U2106

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 U2106 sets when a specific controller has lost communications with the TCM.

DTC PARAMETERS
DTC U2106 will set if the BCM or ECM lost CAN communications with the TCM when:
^ Condition exists for longer than 3 seconds for BCM, 25 seconds for ECM
^ Ignition is On for BCM, engine speed greater than 25 rpm

DTC U2106 diagnostic runs continuously with ignition On (BCM), engine cranking/running (ECM).
DTC U2106 is a type B DTC for ECM.
DTC U2106 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 short to ground/voltage occurs on the CAN link, the BCM and TCM will set U2107.

The TCM sends the BCM vehicle speed for the speedometer over the CAN link. If an open exists in either CAN high or CAN low circuit between the ECM and TCM, the tachometer will be inoperative.

The ECM sends the BCM tachometer RPM over the link. If an open exists in either CAN high or CAN low circuit between the ECM and BCM, the tachometer and speedometer will be inoperative.

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 a least one controller not communicating.

If main relay voltage is not present at the ECM as soon as the ignition is turned On, the ECM will NOT communicate over the CAN link; however it will communicate with the Scan tool. As soon as main relay voltage is present, the ECM will communicate over the voltage is later lost.

Check ECM mounting bolts for tightness and corrosion.

TEST

Diagnostic Chart: