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Hi, I tried searching for this,but to be honest not sure how to phrase my question. I would like to know if the (2) data wires - canbus wires can be "split"? so the the 2 OG wires at the ECM can continue with normal functions and then 2 split wires can be ran to another data point? I know this is a weird question... my ultimate goal/question is to try to run a separate set of data wires directly to the obd port from the ECM
background: ECM- 2013 x38 (2013 chevy truck) DATA WIRES- 2500 (TAN/BLK) AND 2501 (tan)
my colors might be switched
Yes that should be fine. That's exactly how the oems do networking.
Edit- Is this in a swap?? The can wires really just relay info from 1 module to the rest. So the instrument cluster can get the engine data without having wire ran to each individual sensor. If this is a swap the can circuit don't have any other modules to talk to anyway.
I have always thought of the 2500/01 circuit as a continuity check. The resistors at both ends of the circuit are what is important and if the proper resistance isn't observed, nothing works, including your scanner.
lsxford, yes this happens to be a swap ('86 c10-'13 4.8 stock swap) I was thinking that I could do what I mentioned, but being "data wires" was not sure if circumstances would be different?
pcguy, thanks for the info. so... if I understand then, each of the physical wires (along the wire) there are physical resistors? maybe that is my issue? basically I get intermittent reading issues from my port. I have done continuity tests and at curtain portions (between connectors) the test is good & in other portions it is hit/miss. it appears that the engine runs fine & sounds good, but I am getting errors with my D D dash gauges (the BIM module can't comm.)
There are only two 120 ohm resistors, one at each end of the circuit. In my Chevelle restomod project (2014) camaro ss, it was very helpful to know where the two resistors were located.
A CAN bus terminator can be used for termination of any high speed (ISO 11898-2) CAN bus system. The 120 Ohm terminating resistor is setup between pin 2 (CAN low) and pin 7 (CAN high). In general, ISO 11898-2 CAN networks must be terminated at each end using 120 Ohm terminal resistors.
At any point where the 2500/01 circuit appears, there should be a reading of 60+- a couple of ohms (two 120 ohm resistors in parallel will read 60 oihms). If the reading is 120, one of the resistors is missing...
Nick, thanks! I am going to check the readings and double check my continuity tonight/tomorrow. I want to make sure my simple mind is understanding correctly. so does the 2 (2500/2501) circuits each need to read 60ohms from the ECM to to each endpoint (my DLC) specifically? also if i run a seperate set of twisted pair from the data wires (2 circuits) to the DLC (obd port) do I need to wire in a 60ohm resistor at either end or 2 120 ohms (to get 60 ohms) at each end before the ends? I thank you for your time and patience
There are only two 120 ohm resistors, one at each end of the circuit. In my Chevelle restomod project (2014) camaro ss, it was very helpful to know where the two resistors were located.
A CAN bus terminator can be used for termination of any high speed (ISO 11898-2) CAN bus system. The 120 Ohm terminating resistor is setup between pin 2 (CAN low) and pin 7 (CAN high). In general, ISO 11898-2 CAN networks must be terminated at each end using 120 Ohm terminal resistors.
At any point where the 2500/01 circuit appears, there should be a reading of 60+- a couple of ohms (two 120 ohm resistors in parallel will read 60 oihms). If the reading is 120, one of the resistors is missing...
Nick
First 2500/01 is one circuit not two and if at any point you take a resistance reading like on the OBDII location where the pins are readily available, the reading should be 60 ohms. If the reading is 120 ohms, the circuit is open somewhere; can't begin to tell you how the circuit travels bc they are all different.
Not recalling the nature of the issue, but if the engine cranks the problem is not with the 2500/01 circuit. Any addition to that circuit needs to be in series with the existing wiring and the result must not effect the.60 ohm reading.
As for your project question, having a hard time envisioning what you're trying to accomplish...
NICK, thank you for the reply, I guess I get confused because the diagrams and ECM pinout indicate circuit 2500 and circuit 2501, my lack of knowledge thought each was a separate circuit. the engine starts & idles fine - all appears to be good there, I can drive in the neighborhood. Basically I am trying to install my DD dash (BIM module) and it is unable to communicate with the ECM (cycling thru J-F-C). I tried to verify that the OBD port was correct & that is when I discovered that the port would work intermittently. the code reader would sometimes connect & then not connect. I am "concluding" that I must have a bad wire connection somewhere? so I am trying to verify that the wires are good from the ECM to a connector (X109 connector) then from there through the F/W to my OBD port. I can trace (see) the wires from the ECM to the connector and then from the connector to the new OBD port. the port worked during initial wiring, but after some time & other work it now appears that the conn. may have been jostled too much? my idea is to just tap (solder) into the the wires a few inches from the ECM out and just run 2 new (twisted pair) directly to the OBD port?
thank you again for your patience and any info. you help with.
NICK, I had a friend help me with the suggestions that you had given & when all said and done, I was able to get the 60k ohms (63.7k ohms) across the 2500/01 circuit(s)? my friend suggested that i might have a weak or bad ground that might be causing the interminttent readings/access.of the obd port. I will check that in the next day or so. hopefully if anything that will fix it. FYI it appears that the resistor(s) are in the actual J1 connector to the ECM. we did a check across the 2 pin slots & got the 60+/- reading.
thank you again for your help & any future suggestions... I will keep a look out for updates on the chevelle build
FTR, the 60 OHM reading can be taken at any access point along the circuit route. If you open the circuit anywhere along the route, you will see 120 ohms looking in both directions. The location of the resistors is not fixed, but they will always be at the ends of the circuit. So if you are adding something to the circuit, you will need to connect it in series, thereby keeping the resistors at the ends of the circuit.
Also, I recall that one of the resistors is commonly found at the point where the fuel pump controller is located.
well I was able to find a pinout for the x109 connector. I found that in my connection I did not (thought i did) make the ground connection. so... i cut the wire from the connector & soldered a wire to it & then ran it directly to the chassis. i checked t osee if the DD gauges could communicate & it appears to be all good now. ( i checked it 3 different times) so for now... i think all is right again. in general (if i understand right??) the circuit was just communicating slower at 120k than at the required 60k ohms? so my code reader would spend more time trying to communicate as opposed to the BIM would just do a quick "scan". not sure if my thinking is right?....
Well I thought that I might have fixed the issue, but…. It appears that I have not. After doing some research using my very limited wiring knowledge, along with help from friends/board members, I believe to fix the issue I need to install a 120ohm resistor at the obd2 port end. If I understand correctly, doing this will get me to the correct/desired 60ohm “reading” at my obd2 port. My thought to do this is to de-pin the data wires and bring back thru the F/W – so to have room to solder the resistor between the wires wrap everything and then run back thru F/W and re-pin to port. Any suggestions or guidance would be very appreciative.
Thanks!
Think we need to back up a bit... What is the ohm reading you get on the 2500/01 circuit? Normally, If the reading is not somewhere near 60 ohms, nothing works; but it sounds like your project has modified the wiring significantly.
After stating that you got 63.nn ohms, you now say you think you need to add a 120 ohm resistor. That makes me think you have not located both of the existing 120 ohm resistors; if there is only one you would never have gotten a good 60 ohm resistance.
Maybe you should state the issue as it currently exists. You say the engine runs fine but something is not communicating as you think it should be. The engine would not run if the 60 resistance was not present nor would anything else work, ie scanner, fuel pump, etc.
You don't need a third 120 ohm resistor, but need to understand why the engine runs but the desired communication is not working. If this is simply a bad connection, it could be somewhere unrelated to what we are discussing and is very likely associated with the wiring changes made to the original harness????
nick, thank you for the reply. I know I am not stating the problem correctly... I am not sure how to explain what the initial problem was, other than I could get my code reader to read sometimes... but my dakota digital dash BIM would not communicate at all. The engine runs fine and all engine systems are working properly.. your initial problem solution appears to have been the correct solution. After a few days of investigating I was able to determine that there was a 120ohm resistor at the ECM plug only (I needed another resistor at the end of the canbus). This past weekend I bit the bullet & with guidance from here & friends I de-pinned the data wires from the OBD2 port (my end of the canbus) and after gently "de-skinning" a portion of both wires I soldered a automotive 120ohm resistor a few inches from the OBD2 port termination. I checked the ohm reading at the ends and was consistantly reading 62.3- 62.5 ohms. I plugged the BIM module in & reconnected the power, I turned the key on and the gauges all appear to be working..... WOW!! RELEIF! I started the truck & all the gauges were operating.I then coated everything in "liquid electrical tape" and then wrapped that in regular electrical tape. I started the truck again & the gauges are still operating correctly - I also connected the code reader & it also connected right away.... relief!...LOL!
NICK- thank you for your time and patience. I am not (obviously) a electrical guru so my explainations and terms are not always correctly used. your suggestions & links were helpful and appreciated. thank you again for your assistance!
I hope that others will find this a help if needed. although I am gathering that most do not use the OG harness and equipment.
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can data wires question 
