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This is about my daughters 2000 Jeep Grand Cherokee Laredo V8 and the many computers and sensors within the vehicle.
She has replaced the main compiuter with a new computer and had the computer flashed at Chrysler.
After this several sub computers, BCM, TCM, PCM, Etc. have been replaced. Also replaced are several sensors in the vehicle. Most of the replaced computers and sensors were new but 1 or two was from another vehicle a Dodge Ram Truck Body Control Module to be specific. After speaking with a mechanic they are saying these sub computers are VIN number specific and that after initial programming they can not be programmed to a vehicle with another VIN number. DOES THIS SOUND RIGHT?
Are some of the sensors also VIN number specific?
Other than take the vehicle in to a Jeep dealer for diagnostics are there any other recommendations for my daughter to follow? Dealers are very expensive as we all know.
Some of the probelms the truck is having are;
1. key light comes on solid lit while vehicle is running but is also intermittant.
2. Vehicle stalls when key light comes on, also intermittant.
3. Around 30 to 40 MPH vehicle starts heavy vibration and shaking of stearing wheel also described as as driving on a very rough and rocky road feeling. This does not happen every time the truck is driven, sometimes it takes over 45 mintes for this to occur. As far as I can tell the Jeep is going into limp mode after this happens and the car must cool or sit unstarted for a while before it will return to normal conditions.
4. Vehicle has MIL code P1698 TCM “NO TRANSMISSION BUSS MESSAGE”, after reseting the MIL the c ode comes back within minutes.Over $1500.00 has been spent for repairs and the problems remain. Some mechanics are suggesting a wireing issue (I tend to agree this is a real possibility) but could this also be a problem with computers and sensors from a different VIN vehicle? It is my understanding that the PCM is also suspect when this problem occurs.
Note this truck has only had the main computer flashed, all other sub computers and sensors changed have never been updated by flashing.
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First off, are these the same symptoms that prompted all of these parts to be replaced, or has the problem changed since all of this work started? I have seen 4.7 WJs act up from a bad crank sensor, although the symptoms are usually different, after all you’ve been through it wouldn’t be a bad idea to look into. To answer your specific question – some of the modules are “VIN programmed” to communicate with each other, but most aren’t. I couldn’t tell you 100%, but I believe only the PCM, TCM, SKIM (anti theft immobilizer) and instrument cluster are “VIN programmed.” I believe other modules and definitely all sensors can be swapped out with no issues, although the BCM may need to be configured by the dealer if it’s not exactly the same.
Because of the intermittent nature of the electrical problems, I would say it is a short in the PCI bus circuit. This bus is used to allow all the modules to communicate with each other. Although your symptoms are not “textbook” PCI communication symptoms. You asked about my 04, which actually did have a PCI communication problem at one point, but the symptoms were more like the ones listed below. A new passenger door module was the remedy for mine, which I diagnosed using the procedure below. The key symbol on the dash and fuel cut off are part of the anti theft immobilizer system, there is an antenna in the steering column that detects if the key being used matches its security protocols. If the communication to this system is interrupted, the main computer cuts power to the fuel injectors to prevent the vehicle from being driven. The TCM code you mentioned is also related to PCI bus communication. I’ve copied some diagnostic info about the PCI bus below. But basically the idea is to check the voltage on the PCI wire, and unplug modules from the circuit until a change in voltage is noticed. If all modules are unplugged and there is still an erratic voltage reading, you’ll have to begin hunting down a short in the wire.
“The PCI Bus system is a one-wire communication system. It allows the various modules (computers) on the vehicle to communicate with each other and share information. This information sharing reduces wiring complexity.
The PCI 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. On LHD North American Jeeps, the data link connector is located under the driver side of the dash, adjacent to the fuse block. It is easily visible without removing any panels.
The PCI Bus wire is in pin #2 of the data link connector. Normally I remove the connector from it’s bracket and pull it down for better access. This allows me to backprobe the connector with my voltmeter. You do not want to damage the portion of the terminals which make contact with the scan tool connector.
Here are the symptoms you are probably experiencing with a PCI Bus issue:
The A/C blows normal volume but the air is not cold, because the compressor will not engage, even with the ‘snowflake’ or ‘A/C’ button pressed.
The instrument cluster backlighting is ON at all times (when the key is on), even with the headlamps OFF.
Power windows are inoperative.
The overhead console displays ‘lines’ instead of information.
The gauges are not reading correctly.
These symptoms may come and go. Often PCI bus problems are intermittent.
The PCI Bus system operates on a 0 to 7.5 volt square wave. If you were to connect an oscilloscope to pin 2 of the data link connector, on a system with no problems, the oscilloscope would display a nice square wave. Most people do not have a $2000 scope, so I have devised an easier method. You will need a digital voltmeter to continue.
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 PCI 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 PCI 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 PCI 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 not present at this time. Verify this by inspecting the operation of the windows and other symptoms.
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.”
stiv625, spoke to my daughter and she advised all of the repairs have been chasing the same problem, CAR STALLING ON ROAD.
Thank you for all the info, I am extremly tired now but wll get back to you after a little rest. We may be on the right track with this. 🙂
Monty
I hope not, but we may be at a point of no return with this Jeep. Unfortunately after all the money spent on repairs, with no relief from the problem, my daughter has had to drive the Jeep a few times knowing it is not ready to drive. This was unavoidable for her as the families other car also is having trouble.
Tonight there was a smell like something getting hot or burning and the shaking rough ride returned. When the Jeep was pulled off the road, trying to remove the key from the ignition, the gear shift would not move. After a few minutes the shifter it eventually allowed removal of the key. Now it has been towed to home with a frustrated owner who seems ready to throw the car away for junk for a few bucks to anyone who will tow it.
Too bad, this vehicle was in really nice condition inside and out, it even drove nicely until the problem started again. With it shutting down and now maybe a trashed transmisson to boot I wonder how much she can get for scrap steel or a salvedge yard parts car? The motor seems to be solid with plenty of power to spare based on the last time I drove it a few days ago.
If I thought there was a chance of saving this Jeep I would quickly chance $100.00 for it. Even at my retirement age I think I could eventually electrically diagnose the P1698 MIL code and repair that. Fixing a damaged transmission is another thing, I could not take that on without help from a couple of strong boys
I will return if she changes her mind about getting rid of the Jeep and can prove the transmission is not damaged. Only waiting for the Jeep to cool and taking a short drive will give us an idea if it is saveable or tell us if it is really junk ready.
Sorry to see this outcome, too bad the only option my daughter had was to drive the Jeep anyway potentially causing more damage.
MAYBE I POSTED TOO SOON! I just recevied a call, my daughters husband went to get the car instead of having it towed a short distance home. It had cooled down by the time he arrived to drive it and drove perfectly the rest of the way to their house. Maybe there is still hope for this Jeep with a hopefully small electrical short between or around the TCM / PCM and buss message wireing.
[quote=”stiv625″ post=133247]
Here are the symptoms you are probably experiencing with a PCI Bus issue:The A/C blows normal volume but the air is not cold, because the compressor will not engage, even with the ‘snowflake’ or ‘A/C’ button pressed.
The instrument cluster backlighting is ON at all times (when the key is on), even with the headlamps OFF.
Power windows are inoperative.
The overhead console displays ‘lines’ instead of information.
The gauges are not reading correctly.
These symptoms may come and go. Often PCI bus problems are intermittent.
“[/quote]None of these probelms are present to my knowledge. I have speciffically ask about the above items since I have not been driving the car when it had the problem revealing itself. As for the A/C, it has been disconnected we think it needs freon, that will wait until we see it the car is otherwise repairable. Do you think the PCI Bus wireing could still be the problem and should we look at the same things you suggested or only part of them since everything else is working?
As I write this I thought maybe the A/C is ok but showing the symptom you described. In this case that would be a good thing since the A/C problems may go away after finding the PCI Bus troubles. I’ve got my fingers crossed on this one. I bet the A/C never had gauges on it and everyone assumed it was low on freon. That’s my next question for my daughter.
EDIT: I like you have seen this write up in several places online. I wish I knew who originally wrote and posted the info. They might be able to guide me a bit farther since most of the symptoms do not exist on the Jeep being worked on. The hard shaking of the vehicle, running OK when engine is cool, and recent locking up of the shift lever all seem to point to the transmission not working correctly. Maybe it is in the area of the TCM or between it and the tyranny. or TCM and PCM. I will know more after Sunday of this week when I have time to look.
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