OBD II not reading

[Simple Man]

I just went to smog my '98 XJ and failed due to the OBD II not putting out any signal. They needed a tach signal. My tack works fine. I've had the rig for five years and never had a smog problem. Rig runs fine.

I came home and sure enough, I couldn't get a signal from the computer with my AutoXray. Nothing in my books about troubleshooting this. I searched and couldn't find any help. Does anyone out there have an idea about what's going on?

I'm going to rundown the wires for breaks or disconnections. Check fuses, etc. and check back here after lunch.

Any ideas would be helpful. Thanks,

 

[Kejtar]

I just went to smog my '98 XJ and failed due to the OBD II not putting out any signal. They needed a tach signal. My tack works fine. I've had the rig for five years and never had a smog problem. Rig runs fine.

I came home and sure enough, I couldn't get a signal from the computer with my AutoXray. Nothing in my books about troubleshooting this. I searched and couldn't find any help. Does anyone out there have an idea about what's going on?

I'm going to rundown the wires for breaks or disconnections. Check fuses, etc. and check back here after lunch.

Any ideas would be helpful. Thanks,

There is a fuse in the fuse box under the hood that will cause that. IIRC it's one of the smallish looking ones.

 

[Simple Man]

I tried to find a fuse box diagram, couldn't. So, I pulled each fuse, one at a time. The fuses are all good.

Could there be an inline fuse under the dash?

 

[Kejtar]

I tried to find a fuse box diagram, couldn't. So, I pulled each fuse, one at a time. The fuses are all good.

Could there be an inline fuse under the dash?

Does the backlight in your dash come up? Is your code reader giving you any errors?

 

[Kejtar]

I just looked at the FSM (it's from a 2000 model, but I think that fuse is same number in 98) and the one in question is fuse #19 in the Power Distribution Center under the hood.

 

[Simple Man]

The backlight on the dash works fine.

I've already pulled each fuse and each appears good. They're not numbered.

The check engine light is not on, so I assume there are no codes to retrieve.

The scanner will not read from the OBDII port, that's the whole problem. Somehow the port went dead.

 

[Kejtar]

The backlight on the dash works fine.

I've already pulled each fuse and each appears good. They're not numbered.

The check engine light is not on, so I assume there are no codes to retrieve.

The scanner will not read from the OBDII port, that's the whole problem. Somehow the port went dead.

There is a pin on that port that should deliver 12V. I don't remember which one, but if you go through them all (one lead from the multimeter on the ground another going through the pins) and you don't get 12V there's your problem. Since your fuse checks out ok, and the dashlights work fine (the dashlights are controlled through the headlight switch which is on the same fuse: btw it's nto the lights we're talking about it's the backlight for the whole dash) then the wiring might have break someplace between where the wiring splits off for the two. Also did your code reader give error codes (for the code reader itself. When my fuse blew I got an error code that came from the reader and when I called the tech support people for it, they told me it meant no 12v to the socket).

 

[Simple Man]

I'll go check for a 12 volt pin.

Yes, I know you meant the backlighting that comes on with the headlights.

The code reading came back with "connection broken" or "no connection made". I'll do it again and confirm what it says.

 

[Simple Man]

I've got 12 volts at the lower right connector as you look at the port under the dash.

The scanner reads "Loss of communication" then "Monitor Mode Exiting".


I think I'll look in to the new Avenger truck carb from Holley for my 4.3 Chevy Flat Fender project.

 

[jldiaz]

Pins 27 and 29 of connector C3 (rearmost connector at the PCM) correspond to pins 1 and 6 of the Data Link Connector (OBDII). I had to wire these directly once, bypassing the Harness. It worked.

 

[Kejtar]

The scanner reads "Loss of communication" then "Monitor Mode Exiting".

Call up the manufacturer of the reader. They might give you an idea what to look at (as in under what conditions those codes show up).

 

[Simple Man]

I just sent them an e-mail to see if they had any thoughts on the matter.

By the way, thanks for your help.


Replying to "jldiaz", the only pins that match up on the OBDII port and my scanner are #16 (power) and 5 & 7. I'll try and follow wiring diagrams to hard wire around the harness. No something I'm looking forward to trying.

 

[jldiaz]

Sorry. I double checked the FSM and the SCI pins at the DLC are 6 & 7 (not 1 & 6). These are the ones you need.
The CCD Bus goes in 3 & 11.
4 & 5 are grounds
16 is Battery (+12V)

 

[Simple Man]

The only pins that my scanner uses and the OBDII port on the XJ uses are 5, 7 & 16. 5 is a confirmed working ground. 16 is confirmed 12 volt supply. That leaves pin 7.

I don't have a good enough wiring diagram to be able to trace the wire back to its source to try and hardwire around. The wire is red. I checked twice, the power wire is brown w/ a black strip. Go figure.

Where is the PCM located on a 1998 XJ w/ a 4.0? Sorry but I'm not up on my acronyms. FSM, SCI & DLC?

Thanks


after searching:
FSM - factory shop manual
PCM - powertrain control module
DLC - data control link

SCI or SC-1 still haven't found.

 

[jldiaz]

OK. SCI stands for Serial Communication Interface.
Your PCM is in the engine compartment, at the front left corner. Right behind the left headlight. It has three large connectors: C1, C2 and C3; C1 being the foremost and C3 the last to the rear.
SCI signals travel in both directions: from PCM to scanner (Transmit), it's via pin 27 of C3 through a pink wire to pin 7 of the DLC.
But the scanner has to tell the PCM what it wants, right?
It does that by the receive line from pin 6 of the DLC through a light green wire with a black stripe that goes to pin 29 of C3 at the PCM.
Maybe your AutoXray isn't for Chrysler vehicles? But then, it's not the only scanner that failed. You probably have a loose green/black wire by the SCI connector.

 

[jldiaz]

Rethinking... The transmit line (pin 7 at the DLC) is also labeled ISO 9141K in the manual. If this protocol is bidirectional, you probably don't need pin 6.

In mine, just in case, I rewired 6 & 7.


EDIT: Confirmed: you don't need pin 6 for ISO-9141. The whole SCI confusion came from the FSM. My AutoTap works fine w/ISO.

 

[Simple Man]

I checked for continuity from the connector C3 (pin 27) to the OBDII port (pin 7) and couldn't get it.

My fisrt attempt to bypass it didn't work. I'll try again after lunch. This time more seriously.

I'll post up with results when I get done. I have plans to spend the afternoon with my wife so this might get put off until tomorrow.

Thanks again for sticking with me on this,


Doug

 

[Simple Man]

I did a better job at bypassing the harness with the data line to pin 7. Still dead.

I had been starting the jeep and shutting it off quite a bit. The battery has been a little weak but was getting worse. I did a quick jumper cable start but now it wouldn't stay running. It would run but not idle. I swapped in an Optima from my Willys project. It started great, ran great. And the data line worked.

I disconnected the bypass. I hadn't cut the original data line. The original data line was working fine. A day and a half of getting help online and trouble shooting and all it was just a dying battery.

I should take up stamp collecting!

 

[jldiaz]

Glad you got it fixed.

I think Australia put out a series of stamps with pictures of 4x4s........

 

[Simple Man]

The last chapter....

I went back to get the XJ re-smogged. My scanner was reading it, the MAC scanner was reading it but the smog machine wasn't reading anything from the OBDII port. He sent me to DMV to challenge it. I was told that '98-'99 XJ's had problems with smog machines reading from the OBDII port. His machine at DMV read it fine and I'm now registered for another year.