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Dodgerench
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3385
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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2000 Dodge Ram2500 Van Cargo, automatic, 5.2 no bus

Customer Question

2000 Dodge Ram2500 Van Cargo, automatic, 5.2
no bus displayed in odometer
check engine light does not light (not even during gauges check)
scan tool shows no trouble codes
no codes shown during cluster check (hold the trip button and turn key)
brake and abs lights come on, o/d off and trans temp lights come on
(all soon after starting to drive. If hot start o/d and trans temp are on and never shut off, if cold start they will come on after a few minutes.
I just bought the van yesterday and was aware that it had some issues, It drives fine with the exception of a quick jerk to the left when braking hard and it feels like its not going into overdrive at highway speed. (didn't notice those till i was on my way home) My initial though was a wheel speed sensor was causing the brake lights and that a trans temp sensor malfunction was causing the o/d and trans lights (it's only warm to the touch when they come on) but I have no idea why there are no trouble codes and i am clueless as far as the no bus message.
Submitted: 1 year ago.
Category: Dodge
Expert:  Dodgerench replied 1 year ago.

Hi, welcome to JustAnswer!. This is Ed.

I'm afraid it's bad news. It sounds like your PCM (engine controller) isn't awake. a NO BUS message, along with refusal to run, means but just one thing -- that the PCM isn't sending information to the instrument cluster (on the bus network) because it's unconscious or dead.

Try this.

First, locate the PCM, which will be screwed to the bulkhead right above the radiator fan area, using three 5/16" fasteners. It's the metal module with three connectors.

PCMs in our truck line are somewhat sensitive to temperature when they act up. If they die out on you (and prompt the NO BUS message), it's usually tied to normal underhood temperatures that heat the controller to the point where whatever was weak... just fails. It's been sitting for a bit now, so it may just start on its own. If not, you can try dousing the PCM in ice water or packing ice around it to see if it comes around quicker and removing the three screws to allow access to the back side of the unit may speed things up.

Another thing that's become more common lately would be a circuit board break. Wiggling any of the three connectors (particularly the far-right one) with the key on may cause a clicking sound in your underhood fuse and relay panel, the PDC. That's because the very first thing a PCM does when it wakes up is to fire the ASD and fuel pump relays, which will account for the noise. At that point, the engine is likely to start, but it's not going to run far or long, so don't trust it. You'll be needing a new PCM.

Other things can cause your PCM failure, but try these two suggestions first. There is but one external issue that can cause a PCM to fail, but they won't come back. If you can get your PCM to wake up even briefly, the problem is right there with the PCM itself. On the other hand, if it won't wake up no matter what, we'll need to press on. Let me know.

Ed

Customer: replied 1 year ago.
i never said it doesn't start
Expert:  Dodgerench replied 1 year ago.

You're right, I read something into your description that didn't exist. Sorry... let's try again, starting with the NO BUS message. If we can find the reason for apparent loss of communication at the cluster, we might solve some of these other problems at the same time.

NO BUS in this case probably means just that -- the cluster isn't getting a PCM message, but it may be that the whole bus is down. This model year uses the 2-wire Chrysler CCD bus network, which consists of two separate data circuits, both of which operate on a 2.5 volt bias. Let's begin at the Data Link Connector, which is the handiest place to measure CCD voltage. That's the same connector you use for your scanner.

You'll need a digital voltmeter for this, because analog meters don't have the internal circuit impedance to read sensitive circuits of this sort. Set your meter to 20 volts DC, find a good ground source. We'll be testing the third terminal from the left in each row on the DLC with the key on.

A good CCD circuit should show a voltage between 2.4 and 2.6 volts, with the digits to the right of the decimal "dancing"... changing rapidly... as data streams past. Any voltage above or below these thresholds will spell trouble, as will the lack of rapid change in the tenths and hundredths column of your multimeter.

I don't know what to make of the complete lack of a MIL illumination at key-on or during your cluster self test. CCD messages are used to turn the MIL on (as requested by PCM), but the default is normally to have the MIL ON if no signal is given. It's very likely that you just have a bulb outage since pretty much everything else lights up, but we'll see.

I think you said that your ABS light is on and if so, does your speedometer work? The vehicle speed reading is taken from ABS, transferred to the PCM, converted to a VSS and then shot over the CCD bus to the cluster, so if you have speedo, it means CCD outage isn't universal.

Talk shortly,

Ed

Customer: replied 1 year ago.
I did the voltage test and on both terminals it is 2.4x with x changing between 4 and 5 every few seconds Speedometer works and so do all other needle gauges.I tried unplugging the wiring connector from the transmission and got no trans temp or O/D light but only 2nd and 3rd gear worked now, no bus stayed on.I went online to look for a used PCM, the bold number on mine is 111AD, it appears this belongs to a 5.2L 1999 dakota, could someone have already replaced it with the incorrect part or did that one go in both vehicles? I swapped it with the one from my '97 van that I've had for a while and works great, and it started right up but this time no working gauges and no bus was still there, this time it flashed the mileage 4 times before going to 'no bus', im assuming there was no CCD in '97. It drove the same, ABS and Brake both came on after about 3 minutes which is the same thing that happened before, and also I only get gears 1-3, no OD even though the OD and Trans Temp lights were off now.When I put the PCM from the '00 in the '97 it also started up fine but now the O/D light was on in that one.
Expert:  Dodgerench replied 1 year ago.

You're right about the 97 PCM and CCD, it didn't come on board until 98, so your gauges don't have a chance with the older controller.

What's really bothering me is that your cluster has a working speedometer, yet the odometer window show NO BUS. That isn't possible, because the vehicle speed signal begins as an ABS wheel (or axle) speed value, which is bussed to the PCM (via CCD), then converted to something the PCM understands and output to the cluster... also on the CCD. The CCD bus has to be present and active to get the amount of function you do have, so something is apparently broken. It could be the PCM or it could be the cluster, but I think those are your only two choices. If given the opportunity, I'd reach over and grab the factory DRB-3 scan tool to monitor both systems for what they see in their inputs-outputs screens. I honestly don't know what to tell you at this point because we've run into an impasse with lack of information.

I'm going to opt out of your question to open it to the rest of the JA expert community. I'm going to be gone for a few days, so if by then nobody has picked your case up, we'll continue. There is no need to rate at this point and if you'd rather not wait, contact customer service for a refund, which they will happily process.

Best of luck,

Ed

Customer: replied 1 year ago.
Thanks for your help! I hate throwing parts at vehicles to find a fix so hopefully someone can point me in the right direction!-Justin
Customer: replied 1 year ago.
check engine light update: I replaced the bulb, now it works, but after holding the trip button and turning on the key to do the cluster check, and then after the check if going immediately to crank, it will remain on with the trans temp and o/d lights!! scan tool said commanded off!?? And if just turning the key to on without doing that cluster check it will never illuminate.

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