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### DTC P0571 Stop Light Switch Circuit Malfunction

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## DESCRIPTION

While driving with cruise control, if the ECM detects that the brake pedal is depressed, the cruise control system will be canceled. The stop light switch sends brake pedal status signals to the ECM. When the brake pedal is not depressed, terminal ST1- is equal to the positive (+) battery voltage and terminal STP is below 1 V. When the brake pedal is depressed, the ECM cancels cruise control operation. The ECM outputs this DTC when the voltage of terminals ST1- and STP are both below 1 V for 0.5 seconds or more at the same time. The fail-safe function operates to enable normal driving even if there is a malfunction in the stop light signal circuit.

DTC No. | DTC Detection Condition | Trouble Area

P0571

ECM detects malfunction of stop light switch circuit under both of following conditions:

1. Voltage of terminal STP is less than 1 V for 0.5 sec. or more
2. Voltage of terminal ST- is less than 1 V for 0.5 sec. or more

1. Stop light switch assembly
2. Stop light switch circuit
3. ECM

## WIRING DIAGRAM

## INSPECTION PROCEDURE

1.READ DATA LIST (STOP LIGHT SWITCH)

1. Connect the intelligent tester to the DLC3.

1. Turn the ignition switch ON, and turn the intelligent tester main switch ON.

1. Check the DATA LIST for proper functioning of the stop light switch.

ECM (Cruise control):
Item | Measurement Item / Display (Range) | Normal Condition | Diagnostic Note
Stp Light SW M-CPU | Stop light switch signal (Main CPU) / ON or OFF | ON: Brake pedal is depressed OFF: Brake pedal is released | -
Stp Light SW S1-CPU | Stop light switch signal (Sub CPU) / ON or OFF | ON: Brake pedal is depressed OFF: Brake pedal is released | -
Stp Light SW S2-CPU | Stop light switch signal (Sub CPU) / ON or OFF | ON: Brake pedal is depressed OFF: Brake pedal is released | -

OK:
  Display changes according to brake pedal operation described in above table.

HINT:

1. Stop light SW1 indicates the input of the ST1-terminal, and stop light SW2 indicates the input of the STP terminal.

| OK |

REPLACE ECM

NG |

2.INSPECT FUSE (STOP, IGN)

1. Remove the STOP and IGN fuses from the instrument panel junction block.

1. Measure the resistance of the fuses.

   Standard resistance:
     Below 1 Ω

| NG |

REPLACE STOP LIGHT SWITCH

OK |

3.INSPECT STOP LIGHT SWITCH

1. Disconnect the S14 stop light switch connector.

1. Measure the resistance of the switch.

   Standard resistance:

     Tester Connection | Switch Condition | Specified Condition
     1 - 2 | Not pushed | Below 1 Ω
     3 - 4 | Not pushed | 10 kΩ or higher
     1 - 2 | Pushed | 10 kΩ or higher
     3 - 4 | Pushed | Below 1 Ω

| NG |

REPLACE STOP LIGHT SWITCH ASSEMBLY

OK |

4.CHECK WIRE HARNESS

1. Measure the voltage of the wire harness side connector.

   Standard voltage:

     Tester Connection | Condition | Specified Condition
     S14-2 - Body ground | Always | 10 to 14 V
     S14-3 - Body ground | Ignition switch ON | 10 to 14 V

| NG |

REPAIR OR REPLACE WIRE HARNESS AND CONNECTOR (STOP LIGHT SWITCH - ECM)

OK |

5.CHECK ECM (STP, ST1- VOLTAGE)

1. Reconnect the stop light switch connector.

1. Disconnect the E14 or E6 connectors from the ECM.

1. Turn the ignition switch ON.

1. Measure the voltage of the wire harness side connector.

   Standard voltage:
     1GR-FE:

     Tester Connection | Brake Pedal Condition | Specified Condition
     E14-15 (STP) - Body ground | Depressed | 10 to 14 V
     E14-15 (STP) - Body ground | Released | Below 1 V
     E14-16 (ST1-) - Body ground | Depressed | Below 1 V
     E14-16 (ST1-) - Body ground | Released | 10 to 14 V

     1KD-FTV:

     Tester Connection | Brake Pedal Condition | Specified Condition
     E6-15 (STP) - Body ground | Depressed | 10 to 14 V
     E6-15 (STP) - Body ground | Released | Below 1 V
     E6-14 (ST1-) - Body ground | Depressed | Below 1 V
     E6-14 (ST1-) - Body ground | Released | 10 to 14 V

| NG |

REPAIR OR REPLACE WIRE HARNESS AND CONNECTOR (STOP LIGHT SWITCH - ECM)

OK |

REPLACE ECM