 of the c3 connector to bypass the wire in the bundle? If it happens to be the pin in the obd port how do I go about repairing it? Swapping out the port?

      On 10/26/2017 at 1:06 PM, jlbayes said:

    I have a lot of years invested into electrical diagnostics and it STILL teaches me lessons.

     

    From what I am reading you are testing the wire correctly unless I am completely overlooking something. The FASTEST way to change the circuit is run an over lay. So you would go from the obd to the pcm 3 with a new circuit. It would eliminate almost all of the potential for issue. I have seen a ton and I mean a TON of issues with the pins being pushed out of the obd connector.

     

    You answered my question about me missing something. That diagram shows pin 7 goes to pin 27 on the pcm c3 and pin 36 of the ecm. As well as the diagnostic is not specific about pinouts. Pin 29 at the pcm goes to pin 14 of the dlc. Has diesel labeled on the circuits. This picture will show you what I mean. The pins are the same number but different wire colors. These old diagrams suck.

    pins.JPG

    • Author

    If I probe pin 7 on DLC/OBD and pin 27 on c3 connector I get between 36.9 and 38.1 on 200k. If I use lower ohm reading it just says 1. Im even more confused now. So are the steps you provided for diesel or gas?

      On 10/26/2017 at 1:55 PM, jlbayes said:

    You answered my question about me missing something. That diagram shows pin 7 goes to pin 27 on the pcm c3 and pin 36 of the ecm. As well as the diagnostic is not specific about pinouts. Pin 29 at the pcm goes to pin 14 of the dlc. Has diesel labeled on the circuits. This picture will show you what I mean. The pins are the same number but different wire colors. These old diagrams suck.

    pins.JPG

     

    I get no voltage or ohm reading going from pin 7 on DLC/OBD to pin 36 on ECU connector.

    Both, it is a generic diagnostic.

     

    You are still measuring high resistance in that circuit. 1 on a low scale of a boat load of different dmm's signifies the circuit is open. It is pin 36 or 38. That diagram is fuzzy af. Pin 38, confirmed on my OEM diagram here at work. 

     

    It still does not change the fact you have high resistance between the pcm and the obd connector. 

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    Welcome To Mopar1973Man.Com LLC

    We are privately owned, with access to a professional Diesel Mechanic, who can provide additional support for Dodge Ram Cummins Diesel vehicles. Many detailed information is FREE and available to read. However, in order to interact directly with our Diesel Mechanic, Michael, by phone, via zoom, or as the web-based option, Subscription Plans are offered that will enable these and other features.  Go to the Subscription Page and Select a desired plan. At any time you wish to cancel the Subscription, click Subscription Page, select the 'Cancel' button, and it will be canceled. For your convenience, all subscriptions are on auto-renewal.