7 codes J1939 system down
08-28-2020, (Subject: 7 codes J1939 system down ) 
Post: #1
7 codes J1939 system down
2019 pete 567 X15 performance 565 hp factory stock 92,000 mi. Did an EGR tune up about 10,000 mi ago. Today out of nowhere the dash says" increased derate in 4 hours seek service to repair scr, scr system altered or fault detected" the def tank gauge went to empty and it has 7 active codes 6688,4151,3232,2771,3868,4572,4677 all are emission sensor communication problems. So apparently the J1939 network is down i guess? So I looked at what the sensors were reading with insite and the nox sensor says "reading not stable" Then I did some troubleshooting with quickserve trying to isolate which sensor is acting up. Quickserve says to check the engine harness by unplugging the 14 pin crossover connector and then measure resistance at the 3 pin data connector and resistance should be between 108-132 ohms. I did that and it's 120 ohms, ok so the engine harness must be good. Then it says to disconnect the nox sensor and again check resistance at the 3 pin and if resistance is 108-132 ohms you have a bad nox sensor. I did that and again it's 120 ohms. So according to quickserve I have a bad nox sensor, is it possible for a bad nox sensor to cause all this? Also how would unplugging a sensor and getting the same resistance tell you the sensor is bad??


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08-28-2020, (Subject: 7 codes J1939 system down ) 
Post: #2
RE: 7 codes J1939 system down
There is a 120ohm resistor in the OEM harness and another one inside the NOx sensor. They are in parallel, so should read 60ohms when both are good and there is no power in the circuit.

A bad terminating resistor will most definately upset the whole data link. Sometimes you can't even connect to the ECM with Insite while they're playing up.
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 Thanks given by: tree98 , Pd6cas2
08-28-2020, (Subject: 7 codes J1939 system down ) 
Post: #3
RE: 7 codes J1939 system down
Right now it's 120 ohms with the 14 pin connector unplugged and the nox sensor both connected and dis connected. The batteries are disconnected also. I found the terminating resistor in the harness it tests good. Wouldn't the circuit be at 60 ohms if the nox sensor was unplugged or bad?


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08-28-2020, (Subject: 7 codes J1939 system down ) 
Post: #4
RE: 7 codes J1939 system down
If equipped completely remove the ELD connection from the truck and see if the codes go away. Had a similar issue that literally made my truck undriveable, replaced ELD problem solved.
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 Thanks given by: Pd6cas2 , Rawze
08-29-2020, (Subject: 7 codes J1939 system down ) 
Post: #5
RE: 7 codes J1939 system down
(08-28-2020 )tree98 Wrote:  Right now it's 120 ohms with the 14 pin connector unplugged and the nox sensor both connected and dis connected. The batteries are disconnected also. I found the terminating resistor in the harness it tests good. Wouldn't the circuit be at 60 ohms if the nox sensor was unplugged or bad?

Check to see if you have 60-ohms at the J1939 connector for that circuit on the can buss wires with everything plugged in (and power off to everything).

It could also be that you are missing a +5-volt supply wire from the ecm to those circuits.... look in quickserv at the engine wiring harness / ecm wiring diagram and see if the supply line is common to those sensors you are having a failure with.

you could also see if you have roughly about 2.5 volts on each of the can buss lines with power turned on using a volt meter. If one of the J1939 buss lines is +5 volts or 0-volts... something is wrong with one of the devices on it.

last, but not least ... you could start unplugging devices one at a time and resetting codes until you only have one fault code (for the device you unplugged) instead of 6 or 7 at a time.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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 Thanks given by: Signature620 , tree98
08-29-2020, (Subject: 7 codes J1939 system down ) 
Post: #6
RE: 7 codes J1939 system down
(08-28-2020 )marek4792 Wrote:  If equipped completely remove the ELD connection from the truck and see if the codes go away. Had a similar issue that literally made my truck undriveable, replaced ELD problem solved.

Doesn't have an ELD


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08-29-2020, (Subject: 7 codes J1939 system down ) 
Post: #7
RE: 7 codes J1939 system down
Will it let me re set a fault for a device that's unplugged? I would think that would cause an active fault.


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08-29-2020, (Subject: 7 codes J1939 system down ) 
Post: #8
RE: 7 codes J1939 system down
You will get a fault for that particular device but the rest should go inactive if that device is at fault.

Most of these faults can be caused by low voltage being supplied to the aftertreatment system. Make sure you test voltage on these circuits under load.
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 Thanks given by: Rawze , tree98
08-29-2020, (Subject: 7 codes J1939 system down ) 
Post: #9
RE: 7 codes J1939 system down
ok, so after spending needless hours on this yesterday going down quickserve rabbit holes that went nowhere, I had a little clearer head this morning and followed your advice Rawze and Sig and here's what I found.

I looked at the wiring diagram on quickserve and sure enough all these components shared the same 5v supply. A test light confirmed no power to any of the components.I also see there's a 15 amp fuse for that circuit, so after tracing the wiring harness to see which fuse panel it went into I found the fuse and it was blown.

So now I know why there is no power to the circuit just not what blew the fuse, atleast im getting somewhere now !! I didn't have any 15 amp mini fuses so i went to napa and bought a couple packages. Come back and put a new fuse in, turn the key on ...snap... blew it immediately, well that tells me I must have a dead short that's actually good news because that means the problem didn't go away and maybe it's not intermittent and I have a good chance of finding it easier! Next I unplugged all components on that 5v circuit, put a new fuse in and started plugging them back in one at a time and checking the fuse after each one until I got to the outlet NOx sensor and...snap... Found it !!

I wanted to be sure it wasn't a wiring or plug problem before I replaced the sensor so I put a load on the plug with a headlight bulb and checked the voltage it was a little over 12 and the fuse didn't blow with the bulb on so now i'm positive it's the sensor itself. Went to the dealer bought a sensor put it on, hooked up insite all codes inactive, cleared the codes and everything's back to normal !!

So i guess the sensor must have been shorted to ground internally. Thanks for the help guys!!


User's Signature: Warranty??? Yeah right, I am the warranty!!!
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