DTC U0100: Lost Communication with ECM / PCM "A" (TO 08/2009): Procedure

CHECK ECU TERMINAL VOLTAGE (+B AND E1 TERMINALS)

Disconnect the TCM connector.

Fig 1: Identifying D2 TCM Connector Terminal
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Turn the engine switch on (IG).

Measure the voltage according to the value(s) in the table below.

Standard Voltage

Tester Connection	Switch Condition	Specified Condition
D2-18 (+B) - D2-8 (E1)	Engine switch on (IG)	9 to 14 V

Measure the resistance according to the value(s) in the table below.

Standard Resistance

Tester Connection	Condition	Specified Condition
D2-8 (E1) - Body ground	Always	Below 1 Ω

TEXT IN ILLUSTRATION

*1	Front view of wire harness connector (to TCM)

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

CHECK HARNESS AND CONNECTOR (TCM - ECM)

Disconnect the TCM connector.

Fig 2: Identifying D2 TCM And D1 ECM Connector Terminals
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Disconnect the ECM connector.

Measure the resistance according to the value(s) in the table below.

Standard Resistance

Tester Connection	Condition	Specified Condition
D2-6 (CAN+) - D1-24 (CAN+)	Always	Below 1 Ω
D2-7 (CAN-) - D1-1 (CAN-)	Always	Below 1 Ω
D2-6 (CAN+) or D1-24 (CAN+) - Body ground or other terminals	Always	1 MΩ or higher
D2-7 (CAN-) or D1-1 (CAN-) - Body ground or other terminals	Always	1 MΩ or higher

TEXT IN ILLUSTRATION

*1	Front view of wire harness connector (to ECM)
*2	Front view of wire harness connector (to TCM)

NG → REPAIR OR REPLACE HARNESS OR CONNECTOR

OK: Go to next step

CHECK IF DTC OUTPUT RECURS

Connect the Techstream to the DLC3.
Clear the DTCs.
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.

Result

Display (DTC Output)	Proceed to
U0100	A
No DTC	B

B → See step 5

A → See step 4