99 XJ OBD Data Port Wiring

For some reason my data port has gone dead. No power or signal to activate a scanner. Does anyone have a wiring diagram for the port or suggestions on things to check?

Thanks.

I'd start with checking the fuses. There's a 15a fuse that feeds it directly. Does the engine not run?

The only fuse I’m aware of is in #17 I think. Either way, the fuse is good. The Jeep and engine run fine, the light comes on as a trans code during certain times with the Atlas case. Same with the Rad Designs shifter when switching back into auto mode. Typically when done riding I clear the trans code.

Have you checked the obd port for power and ground at the plug? It could be a bad ground, which is common on older vehicles like these.

I had a similar issue on my ‘99 a couple of years ago. I couldn’t get any obd data at all using an ELM327 dongle and Dash Commander phone app. I was at a loss and was sure the obd port was somehow dead. Eventually, I figured out the problem was with the app, not the obd port. So If you haven’t tried another code reader device or app, that’s worth a shot.

A fuse or dirty/loose ground would be my first suspects.

It's important to determine if the code reader will power up when plugged into the DLC or if it cannot communicate with the PCM.


The DLC uses power from fuse #17 in the PDC to power the code reader/scanner, but the problem is that if F17 is blown, the headlamp switch won't be powered either. Cavity 16 on the lower right of the data connector is 12 volts positive. Not being able to "Communicate" is an issue with the Serial Communication Interface (SCI) function of the PCM.

The Data Link Connector (DLC) provides a ground circuit for the code reader via two pin cavities in the DLC, both of which are at the oil dipstick tube mount bracket on the right side of the engine. If these grounds are corroded, or disconnected, the DLC won't power up the code reader.

There are two pin cavities on the DLC that are SCI dedicated for the code reader to communicate with the PCM to retrieve DTC codes. There have been occurrences where the ABS CAB had a defective PCI connection and shut down the entire SCI circuit and the code reader could not communicate with the PCM.



Go to an auto parts store and get the code(s) read, the problem may be the code reader you are using.

Code scanners are good. The one that rides with the Jeep was tested on my truck once I got back to camp and it activated and functioned normally. Upon arriving back home, I put my second scanner on the Jeep port and no communication. I will check out the power and grounds tomorrow. If it’s not them, any further info on the signal pin outs where I could at least run a jumper to the PCM?

Thanks for your time.

The ground for the OBD port is attached to the stud that hold the dipstick, check that and see if it's loose or dirty.

Forum policy prevents posting copyrighted materials from the Service Manual, but a simple Google search will find the Service Manual page with the pin out info.

Search : Jeep OBD-II DLC pin out

Ended up being no 12v to the port. I ran a jumper to power and the scanner fires up and communicates normally. At least the data circuit is good. Ground is good to go. Fuse #17 is good and has voltage. So what else is on that data port circuit that I can check before beginning a trace? I also realized last weekend that my headlight switch and circuit has become erratic. I have to find a certain sweet spot in the running light position in order for the running lights and dash lights to come on. No go for either once in the headlight position. My existing switch did this along with two different Napa switches. I haven’t driven the Jeep at night in quite a while, so I do not know how long that problem has been around. And neither has the need arisen to need the data port recently to know how long it’s been dead, so I would wager the two issues could be related. The switch issue is interesting though as the problem seems to be within the switch itself. The connector has 12v and jumping power to the running lights all activates normally.