I replaced the oil pressure sensor and it ran for about an hour fine and now it won’t start and this message comes up. Help please

 

I would check all the fuses and grounds , power wirers . then disconete the battery for a couple min. then try hooking up the battery and see if the bus comes back . the bus is how the computer talks to other parts of the system .

 

When I changed the sensor the back of the plug (not the sensor part) all 3 of the wires were bare copper and probably touched could this have done anything

 

It would be really likely to blow a fuse (if power and earth touched)

If you do not have the FSM, with electrical diagram, to narrow down the search, it is certainly feasible to check both sides of every fuse with a test light in under 20mins

 

I didn't see what year is your Jeep? There should be a data link connector (DLC) port where you would find the bus wire. On mine I think it is the #2 pin wire.

You can use a multimeter to probe and test looking for a normal voltage range value on this bus wire here at the DLC. If it is too high of voltage you follow a certain path unplugging modules one by one until the voltage normalizes. If the reading is too low, or zero voltage, you would follow different pathways for them to see why there is a problem on the bus.

(edited):
Is it possible there are connections or connectors nearby that got knocked out or loosened accidentally?

 

What fuse will this this likely be.

 

Disconnect the oil pressure sensor and see if the No Bus is gone.

 

I have a 2000 jeep cherokee classic

 

I missed that post. Repair those wires, regardless. Exposed wiring will eventually corrode, and cause trouble. If neglected, the wiring will snap right off with the slightest breeze. Been there, done that.

 

With the bus system, those wires are only 5 volts so good clean connections are critical. My thought would be to solder in a new plug. Being a 2000 the dealer should be able to get one, or cut one out of a donor or JY vehicle. My 2000 WJ neutral safety switch plug had broken wires in it and the dealer had one in stock. It must be they are still being used on later models.

I don't think the bus system has fuses. It either communicates or doesn't communicate. If it does short somewhere, the PCM turns it off.

 

I dont even know if it is fused, which is why I suggested checking them all, its about as quick as looking up the FSM, and also shows any other failed fuses

 

There should be no dedicated fuse for the Bus. It could still be worthwhile to look at the fuses just in case maybe something is wrong with them.

The Bus wire is either yellow with a violet tracer, or white with a violet tracer, depending on year and model. The easiest place to access this wire is at the data link connector, which is the connector that the scan tool plugs into for diagnosis (located under the drivers side dash adjacent to the fuse box). The Bus wire is in pin #2 of the data link connector.

You could backprobe and test the wire with a digital voltmeter. See if you find a problem? If you do this be careful not to damage the portion of the terminals that make contact with a scan tool.

I have some copy & paste about it if interested to read:

Set the meter to 'DC Volts'

Connect the red lead of the meter to pin 2 of the data link connector

Connect the black lead of the meter to ground. Any bare metal surface under the dash will work.

Turn the key to 'ON'. Or, start the engine. Sometimes the Bus problem is easier to duplicate with the engine running.

Observe the volt reading on the meter.


If the volt reading is zero, or very close to zero, it is possible that the bus is OPEN, or SHORTED TO GROUND. A different test will be required, which is detailed later in this article.


If the volt reading is close to 12 volts, or battery voltage, the Bus is shorted to voltage, and diagnosis should be fairly easy.


If the volt reading is varying between 0.5 and 2.5 volts, the fault is showing as not present at this time.

Normally what I see on problem vehicles is a reading of 4 to 6 volts. This indicates that a module (one of the vehicle computers) is pulling the bus voltage too high, causing interference and a loss of communication between modules, which leads to the symptoms you are experiencing.


If the PCI Bus voltage reading is consistently above 2.5 volts, we need to determine which module is causing the problem. There is no quick way to do this. Each module on the bus must be unplugged until the voltage returns to the 0.5 to 2.5 and fluctuating range.


Module examples are:


PCM (engine computer)...engine compartment

TCM (transmission computer)...engine compartment

BCM (body computer)...under dash near fuse block

ABS (antilock brake computer)...engine compartment

Instrument cluster

Airbag computer...under center console/armrest

Driver door module (the window switch assembly)...remove door panel to access

Passenger door module (the window switch assembly)...remove door panel to access

Radio

Audio amplifier...under back seat

A/C control head...in dash

Overhead console computer

Immobilizer module...remove steering column covers to access


I begin with the interior modules, unplugging the ones that are easiest to get to. Continue to unplug modules until the bus voltage lowers to a normal level; 0.5 to 2.5 volts and fluctuating up/down randomly. Keep in mind that unplugging some modules will cause other symptoms...try to ignore those for now and focus on the voltage reading.


Once you find a suspect module, reconnect everything else and observe the bus voltage. Reconnect the suspect module and try to duplicate the symptoms. Verify that the suspect module is actually the problem several times before you spend money on a replacement part. Be sure to cycle the ignition key every once in a while during testing. The trick here is to be able to consistently verify that the bus problem is present, then verify that it is not present when the suspect module is unplugged. Try to not let the system 'fool' you.


If the bus voltage is around 12 volts, or is the same as battery voltage, and ALL modules are unplugged, then the bus wiring is shorted to voltage. This problem may not be easy to find. You will have to trace the bus wire extensively. The good news is that this scenario is very unlikely.


If the bus voltage is always near 0 volts, a different method will work.

Disconnect the vehicle battery under the hood.

Connect your meter the same way, but switch to the 'ohms' setting, to check the resistance of the bus. A bus that is shorted to ground will have a very low resistance, possibly below 10 ohms. In a situation where the bus is shorted to ground, a module could be at fault, but more likely the bus wire has rubbed through somewhere and is touching bare metal. Keep in mind that the whole frame and body of the vehicle is ground, so that makes this scenario more likely.


If the ohm reading is 'OL' meaning infinite resistance, then the bus wire is OPEN and must be traced out for continuity. However...if every module is unplugged, and the bus wiring is OK, the meter will display 'OL' for bus resistance.


Read the following information, which is from Chrysler:


Measuring PCI voltage is the first place to go if no communication is possible with any modules. This tells what type of failure has occurred and this dictates the next step. If communication is possible with only one module, an open in the bus is likely.PCI bus vehicle are very easy to diagnose bus problems on. Since each module has a termination resistor of a standard value a measurement of bus resistance (with the battery disconnected) gives a very good idea of the condition of the bus. For example: Termination resistance 350 to 750 ohms would be a normal bus. 0 ohms would indicated a shorted bus OL would indicate an open bus 3300 ohms would be one dominant module only 10800 ohms would be one non-dominant module only

End of copy & paste

The Bus is microvolts being pulsed and sent around between all ECUs so they can communicate. If the PCM is offline.. It may be due to a fault with any of the other 30+ ECUs, or modules.

0.5V - 2.5V and fluctuating is the normal range specified to the Bus.