i have a 2001 ram 1500 4x4 with 99k on it . im currently the second owner and im trying to restore the truck. My main problem at the moment is when i connect any type of scan tool to my obd2 port, they all end up coming back with "LINK ERROR". i have checked all of my fuses even #12 on the side of my dash. ive checked the fuse behind my cigarette lighter. I made sure all the wires are in the obd2 connector. there is nothing aftermarket on this truck. the truck runs and drives mint hasnt given me any problems at all. Truely stumped here. any help will be really appreciated

 

Chryslers of that generation use the ISO 9141/K-line protocol. That's a very simple single-wire protocol that only uses pin 7 and ground (pin 5). Pin 7 should be 12V when idle. Also check ground pin 5 (signal) and pin 4 (chassis) for resistance/voltage drop to the battery. Pretty much all OBD2 testers should speak the protocol but newer ones might get confused auto-detecting the connection. If the tool has an option to select a protocol try that as well.

 

I only checked if i had power to the pin7 when i had the key turned. i had no power to it at all. tomorrow im going to check pin 7 again for 12v when the trucks idling. But for the grounds they both had resistance, so im leaning more to the sci receive wire either being snagged somewhere or slightly out of my pcm connector. ive had that happen to me before with my other dodge. Thanks brotha ill get back to you tomorrow

 

Sorry, "idle" meant no communication going on, not the engine idling so you already covered that. If you don't see 12V with the ignition on that's a problem. Trace the pink/dark blue wire from pin 7 to the PCM connector 1 pin 27. It runs through the big connector in the cowl and the funky big square connector in the PDC.

As you mentioned SCI, that's something super screwy about how Chrysler has implemented this. They use pin 7 for bi-directional K-line for OBD2 purposes, and pin 7 and pin 6 for the Chrysler specific SCI bus. In K-line mode the available data is limited to standard OBD2 pids, in SCI mode there is much more data available and it supports active tests with the PCM (idle set, injector tests etc.). Just something to be aware of.

 

So i traced the pink/dark blue wire back to the PCM and back probbed it there to see what i had for a voltage and i have about .04v coming out of the pcm. so im guessing my pcm is fried? im not the best with eletrical but im trying to figure it out so please bare with me.

 

So i traced the pink/dark blue wire back to the PCM and back probbed it there to see what i had for a voltage and i have about .04v coming out of the pcm. so im guessing my pcm is fried? im not the best with eletrical but im trying to figure it out so please bare with me.

 

My apologies I have sent you on a bit of a wild goose chase there. Just checked it on my truck and the pink/dark blue wire only sees voltage from the test tool, not the PCM. The procedure is still the same, check for 12V all the way to the PCM just with the OBD2 tool connected.

 

So i started by back probing the pink and dark blue wire at the obd2 port itself with my scan tool connect and i wasnt getting any voltage at all. So just to make sure my tester was working i back probbed the dark green wire ( the SCI recieve i believe ) and was getting a constant 4.19v. So i do believe my tester is working correctly, and while i was looking i realized my obd2 port has 8 wires going into it, now the diagram i have shows there should be only 7. The "8th wire" if i should call it that is white with purple stripes, and its in pin #14 on the obd2 port. So now i dont know what to think. Again thank you brotha

 

I checked my truck and it has the same wire on pin 14. The FSM shows it for the diesel trucks but Chrysler probably just used the same wiring harness inside the cab across all models. But yes the wiring diagram shows only 7 connections for a gas engine.

When I was checking my truck yesterday I connected/disconnected the OBD2 reader multiple times and consistently the voltage came and went with it. So I still believe your problem is with the signal on the pink/dark blue wire from pin 7. Two possible problems:
- The wire from pin 7 gets pulled to ground somewhere (basically a short to ground). With everything off/ key out, what is the resistance to ground on pin 7 ?
- There is something wrong with the ground connections and while the OBD2 tool powers on it somehow can't get the signal level up.

What OBD2 tools did you try, and is the truck in/from the rust belt area ?

 

So i just got home from work im going to check the grounds for what the resistance is. And yes sadly the truck is from the rust belt area. I live in RI so no way around it. But im currently using your basic 40 dollar scan tool. Not a decent one that powers itself.

Okay so i check the resistance on the grounds, the black and tan wire in pin #5 which i believe is grounded to the front of the motor had 2.5 ohms, the light green and black wire in pin #4 which i believe is grounded on left kick panel next to the fuse box, wasnt showing me anything.