Last Modified: 06-05-2026 6.11:8.1.0 Doc ID: RM100000001D0YQ
Model Year Start: 2019 Model: Corolla Prod Date Range: [06/2018 - 09/2022]
Title: K120 / K121 (CVT): K120 CONTINUOUSLY VARIABLE TRANSAXLE SYSTEM: ECU Power Source Circuit; 2019 - 2022 MY Corolla Corolla Hatchback [06/2018 - 09/2022]

ECU Power Source Circuit

DESCRIPTION

When the engine switch is turned on (IG), battery voltage is applied to terminal MREL of the ECM through the coil of the EFI-MAIN relay. This causes the EFI-MAIN relay to close, which supplies power to terminal +B of the TCM.

WIRING DIAGRAM

Refer to DTC U010087.

Click here 2019 - 2022 MY Corolla Corolla Hatchback [06/2018 - 09/2022]; K120 / K121 (CVT): K120 CONTINUOUSLY VARIABLE TRANSAXLE SYSTEM: U010087; Lost Communication with ECM/PCM "A" Missing Message

CAUTION / NOTICE / HINT

NOTICE:

  • Inspect the fuses for circuits related to this system before performing the following procedure.
  • Perform registration and/or initialization when parts related to the continuously variable transaxle system are replaced.

    Click here 2019 MY Corolla Hatchback [06/2018 - 01/2019]; K120 / K121 (CVT): K120 CONTINUOUSLY VARIABLE TRANSAXLE SYSTEM: PRECAUTION 2020 - 2022 MY Corolla Corolla Hatchback [01/2019 - 09/2022]; K120 / K121 (CVT): K120 CONTINUOUSLY VARIABLE TRANSAXLE SYSTEM: PRECAUTION

PROCEDURE

1.

CHECK HARNESS AND CONNECTOR (TCM - BODY GROUND)

(a) Disconnect the C80 TCM connector.

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

Standard Resistance

Tester Connection

Condition

Specified Condition

C80-2 (E1) - Body ground

Always

Below 1 Ω

(c) Connect the C80 TCM connector.

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

2.

INSPECT ECU TERMINAL VOLTAGE (+B TERMINAL)

(a) Disconnect the C80 TCM connector.

(b) Turn the engine switch on (IG).

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

Standard Voltage

Tester Connection

Condition

Specified Condition

C80-1 (+B) - Body ground

Engine switch on (IG)

11 to 14 V

(d) Connect the C80 TCM connector.

OK

CHECK FOR INTERMITTENT PROBLEMS

NG

3.

CHECK HARNESS AND CONNECTOR (TCM - NO. 1 INTEGRATION RELAY)

(a) Disconnect the 1B No. 1 integration relay connector.

(b) Disconnect the C80 TCM connector.

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

Standard Resistance (Check for Open)

Tester Connection

Condition

Specified Condition

C80-1 (+B) - 1B-4

Always

Below 1 Ω

C80-1 (+B) or 1B-4 - Body ground

Always

10 kΩ or higher

(d) Connect the C80 TCM connector.

(e) Connect the 1B No. 1 integration relay connector.

OK

GO TO ECM POWER SOURCE CIRCUIT (ENGINE CONTROL SYSTEM / SFI SYSTEM)

Click here 2019 MY Corolla Hatchback [06/2018 - 01/2019]; M20A-FKS (ENGINE CONTROL): SFI SYSTEM: ECM Power Source Circuit 2020 - 2022 MY Corolla Corolla Hatchback [01/2019 - 09/2022]; M20A-FKS (ENGINE CONTROL): SFI SYSTEM: ECM Power Source Circuit

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR