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

WARNING: This page is about a different car, the 2013 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 engine switch on (IG).

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

Standard Voltage

Tester Connection	Switch Condition	Specified Condition
E7-18 (+B) - E7-8 (E1)	Engine switch on (IG)	9 to 14 V

Turn the engine switch off.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
E7-8 (E1) - Body ground	Always	Below 1 Ω

TEXT IN ILLUSTRATION

*a	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.
Disconnect the ECM connector.

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

Standard Resistance

Tester Connection	Condition	Specified Condition
E7-6 (CAN+) - E26-31 (CAN+)	Always	Below 1 Ω
E7-7 (CAN-) - E26-1 (CAN-)	Always	Below 1 Ω
E7-6 (CAN+) or E26-31 (CAN+) - Body ground and other terminals	Always	10 kΩ or higher
E7-7 (CAN-) or E26-1 (CAN-) - Body ground and other terminals	Always	10 kΩ 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

REPLACE ECM. Refer to COMPONENTS
REPLACE TCM. Refer to COMPONENTS