B0-RFA U1000 - what does this mean?
Thread Starter
Drifting
Joined: Jul 2004
Posts: 1,370
Likes: 8
B0-RFA U1000 - what does this mean?
Sitting idle at a stop signal and the engine idiot light started to flash. I did finally went away (stopped flashing) and the car runs fine. This happened twice. Looked up the code it threw out, B0-RFA U1000 = Loss of Communication with PCM.
Questions: What communication was loss to the "PCM"? What does P-C-M stand for? Is this serious? How to fix or should I ignore? Everything else appears to be find or working. THANKS!
(There are mods - see profile)
Questions: What communication was loss to the "PCM"? What does P-C-M stand for? Is this serious? How to fix or should I ignore? Everything else appears to be find or working. THANKS!
(There are mods - see profile)
Team Owner
Joined: Sep 2001
Posts: 23,283
Likes: 906
From: Lake Elsinore, CA
PCM = Power Control Module. It's the main computer in the car located just behind the left front wheel well.
Here's the code description from the sm:
DTC U1000 and U1255
Circuit Description
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation when operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least 1 critical parameter within about 5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. The DTC will only be reported once if more than 1 critical parameter does not have a sending module identification number associated with it.
Conditions for Running the DTC
Voltage supplied to the module is in the normal operating voltage range.
Diagnostic trouble codes U1300, U1301 or U1305 are not set.
The module setting the DTC requires serial data communication to occur.
Conditions for Setting the DTC
At least 1 critical operating parameter has not been associated with an identification number within about 5 seconds after beginning serial data communication.
Action Taken When the DTC Sets
The module uses a default value for the missing parameter.
Conditions for Clearing the DTC
A current DTC U1000 or U1255 will clear when all critical operating parameter for the module have been associated with an identification number or at the end of the current ignition cycle.
A history DTC resets after 50 ignition switch cycles with no repeated failure.
Diagnostic Aids
When a malfunction such as an open fuse to a module occurs while modules are communicating, a current DTC is set indicating lost communication with a specific module DTC. When the modules stop communicating, ignition is turned OFF, the current Lost Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so DTC U1000 or U1255 is set as current by the other modules. If the malfunction occurs when the modules are not communicating, only DTC U1000 or U1255 is set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
The modules which is not communicating is the likely cause of U1000 or U1255 being set. The following systems communicate on the class 2 serial data circuit:
The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
The module which set U1000 or U1255 is the likely cause of the malfunction.
Here's the code description from the sm:
DTC U1000 and U1255
Circuit Description
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation when operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least 1 critical parameter within about 5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. The DTC will only be reported once if more than 1 critical parameter does not have a sending module identification number associated with it.
Conditions for Running the DTC
Voltage supplied to the module is in the normal operating voltage range.
Diagnostic trouble codes U1300, U1301 or U1305 are not set.
The module setting the DTC requires serial data communication to occur.
Conditions for Setting the DTC
At least 1 critical operating parameter has not been associated with an identification number within about 5 seconds after beginning serial data communication.
Action Taken When the DTC Sets
The module uses a default value for the missing parameter.
Conditions for Clearing the DTC
A current DTC U1000 or U1255 will clear when all critical operating parameter for the module have been associated with an identification number or at the end of the current ignition cycle.
A history DTC resets after 50 ignition switch cycles with no repeated failure.
Diagnostic Aids
When a malfunction such as an open fuse to a module occurs while modules are communicating, a current DTC is set indicating lost communication with a specific module DTC. When the modules stop communicating, ignition is turned OFF, the current Lost Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so DTC U1000 or U1255 is set as current by the other modules. If the malfunction occurs when the modules are not communicating, only DTC U1000 or U1255 is set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
A Lost Communication with XXX DTC with a history status may indicate the cause of U1000 or U1255.
The modules which is not communicating is the likely cause of U1000 or U1255 being set. The following systems communicate on the class 2 serial data circuit:
- Body Control Module (BCM)
- Electronic Brake Control Module (EBCM)
- Electronic Suspension Control (ESC) Module
- HVAC (with CJ2)
- Sensing and Diagnostic Module (SDM)
- Instrument Panel Cluster (IPC)
- Driver Door Module (DDM)
- Passenger Door Module (PDM)
- Seat Control Module (SCM) (with AAB)
- Powertrain Control Module (PCM)
- Radio
- Remote Control Door Lock Receiver (RCDLR)
The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.
If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
The module which set U1000 or U1255 is the likely cause of the malfunction.
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,820
From: Charlotte, NC (formerly Endicott, NY)
One missed communication code isn't normally something you should worry about. The modules in the system pass State of Health messages back and forth on a continual basis. Some times these messages are missed due to electrical noise or other factors in the system. The next time the message is sent it may be received just fine but the previous code is not reset. If you see a lot of these codes then you need to start thinking of battery or data link problems.
This code will not cause the MIL to light or flicker so it was not the cause of the flickering you saw.
Bill
This code will not cause the MIL to light or flicker so it was not the cause of the flickering you saw.
Bill
Thanks for this information 
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
The Check Engine Light (CEL) will flash at you if the PCM detects a mis-fire condition. If your car has a lumpy radical cam, it can run fine but the cam lope can set a misfire DTC PCM-0300. If it flashes at you again, bring up the diagnostics while the engine is running. The DTC clears it self when you shut the engine down. My whiplash cam will cause my CEL to flash at low rpm when under load every once in a while.
BC
BC
