Toyota 4Runner: Lost Communication with ECM / PCM "A" (U0100)

Toyota 4Runner Service Manual / Power Source / Network / Networking / Can Communication System / Lost Communication with ECM / PCM "A" (U0100)

DESCRIPTION

DTC Code	DTC Detection Condition	Trouble Area
U0100	There is no communication from the ECM.	Power source or inside ECM ECM main wire or connector ECM

HINT:

For vehicles with a smart key system only.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Inspect the fuses for circuits related to this system before performing the following inspection procedure.

HINT:

Operating the ignition switch, any switches or any doors triggers related ECU and sensor communication with the CAN, which causes resistance variation.

PROCEDURE

1.	DISCONNECT CABLE FROM NEGATIVE BATTERY TERMINAL

(a) Disconnect the cable from the negative (-) battery terminal before measuring the resistances of the main wire and branch wire.

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

NOTICE:

When disconnecting the cable, some systems need to be initialized after the cable is reconnected (See page ).

2.	CHECK FOR OPEN IN CAN BUS MAIN WIRE (ECM MAIN WIRE)

(a) Disconnect the F50 ECM connector.

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

Standard Resistance:

Tester Connection	Switch Condition	Specified Condition
F50-34 (CANP) - F50-33 (CANN)	Ignition switch off	108 to 132 Ω

Text in Illustration

*a	Rear view of wire harness connector (to ECM)

REPAIR OR REPLACE ECM MAIN WIRE OR CONNECTOR (CANP, CANN)

3.	CHECK HARNESS AND CONNECTOR (ECM - BATTERY AND BODY GROUND)

(a) Connect the cable to the negative (-) battery terminal.

NOTICE:

When disconnecting the cable, some systems need to be initialized after the cable is reconnected (See page ).

Text in Illustration

Front view of wire harness connector

(to ECM)

(b) Disconnect the B38, B39 and F51 ECM connectors.

Standard Resistance:

Tester Connection	Condition	Specified Condition
B38-12 (E1) - Body ground	Always	Below 1 Ω
B39-14 (E01) - Body ground	Always	Below 1 Ω
B39-15 (E02) - Body ground	Always	Below 1 Ω
B39-10 (ME01) - Body ground	Always	Below 1 Ω
F51-12 (EC) - Body ground	Always	Below 1 Ω

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
F51-24 (BATT) - Body ground	Always	11 to 14 V
F51-23 (+B2) - Body ground	Battery positive (+) voltage applied to terminal F51-9 (MREL)	11 to 14 V
F51-22 (+B) - Body ground	Battery positive (+) voltage applied to terminal F51-9 (MREL)	11 to 14 V

REPLACE ECM

REPAIR OR REPLACE HARNESS OR CONNECTOR

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