DTC U0100: Lost Communication with ECM / PCM "A": Procedure

WARNING: This page is about a different car, the 2010 Toyota Camry. However, it is still accessible from the selected car via links, so may be relevant.

CHECK ECU TERMINAL VOLTAGE (+B AND E1 TERMINALS)

Disconnect the TCM connector.

Fig 1: Checking ECU Terminal Voltage (+B And E1 Terminals)
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Turn the ignition switch on (IG).

Measure the voltage of the TCM connectors.

Standard voltage

Tester Connection	Specified Condition
C56-18 (+B) - C56-8 (E1)	9 to 14 V

Turn the ignition switch off.

Measure the resistance of the TCM connector.

Standard resistance

Tester Connection	Specified Condition
C56-8 (E1) - Body ground	Below 1 Ω

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

CHECK HARNESS AND CONNECTOR (TCM - ECM)

Disconnect the C56 TCM connector.

Fig 2: Identifying C56 TCM And C55 ECM Connector Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Disconnect the C55 ECM connector.

Measure the resistance of the wire harness side connectors.

Standard resistance

Tester Connection	Specified Condition
C56-6 (CAN+) - C55-2 (CAN+)	Below 1 Ω
C56-7 (CAN-) - C55-1 (CAN-)	Below 1 Ω
C56-6 (CAN+) or C55-2 (CAN+) - Body ground	1 MΩ or more
C56-7 (CAN-) or C55-1 (CAN-) - Body ground	1 MΩ or more

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

CHECK IF DTC OUTPUT RECURS

Connect Techstream to the DLC3.
Clear the DTC.
Replace the TCM.
HINT:

Replace the TCM with a TCM from a normally functioning vehicle of the same model.
Start the engine.

Read the DTCs.

Display (DTC Output)	Proceed to
P0100	A
No DTC	B

B → REPLACE TCM

A → REPLACE ECM