Nissan Sentra B18 (2020-2025) Service Manual: U1040 Eng Comm Circuit

Dtc Description

DTC Description

DTC DETECTION LOGIC

DTC	CONSULT screen terms (Trouble diagnosis content)	DTC detection condition
U1040	ENG COMM CIRCUIT (Engine communication circuit)	Diagnosis condition	Ignition switch ON
		Signal (terminal)	Engine communication signal
		Threshold	ECM unable to transmit engine communication signal to generator
		Diagnosis delay time	—

POSSIBLE CAUSE

• Harness or connectors (LIN communication circuit is open or shorted.)

• ECM

FAIL-SAFE

Engine Control System

Engine operating condition in fail-safe mode
Fail safe mode		Nissan Sentra Vehicle behavior
Others		ECM operates active grille shutter to fully-open position.

Idle Start/Stop System

When a DTC is detected, the start/stop indicator lamp blinks slowly and the idle start/stop system operation is prohibited.

When ECM detects error while operating the idle start/stop system, ECM restarts the engine.

Confirmation Procedure

Confirmation Procedure

1. PRECONDITIONING

   If DTC Confirmation Procedure has been previously conducted, always perform the following procedure before conducting the next test.

   1. Turn ignition switch OFF and wait at least 10 seconds.

   2. Turn ignition switch ON.

   3. Turn ignition switch OFF and wait at least 10 seconds.

   >>

   GO TO 2.

2. PERFORM DTC CONFIRMATION PROCEDURE

   1. Turn ignition ON and wait at least 10 seconds.

   2. Check DTC.

   Is DTC detected?

   YES >>

   Refer to DTC Diagnosis Procedure.

   NO >>

   INSPECTION END

Dtc Diagnosis Procedure

DTC Diagnosis Procedure

1. CHECK LIN COMMUNICATION CIRCUIT

   1. Turn ignition switch OFF.

   2. Disconnect ECM harness connector and generator harness connector.

   3. Check the continuity between ECM harness connector and generator harness connector.

      ECM		Generator		Continuity
      Connector	Terminal	Connector	Terminal
      F25	98	F15	2	Existed

   4. Also check harness for short to power and short to ground.

   Is the inspection result normal?

   YES >>

   GO TO 2.

   NO >>

   Repair or replace error-detected parts.

2. REPLACE GENERATOR

   1. Replace generator. Refer to Removal and Installation.

   2. Erase DTC.

   3. Perform DTC confirmation procedure again. Refer to Confirmation Procedure.

   Is DTC detected again?

   YES >>

   Replace ECM. Refer to Removal & Installation.

   NO >>

   INSPECTION END