Help! Electrical issues No bus error

Hi all...been reading all sorts of stuff on the web about this issue and trying to do my best to isolate the cause of the issue.

Wednesday night I started getting an intermittent set of warning lights and bells (most were ABS and airbag related) along with the typical gages fluttering and acting up. Initially this only happened during deceleration. It got progressively worse to the point that when I pulled into a parking lot to try to figure it out, it started to idle rough (exactly like it would do if you turned the key off and back on before it could fully shut down..it "hiccuped" so to speak.).

I got it home with progressively more errors, eventually losing control of my headlights, with the brights stuck on, no turn signals working, etc. After pulling into my shop, I turned the key back on and got the "no bus" error in the odometer.

I've taken a bunch of stuff apart, pulled all fuses, isolated batteries, etc. and can't seem to get the fault to clear. I'm worried it may actually be a bad IPM/FCM that may have shorted internally.

What it is still doing is the following.

• Upon key on, truck goes through normal pre start routine with the lift pump and relays buzzing but no warning lights or bells, and after about 10 seconds the head lights come on full bright, and the "no bus" warning flashes.
• Truck will start and run but will stumble and hiccup
• Removing battery negative results in a spark.
• I've tested the voltage between the negative battery terminal and the negative battery cable...I'm getting 14v or roughly full battery value -> So clear suggestion there is a short to ground somewhere.
• If I remove the IPM power feed, this voltage drops to about 10V.
• I also have 10 V from the negative battery cable to a chassis ground with the IPM disconnect, jumps back up to 14v when I connect the IPM.

So...any thoughts as to where to start with on the short to ground? My gut feel is in the headlights some place (ironically I just replaced the bulbs like for like with Sylvania Silverstars) but want to make sure i don't miss something else.

I replaced the crossover cable last year after some battery failures, and I continue to deal with corrosion, so am planning to replace the rest of the cables.



Thanks!

 

JB,

First, I would disconnect all cables to both batteries to prevent an explosion. Then metodically start inpecting the wiring and cables starting with from the primary batteries and the main battery cables to primary then wiring to the power distribution center, starter relay etc. I'm thinking if you're reading battery from the ground, you're short is with one of the big cables on the battery side of the power distribution center. You can use an ohm meter to check for shorts.

Since you've had corrosion issues, also recommend separating every connector, inspcec, clean, add dielectric grease, and reconnect; remove all grounds, inspect, clean with wire brush, add dielectric grease. Check for shorts along the way with your meter.

Would really be helpful if you have factory service manual with wiring schematics, ground connection locations, and connector locations.

Hope this helps. Please let us know what you find.

Cheers, Ron

 

First question how old are your batteries? Have you checked your ground cables, make sure there clean, use wire brush clean them, then use die-electric grease on those connections.

 

Thanks for the replies. Batteries have been disconnected and only reconnected for troubleshooting, and I'm only using the drivers side battery for that (passenger side stays disconnected). Some more details:

Batteries are < 2 years old. I had been having battery life issues and replaced the passenger side + terminal, the cross over cable, and the connections to the alternator and relays on the passenger side.

So far I've removed, cleaned, and "lubed" the 2 ECM connections, all of the under hood grounds I could find, and all 7 of the connectors on the bottom of the IPM. Last night I systematically removed each connector from the bottom of the IPM to try to see if I could isolate the circuit that was at fault. The only one that made a difference was C1, but that of course has the key switch circuit on it.

So that does seem to point to something in one of the main power cables. I think what I'm going to do then is just order the rest of the set from the Custom Cables guys. I liked the replacements I had.

While I'm waiting on those, any other ground locations to check? I'm thinking about ohming out the head light and taillights?&src=tdr">tail lights since I've had to replace a few bulbs there, but if I had a short to ground that might explain the bulb failures.

Right now I have all of the block grounds disconnected, and the only connection from the drivers negative cable is the chassis ground, and still reading the voltage.

Definitely a head scratcher! Wish I paid a bit more attention in my EE classes in engineering school back in the day. As an ME I know juuuuust enough to be dangerous here.

 

Also, guess I should have mentioned, 2004.5 model w/ Auto Trans if that helps at all. I did find the ground strap from just under the drivers footwell back up towards the bell housing was heavily coated with grease, etc. Cleaned that and seems like for now, no no_bus error...still have voltage though at the battery.

 

So...put everything back together...that might have been the culprit. Truck starts and runs, all works again. No faults, etc. Only thing that doesn't work now is the high beam indicator on the days, but high beams do come on as desired. Time for a test drive.

 

Test drive a success. Still have the service engine soon light on, so will see if I can take that in to be read / cleared. Any other hidden chassis grounds I should check while I'm in there?

 

I had an 03 2500, but cant remember particulars. Fixing grounds and cables will go a long way.

Cheers, Ron

 

There is no such thing as a service engine light on a 04.5

 

There is the engine icon warning light in the top left, which was the only light on after getting it all buttoned up. While it doesn't say "service engine soon" like other warning lights of days gone by, that is what I meant.

I drove it around a bit today and the light turned off on its own. Took it to autozone to have the codes scanned. All of these seem to make sense based on a bad ground and/or the power irregularity I was seeing during trouble shooting.

P1652 - J1850 Communication Bus
P2509 ECM/PCM Power Input Signal Intermittent
P0008 Fuel Rail/System Pressure - Too High
P0882 TCM Power Input Signal Low


So, thanks all for the help, and hopefully this thread will help others with similar issues in the future.

I'll try to post up a picture of the bad ground I found.


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The trucks of today are very reliant on grounds to do things. Most components use 5 volt references and the control side uses the ground instead of switching power on and off.
My own truck had a bad connection in the main battery cable from the right side battery to the left side battery.
This may not seem like a big deal, but the TIPM runs off the battery cable and the alternator was charging the right side battery to 18 volts. While the left side battery had 13.2 volts. If the TIPM is only seeing 13.2, and wants 14.6 it's going to keep engaging the alternator field until it gets it. So yes connections, grounds, green crusties will always create issues on today's trucks. I see it every day because I work on them every day.

 

It sounds like you are on the right path, but please always have both batteries connected as the generator (alternator) is connected to the aux (passenger side) battery and it then charges both batteries (and supplies system power when running) through the crossover cable.

I have also seen crossover cables get corrosion inside them (within the protective coating). Feel the cable a few inches back from the connector and see if it is stiff. It is pretty likely you are due for new cables (not cheap at current copper prices).

Battery diagram for reference (2004 Ram 2500)
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Thanks! I actually replaced the crossover cable last year for that reason. Was going through passenger side batteries annually.

Just recently finished replacing all of my cables a week ago. So far so good! Shout out to the custom battery cable guys for some good replacements!