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A code means...SAE U2105...car will not start..ran codes only one that

Customer Question
need to know wut a...
need to know wut a code means...SAE U2105...car will not start..ran codes only one that came up????
Submitted: 7 years ago.Category: Saturn
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Answered in 7 minutes by:
12/28/2009
Saturn Mechanic: Ivan, ASE Certified Master Technician replied 7 years ago
Ivan
Ivan, ASE Certified Master Technician
Category: Saturn
Satisfied Customers: 4,871
Experience: ASE Master Tech w/ 20+ years in the field. Self employed for 9 years. Member of AUTOLAB radio show
Verified

Hello Jarred. I'm going to send you everything I have for that code. Basically you have a communication problem between modules. Here is a diagram, description and some trouble shooting.

 

Your JA Expert,

Ivan

 

U2105

 

Schematic

CIRCUIT DESCRIPTION
The engine control module (ECM), transaxle control module (TCM) and Body Control Module (BCM) communicate normal mode messages over the controller area network (CAN) link circuits 2500 and 2501. Each controller on the CAN link uses a variable pulse width modulated square wave consisting of logic "0s" and logic "1s". A logic "0" is denoted as circuit 2501 at 1.5 volts with circuit 2500 at 3.5 volts resulting in a difference of 2 volts across the circuits. A logic "1" is denoted as both circuit 2500 and 2501 at 2.5 volts resulting in a difference of 0 volts across the circuits.

State of health messages are sent from each CAN controller on the link when the ignition is turned On as well as during normal vehicle operation. These messages allow the BCM, ECM and TCM to know that each controller on the link is functioning correctly. The ECM monitors the CAN link for low and high voltage faults. All controllers on the CAN link monitor each others messages and can set a DTC if information is not received. DTC U2105 sets when a specific controller has lost communications with the ECM.

DTC PARAMETERS
DTC U2105 will set if the BCM or TCM lost CAN communications with the ECM when:

  • Condition exists for longer than 2 seconds for TCM, 3 seconds for BCM
  • Ignition is On

DTC U2105 diagnostic runs continuously with ignition On.
DTC U2105 is a type A DTC for TCM.
DTC U2105 is a type C DTC for BCM.

DIAGNOSTIC AIDS

IMPORTANT: If DTC U2100 is also set in the ECM, diagnose that DTC first. If a circuit fault occurs on the CAN link, the BCM and/or TCM will set DTC U2105.

Check ECM mounting bolts for tightness and corrosion. The TCM sends the ECM vehicle speed over the CAN link. The ECM sends the BCM fuel level over the link as well. If the ECM is not communicating on the CAN link, vehicle speed in Scan tool ECM DATA TABLE will read 0 mph (with vehicle moving) and the fuel gauge on the I/P cluster will read EMPTY. This may he used for intermittent diagnosis.

With ignition On, each CAN high or CAN low circuit should have between 1.5 and 3.5 volts measuring into a control module no matter how many modules are left connected.

An open anywhere in the CAN link will result in at least one controller not communicating.

TEST DESCRIPTION

Diagnostic Chart Part 1

Diagnostic Chart Part 2

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Customer reply replied 7 years ago
could this have anything to do with a remote start...what is BCM exactly?..sayin just a harness behind glove compartment
Saturn Mechanic: Ivan, ASE Certified Master Technician replied 7 years ago
The BCM is the Body Control Module. It is responsible from everything from windshield wiper operation, to door locks, windows and HVAC. It is a central module to almost everything in the car. Did you recently have remote start system installed?
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Customer reply replied 7 years ago

remote start was installed a year ago...checked bcm fuse and was fine...is bcm a relay or fuse and where is it located on car..to check or change..something i can do or a dealer has to...sorry just tryin to say can i fix it at home since car wont start..thank u so much been alot of help ivan..

Saturn Mechanic: Ivan, ASE Certified Master Technician replied 7 years ago
This is something that the dealer or a facility will need to help you with. With communication issues, scan tools are an intregal part of the diagnostics. It is very difficult if not impossible to do it without one. The BCM is a module, it does have fuses that supply it with power, no relays, but since this involves several modules, the problem could be with any of them.
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Saturn Mechanic: Ivan, ASE Certified Master Technician replied 7 years ago

Hello, just checking in to see how you are making out with your car.

 

Ivan

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Ivan
Ivan
Ivan, ASE Certified Master Technician
Category: Saturn
Satisfied Customers: 4,871
4,871 Satisfied Customers
Experience: ASE Master Tech w/ 20+ years in the field. Self employed for 9 years. Member of AUTOLAB radio show

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