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No bus wont start NOT CPS

U

umkills

NAXJA Forum User
Location
kentucky
ok so i have a 1999 jeep Cherokee classic 4.0 4x4, she ran before, but there was always a spot on the pedal that she would act like she wasn't getting gas...the passing gear cable was frayed so i changed that cable out, after doing so she would not start, i get a no bus code on the odometer display, my abs relay hums like a sob, when i turn the key. and the CPS is fine it reads just like it should on the volt meter, and the shops computer wont connect to to it, and this is a snap-on 15k computer, not ur cheap everyday personal ones, i need serious help guys....i don't think i missed anything, but please give me ur input
 
disconnect all 3-wire sensors. I'd suspect one has shorted the 5v reference.

CPS
CMP
MAP
TPS

And lastly, the clockspring in the steering wheel.

then turn the key on and see if you get a response.
make sure to check all fuses in the PDC and fuse center with a test light.
 
unhooked all three connectors to the ECM upon doing so i noticed on my C2 connector a pin has broken.....where the hell can i find just an ECM C2 connector, does anyone know?
 
Replaced the c2 plug going into the ECM, still getting the "no bus" and she still wont start, anything else u guys can think of, i feel like im running outta options and its getting very disheartening....any help would b greatly appreciated thanks
 
i just realized i read the first reply to this wrong, im gonna go unhook all 3 wire plugs and see what happens, will 4 sure let u guys know something
 
ok, so i tried unhooking all 3 wire plugs, i done them individually each time turn the key and each time getting the "no bus" code on the odometer....i never thought id have such a time changing the passing gear cable...after doing so is when this problem started to occur...so yeah any help from u guys that are smarter than i am about these jeep cherokees would really help...hope to hear something from some one thanks in advance
 
it's not just those sensors listed.

I've had an oil pressure sender cause no bus.

Any 5V reference sensor can cause it.
Start disconnecting EVERYHTING engine management related one by one, turn the key to the on position, when the fuel gauge works you've found the culprit.

Speaking of, it can also be the fuel level sender ;)
that's my process for finding no bus issues. The ECM is going into fail safe and shuttig down, the dash is telling you that the can bus is down.
 
ok, so unhook every plug i can find on the thing, one by one, let me ask this, am i unplugging then checking for the no bus code, then hooking it back up before i goto the next, or do i just need to leave them unplugged after turning the key and going onto the next one?
 
OP,

I think you should get that Snap-On tool connected so you can see what code(s) are stored.

Refer to the DLC pin out below.

You need 12 volts at pin cavity 16 and ground continuity at pin cavs 3 and 4.

If you don't get 12 volts at pin cav 16, using 3 and/or 4 as the meter ground, put the meter ground probe at the gas pedal bracket stud nuts (see pic). If you get 12 volts now there's a possibility that the DLC ground (G102) wires were nocked off when you changed the kick down cable. (see pic)

If you still don't get 12 volts check the DLC fuse. The fuse for the DLC pin cav 16 is in the PDC (see pic).

DLC.jpg


Gas%20Pedal%20-%20Copy%202.jpg


G102 Location:

G102%20DLC%20Ground.jpg

.
PDC "DLC/Head Lamp Switch".

%2098%2099%20PDC%20REV%2012_06_2015.jpg


See if you can get that Snap-On tool fied up nd get some codes.
 
umkills said:
ok, so unhook every plug i can find on the thing, one by one, let me ask this, am i unplugging then checking for the no bus code, then hooking it back up before i goto the next, or do i just need to leave them unplugged after turning the key and going onto the next one?
Click to expand...

you can leave the previous ones disconnected.

The suggestion about checking for voltage at the DLC is good, but even if you have it if the ECM is in a failsafe state you will not have communication.

When it fail safes it shuts itself off to prevent damage from a short.
 
alright so heres the situation....i have everything i know of unhooked from the motor and the transmission and the gas tank....im still getting the no bus code.....if my c2 connector that broke on me caused the computer to go into safe mode, since i have the c2 plug replaced, shouldnt the computer be able to talk to it again, maybe its stuck in safemode or some crap.

i checked the dlc voltage, it read 12v and my dlc ground was still connected, i unhooked it and checked it out and rehooked it back up, still no bus.....im about to sell the damn thing....is there anything inside the transmission, when u take the pan off that could cause this problem? maybe i hit something changing the passing gear cable?
 
what senders have you disconnected?

it's possible that the broken c2 connector shorted and the PCM is cooked, but unlikely.
 
umkills said:
alright so heres the situation....i have everything i know of unhooked from the motor and the transmission and the gas tank....im still getting the no bus code.....if my c2 connector that broke on me caused the computer to go into safe mode, since i have the c2 plug replaced, shouldnt the computer be able to talk to it again, maybe its stuck in safemode or some crap.

i checked the dlc voltage, it read 12v and my dlc ground was still connected, i unhooked it and checked it out and rehooked it back up, still no bus.....im about to sell the damn thing....is there anything inside the transmission, when u take the pan off that could cause this problem? maybe i hit something changing the passing gear cable?
Click to expand...

Can your Snap-On tool connect now?

Hook all disconnected sensors back up and clear the codes.

You can check the status of the CCD Bus without the scan tool.

Go back to the DLC/Modules schematic in post #12.

Disconnect the battery negative post connector.

Set your [digital] Ohmmeter to 200 Ohms.

At the DLC, touch pin cavities 3 and 11 with the meter probes. You should see 60 Ohms. If you see 120 Ohms, either the Termination Module in the PCM or in the Instrument Cluster is bad, or the CCD Bus wiring to these modules may be open.

The Instrument Cluster has the Bias Module that generates the 5 volts used on the CCD Bus - the Termination Resistors are supposed to drop this voltage down to 2.5 (+/-).

If you are getting 60 Ohms, check the bus voltages,

Using a voltmeter set to 20 VDC, touch pin cav 3 (+) probe and pin cav 4 and/or 5 with the meter negative probe. You should see around 2.5 volts.

Repeat this but touching pin cav 11 (+). Again, 2.5 volts.

See the voltage limits on the schematic.
 
umkills said:
and i have the codes it had before the computer unable to connect to it, i wrote them all down
Click to expand...

Are you talking about the scan tool can't connect, or it can't communicate - big difference.

Look at the DLC schematic again. Note that these are two ports for the Serial Communication Interface. This is how the scan tool 'communicates'. The PCM has it and so does the TCM. The only two modules that do.

If you think the wiring at/to the transmission got dicked up some how, reconnect all sensors and clear any codes.

Disconnect the TCM and see if that gets rid of the NO BUS.

If it does, there's a chance certain inputs to the TCM have been disturbed and it is corrupting the CCD Bus.

I have a procedure for checking the TCM inputs but I'm not going to post it until you get back.
 
alright, im gonna try all these idea's tomorrow, its getting dark this evening, and i wont be able to see shit. also, i have to get my brother in law to bring the snapon computer home tomorrow, he owns a garage. but out side of the computer, he refuses to help me...go figure...but all this i will try and get done tomorrow. thanks guys ill get ya posted asap
 
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