Dead Diagnostic Port

[Scotty Hutto]

My 2006 Diplomat has a J1939 (9-pin) diagnostic port in the engine bay, a J1708 (6-pin) port in the front run bay, and a J1708 (6-pin) engine diagnostic port next to the steering column. 

The first two work fine, but the J1708 port next to the steering column does not have power (checked with multimeter). I have no idea if the data connections are good, since nothing wakes up without power. 

I’ve checked every fuse I can think of, and (attempted) to trace the wiring to find a bad connection or blown fuse, to no avail.  

Anyone have any ideas where to look next?

I’ve purchased a Bluefire and it works great on the J1939 engine diagnostic port in the engine bay, but unfortunately the low-energy Bluetooth transmitter can’t reach the front of the coach…

Thanks,
Scotty

[Ivan K]

This is not going to help you much with fuse location but my pin C is getting permanent full voltage from a fuse in FRB,  marked diagnostics. It is always hot as long as the battery is ON. In desperation, I would hook it up to any 12V source nearby. If you wanted to confirm that the data link is wired, pins A-B should show low voltage between them and you might see a very slight continuous variation in that voltage if your meter can react to it.

[jacwjames]

In my passenger side rear electrical bay I have 3 fuse holders that hold 2 fuses each.  A total of 7 fuses in these holders most of them are for the engine and at least one is marked diagnostic.  No idea of any of these fuses supply power to the front diagnostic port. 

[MyronTruex]

My buddy was installing a (???? engine monitor device), and finding the one port next to the driver did not work properly we dug around and found a second one in the area next to the driver or the outside compartment that did work.

I never gave it any real thought after that. 

We did not chase it with a voltmeter. 

He is on here and may respond. 

[pulsarjab]

On my 2000 Diplomat, there is a port next to the steering column that did not work when plugging in an engine monitor. Found another port inside the driver side panel that did work. Plugged in the monitor and it has worked great for five years.

[Bill R]

@Scotty HuttoWhen I took my 2006 Windsor to Cummins so they could download my ECM data using the Insite software, they tried first to connect to the diagnostic port by the steering wheel.  They were not able to read anything, so they switched to the diagnostic port in the engine bay and was able to connect to the ECM there.   I didn't think anything about it at the time, but now I am wondering if I have the same issue.  I am going to check the voltage on mine by the steering column and will let you know what I find.

[MyronTruex]

Thanks for responding Greg. pulsarjab that is. 

I couldn't remember exactly where that port was. Seems strange the one under the dash does not work and appears to be a common issue. 

[Scotty Hutto]

Solved:  The 7.5a DIAG fuse was blown.  All working now…

[jacwjames]

Where was the fuse located??

Mine is in the rear passenger side electrical bay.

[Scotty Hutto]

Rear passenger side battery compartment (which serves as the rear electrical bay on my coach). 

Up high on the right wall of the batter compartment. Three two-fuse fuse holders tucked in upper right corner.  Lettering had come off the labels, so it took some poking around.

I’ll take pictures in case anyone else with a Dip or Knight needs to find them. 

[jacwjames]

Mine is basically the same general location.  They are shown in the wiring diagram.  In my case I have 3 fuse holders with 7 fuses.   This is the 3rd or 4th time in the last ~6 months that someone has had a fuse issue.  

Glad you found it.