NO BUS code

Does anyone know what "no bus" on the odometer means? The starter isn't cranking, solenoids not activating, but the ignition switch relay is clicking. Just trying to get my rig back together. I've checked my leads a couple times but I'll go check them again.

You mention that you are trying to get your rig back together.... What recent work has been done to it that may be related to the NO BUS? More details might be helpful. Something has happened to the computer bus, you may want to concentrate on all PCM and relay box related connnections to start with, especially if you've had them apart.

Disconnect your crank sensor and see if the "NO BUS" goes away. If it does, replace your crank sensor.

CPS CPS!!!!!! ask me how i know:gonnablow they go out - i hsd the same thing happe on the trail about 4 months ago

birchlakeXJ said:

You mention that you are trying to get your rig back together.... What recent work has been done to it that may be related to the NO BUS? More details might be helpful. Something has happened to the computer bus, you may want to concentrate on all PCM and relay box related connnections to start with, especially if you've had them apart.

Click to expand...

Swapped one cherokee's guts to another. Lots of work. :explosion I just didn't know what the "no bus" code could mean. I went connector to connector tonight and double checked all terminals. If I cross the terminal leads on the solenoid to crank it then it cranks great. But not with the key. And I still hear the starter relay switching when I hit the key. So I'm sure it's something obvious that I'm missing. There isn't much else in the circuit.

I'll also check the CPS. It may have gotten damaged during the engine swap.

I would agree that the CPS is definitely suspect in a no-bus / no-start situation but when the CPS shorts, wouldn't it still allow the engine to turn over but not fire? I'd concentrate on the cranking problem and when you have that fixed, the no-bus will hopefully be gone!

That's what I was thinking. I'll check it out again tonight.

The temporary solution for this is to disconnect the battery, remove the instrument cluster and clean all the pins and connectors of the little black spots and then reinstall. There is a TSB addressing this issue....
On my 98 the NO BUS displays on the Odometer when the signal from the bus connectors behind the cluster lose their connection to the cluster due to oxidation on the pins. The guages go dead, the Air Bag light illuminates and the Check Engine light illuminates.....
I've had the instrument cluster out almost a dozen times for this same issue including a trip to the dealership about 8 years ago where they cut the old bus connectors off and soldered new ones in. The problem resurfaces again...
What now works for me to restore the instrument cluster function is to take the directional arm and flip it up to make a right turn... The function of the cluster returns...

Well all my gauges are working good so I wouldn't think that is it. Possible though. I'm going to guess I have a ground issue or a connection loose somewhere. I verified that the starter relay is clicking when I turn the key to start, and the fuel pump relay is clicking when the key is turned on. So it sounds like the problem isn't on the control side but rather on the power to the solenoid side. I finally got a multimeter today and I'm going to shoot some wires and see where the voltage stops. Hopefully this will work. I'm still thinking I'm having some grounding issues. Next step will be to add some more grounds. Thanks for the responses.

Could be the ignition switch causing the cranking issue. You might want to check that out, too. Did you swap columns?

Turns out it was a loose connection. With the wife in the Jeep and me disconnecting, cleaning, and connecting each connector I found the bad connection. I figured it wasn't in the relay system since the relays were both working. Though now I still get the no bus code which makes me think that it still might have a bad CPS or something. Who knows though. Like I said this entire Jeep has new guts. No wire left behind program. Updating the interior and everything. Almost there now. :repair: Just got to get it running. :laugh:

Making progress; that's good news! And now that it cranks over and you still have the no bus / no start, I would concentrate on the crankshaft position sensor and of course that entire associated circuit (wiring/connectors, etc)

When the crank sensor shorts out, it (temporarily) pulls down the power supply at the computer resulting in a NO BUS and of course a no start. I do think that other sensors can pull down the bus as well but from what I've seen, the crank sensor is the most common. IMHO, the crank sensor is the most common sensor failure on the XJ. You said that you did a wholesale swap from one XJ to another. Do you have a spare CPS from the swap vehicle to use in troubleshooting?

Brainstorming here; somethign you could try if you wanted to. Verify with a meter that the 5v supply on the computer is pulled down. Then start unplugging 5v sensor connectors one at a time (start with the CPS) and when the short disappears, that is the suspect sensor/circuit to concentrate on. I used that technique once on a buddy's vehicle. If you can't find a problem with any of the 5v sensors/circuits, it is possible that the computer could be bad as well I suppose but I'd suspect a sensor/circuit first.

Good luck and keep us posted.....

I agree that it is probably a sensor/circuit. I'm not leaning toward a bad computer. I still haven't had a chance to mess with it. I'm also thinking the fuel pump isn't running. The fuel pump will pump if CPS is not working, right?

coastie124 said:

The fuel pump will pump if CPS is not working, right?

Click to expand...

it depends on how the cps fails.
no, the fuel pump will not always pump, the cps takes out the asd relay which controls the spark and the fuel pump relay.

The 98 and up run a PCI system.

Everything communicates with everything else through digital signals, not just voltages.

A bad connection in any one circuit will cause a "NO BUS" on the dash.

In our case it turned out to be the Sentry Key System.
The Connector to the unit around the ignition key was bad.

Since your jeep is a 98' you don't have to worry about that at least.
The Sentry system came out in 99'.

We were able to get the jeep to run some times with NO BUS but the dash was dead and it would only do that if it was running while the connection break occurred.

Once NO BUS is detected, the jeep will not start. no matter what the problem is.

Its a connector someplace. I have had the Dash out of our 99' because of the reports here about the pins corroding. I believe that helped as well.

I have noticed the power seats and the windows are not included on the systems BUS. I would think the only thing you DON'T need to check would be the seats, windows, headlights, under hood light, and anything that is not connected in to the computer.

Hope this helps.
Its a VERY annoying problem.



XJR

Thanks for the help! It is a 99 xj btw. I still have some things that I haven't connected yet because I didn't need them yet. I haven't hooked up the headlight harness, the ac system isn't installed yet and there are a couple of other little items. I guess I'll just have to finish the install before I can get it started. The fuel pump relay is working but the pump isn't pumping. I have a feeling I've got a lot of kinks to work out. Hopefully it'll be running soon!!!

On a side note does anyone know where I can get an emissions evaporation canister for a 99 xj?

Turns out it was just a ground as I expected. It's running now. Idles good. I still have to service the tranny, transfer case, install driveshafts, and exhaust. I hope to have it running down the road tomorrow evening. Now I can concentrate on the interior and working out the kinks.