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

WARNING: This page is about a different variant/trim than selected.

CHECK ECU TERMINAL VOLTAGE (+B AND E1 TERMINALS)

Disconnect the TCM connector.

Fig 1: Identifying TCM Connector
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Turn the ignition switch to ON.

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

Standard Voltage

Tester Connection	Switch Condition	Specified Condition
B52-18 (+B) - B52-8 (E1)	Ignition switch ON	9 to 14 V

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

Standard Resistance

Tester Connection	Condition	Specified Condition
B52-8 (E1) - Body ground	Always	Below 1 Ω

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 TCM & ECM Connectors
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
B52-6 (CAN+) - B51-30 (CAN+)	Always	Below 1 Ω
B52-7 (CAN-) - B51-36 (CAN-)	Always	Below 1 Ω
B52-6 (CAN+) or B51-30 (CAN+) - Body ground or other terminals	Always	1 MΩ or higher
B52-7 (CAN-) or B51-36 (CAN-) - Body ground or other terminals	Always	1 MΩ or higher

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