DTC U0100: Lost Communication with ECM / PCM "A" [09/2014 - 11/2017]: Procedure

1. Disconnect the A71 ECM connector.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

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

2. Turn the engine switch on (IG).
3. Measure the voltage according to the value(s) in the table below.

   Standard Voltage

   Tester Connection	Condition	Specified Condition
   A71-1 (+B2) - Body ground	Engine switch on (IG)	11 to 14 V
   A71-2 (+B) - Body ground	Engine switch on (IG)	11 to 14 V

   Result

   Proceed to
   OK
   NG

Result: 

NG 

GO TO ECM POWER SOURCE CIRCUIT (ENGINE CONTROL SYSTEM / SFI SYSTEM). Refer to  ECM Power Source Circuit [09/2014 - 11/2017] 

Result: 

OK 

See step  2

1. Disconnect the F4 ECM connector.
2. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   F4-1 (E1) - Body ground	Always	Below 1 Ω

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR (ECM - BODY GROUND) 

Result: 

OK 

See step  3

1. Disconnect the A71 ECM connector.
2. Disconnect the A37 TCM connector.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   A71-10 (CAN+) - A37-21 (CAN+)	Always	Below 1 Ω
   A71-9 (CAN-) - A37-13 (CAN-)	Always	Below 1 Ω
   A71-10 (CAN+) or A37-21 (CAN+) - Body ground	Always	10 kΩ or higher
   A71-9 (CAN-) or A37-13 (CAN-) - Body ground	Always	10 kΩ or higher

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR 

Result: 

OK 

See step  4

1. Replace the TCM.

   Refer to COMPONENTS [09/2014 - 11/2017]

   HINT: 

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

   Result

   Proceed to
   NEXT

Result: 

NEXT 

See step  5

1. Clear the DTCs.

   Powertrain > ECT > Clear DTCs 

2. Start the engine.
3. Read the DTCs.

   Powertrain > ECT > Trouble Codes 

   Result

   Result	Proceed to
   DTCs are not output	A
   DTC U0100 is output	B

Result: 

A 

PERFORM A/T CODE REGISTRATION. Refer to  REGISTRATION [09/2014 - 11/2017] 

Result: 

B 

See step  6

1. Replace the ECM.

   Refer to COMPONENTS [09/2014 - 10/2015] , or refer to COMPONENTS [10/2015 - 11/2017]

   Result

   Proceed to
   NEXT

Result: 

NEXT 

PERFORM RESET MEMORY. Refer to  INITIALIZATION [09/2014 - 11/2017]