I was driving home from an evening meeting when I noticed that my Check Engine light was lit.  Now this was not the first time I had seen it illuminate but it was the first time it had done so while driving it in town.  In previous times, it happened while out on the trail and with Lady in some odd ball situation (don’t go there!).  The engine was running just fine and I could not detect any performance issues.  I stopped at the next stop light without so much as a burp from the engine.  I continued home and parked in the garage.  I disconnected the positive cable from the battery and let everything sit for about 15 minutes.  Upon reconnecting the cable, I started the engine and found the light still glowing brightly.  A couple more trips around the area in subsequent days indicated that the light just wasn’t going to go out on its own.  Time to upgrade the tool box!

I had been kicking around the idea of getting an OBDII scanner interface for my laptop PC.  After having finally gotten around to installing my Panasonic Toughbook last fall, I already had the expensive part of the project in the TJ.  It seemed like a good idea to get the scanner interface now.  My ’98 TJ wasn’t getting any younger and eventually other things would cause the Check Engine light to come on. 

I started searching on line for ODBII interfaces and PC software.  After looking through various web sites and reading their information, I ended up getting the BR-3 interface from obddiagnostics.com  This unit attaches to your PC via a 9 pin serial cable which comes attached to the interface box.  The cable is about 6′ long.  The other end of the interface box has a 2′ long cable that has the OBDII connector on it.  Software for the interface can be downloaded from the web site.  Versions for both Windows and DOS as well as Linux are available, although it appears that the Linux version is not directly supported by the interface manufacturer..  The price was $98 delivered to my door via USPS Priority Mail.  The interface is also available in kit form and more info about it can be obtained on the web site.

Here is the business end of your Jeep that the OBDII cable will attach to.  On my ’98 TJ, the connector is located in the vicinity of your left knew, right underneath the dash. 

With the cable connected to the ODBII port, connect the 9 pin serial cable to your laptop and you are ready to go.  While it works without any issue, I was not overly impressed with the method by which the connector was attached to the cable.  I am not quite sure how it was done but some of it is held together with tape.  The occasional use I will give this unit will probably have little impact on the connector.  If the intended purpose for this unit was to see daily service, plugging and unplugging it, I am not certain what the long term results would be.  For all I know, it will last forever….it’s just that it leaves me wondering if it really would.


As the manufacturer’s web site states:

“With the interface attached and the software running, it allows you to Read out trouble codes when your “check engine” light comes on. You can also clear these codes. You can retrieve pretty much any piece of OBDII mandated diagnostic data from your vehicle. The interface supports OBDII protocols commonly used in US vehicles: VPW (General Motors), PWM (Ford), and ISO9141 (Chrysler, Asian, and European), and ISO 14230 protocol (also called Keyword 2000).”

So back to the Check Engine light I had gotten previously……with the software loaded onto my Toughbook, I attached the interface cables.  I selected the appropriate vehicle interface from the menu (use ISO9141 for your Jeep).  From there, it was basically pointing and clicking as I snooped around the software screens.  I checked the trouble code and with some help from my FSM and the internet, determined that the problem seemed to be the downstream O2 sensor.  I was getting a flat line for that sensor instead of the more sine wave display that is typical for the O2 sensors.  In fact, the upstream sensor looked great and according to what I could decipher from the FSM, the downstream sensor would look similar but with less fluctuations in its display (assuming the catalytic converter is doing its job). 

Saturday morning came and I once again plugged in the interface and fired up the Toughbook to have one more look see before I headed off to the auto parts store to obtain a new sensor.  Yep….same display as before (so much for the O2 fairy coming by in the middle of the night to fix the sensor!). 

As I won’t trust the person behind the parts counter unless I absolutely positively have to, I decided it would be best to show up at the counter with sensor in hand….at least I would have a chance to compare the new sensor to its dead cousin before handing over my dollars.  I slid under the TJ with a couple of wrenches to remove the sensor.  OOPS!  I couldn’t believe my eyes…..I was getting ready to put a wrench on the sensor and unscrew it from the exhaust pipe when I noticed a little shiny spot of copper color on the wiring harness.  Sure enough….a closer examination revealed that the sensor’s wiring pigtail had come in contact with the back side of the t-case’s rear output yoke.  The rotating yoke had barely nicked the wire enough to cut it…and I do mean barely because the insulation was still holding the wire together although there was a clear break in the copper wire.

It didn’t take too longer after finding the problem before the soldering iron and some heat shrink tubing was used to patch things up.  I put some sensor safe anti-seize compound on the sensor’s threads and screwed it back into the exhaust pipe.  The wiring harness connector was attached and I was ready to give it another test. 

Good news….the sensor display indicated my downstream sensor was alive and apparently doing well.  It was no longer flat lining as it had been.  It’s display pattern followed that of the upstream sensor but at a reduced amplitude (which the FSM says is normal operation). 

OK….so I was pretty happy about the entire outcome.  Granted, I would have found the broken wire eventually but I am not sure how long it would have taken me to get around to pulling out that sensor.  Yes, I could have gone to AutoZone or some such place and had them read the code for me….and that certainly would have gotten me headed off into the right direction.  But now that I’ve had a chance to use the OBDII interface software, I really like the ability to look at the vehicle data in live time to see what it is doing.  Yes, you can actually leave the interface connected and drive around while monitoring various engine parameters.  As I mentioned earlier, with the Toughbook laptop now mounted in the cab, it is just makes sense to have the OBDII interface and software as yet another tool for the Jeep.