STOP AND START SYSTEM, Diagnostic DTC:P1541

DTC Code	DTC Name
P1541	Brake Booster Sensor Circuit

DESCRIPTION

This description and the following Inspection Procedure are for DTC P1541 which is stored in the engine stop and start ECU. When the engine is stopped due to Stop and Start system control, no vacuum is supplied to the brake booster and the stored vacuum may be used up by depressing the brake pedal, resulting in insufficient brake force. To prevent this from occurring, if the vacuum drops below a threshold, the engine will be started.

To prevent inadequate brake force, if the vehicle speed exceeds a threshold, the engine will be started.

The vacuum sensor assembly is used to maintain a certain level of vacuum for system operation. If the vacuum sensor malfunctions, the engine will not be stopped.

DTC No.	DTC Detection Condition	Trouble Area
P1541	The following condition is met (1 trip detection logic): Vacuum does not change during brake pedal operation 3 times in a row.	Vacuum sensor assembly Brake booster Brake booster hose (vacuum hose) Engine stop and start ECU
P1541	All of the following conditions are met (1 trip detection logic): Vehicle speed exceeds 30 km/h (18.6 mph) 9 times or more. Vacuum change (difference between the maximum and minimum values) 0.3 kPa or less.	Vacuum sensor assembly Brake booster Brake booster hose (vacuum hose) Engine stop and start ECU

DTC No.

DTC Detection Condition

Trouble Area

P1541

The following condition is met (1 trip detection logic):

Vacuum does not change during brake pedal operation 3 times in a row.

Vacuum sensor assembly
Brake booster
Brake booster hose (vacuum hose)
Engine stop and start ECU

P1541

All of the following conditions are met (1 trip detection logic):

Vehicle speed exceeds 30 km/h (18.6 mph) 9 times or more.
Vacuum change (difference between the maximum and minimum values) 0.3 kPa or less.

Vacuum sensor assembly
Brake booster
Brake booster hose (vacuum hose)
Engine stop and start ECU

Tech Tips

DTCs for the Stop and Start system are not cleared even if the malfunction has been repaired. After repairing the malfunction, be sure to clear the DTCs Click here.

After troubleshooting, perform the following steps to recheck for DTCs.
Tech Tips
- If the battery terminal has been disconnected, the stop and start will be prohibited. In this case, drive the vehicle for 15 to 40 minutes to permit the stop and start operation.
- Allow the engine to idle for 3 minutes after the engine warms up and check that the engine speed is within 50 rpm of the target idle speed.
1. Connect the intelligent tester to the DLC3.
2. Clear the DTCs Click here.
3. Start the engine and warm it up.
4. Enter the following menus: Powertrain / Stop and Start / Data List / Brake Boost Pressure.
5. Drive the vehicle at 30 km/h (18.6 mph) or more and stop the vehicle. Repeat this driving pattern 9 times to allow the brake booster vacuum to change.
6. Stop the vehicle.
7. Check that no DTCs are output Click here.
Check if the Stop and Start system operates normally.
Tech Tips
- If the battery terminal has been disconnected, the stop and start will be prohibited. In this case, drive the vehicle for 15 to 40 minutes to permit the stop and start operation.
- Allow the engine to idle for 3 minutes after the engine warms up and check that the engine speed is within 50 rpm of the target idle speed.
1. for Manual transaxle
  1. Warm up the engine.
  2. Turn the air conditioning system off.
  3. Drive the vehicle at 7 km/h (4.3 mph) or more.
  4. Stop the vehicle. Move the shift lever to neutral and release the clutch pedal.
  5. Check that the engine stops.
  6. Depress the clutch pedal and check that the engine restarts.
2. for CVT
  1. Warm up the engine.
  2. Turn the air conditioning system off.
  3. Drive the vehicle at 7 km/h (4.3 mph) or more.
  4. Stop the vehicle with the shift lever in D and depressed the brake pedal.
  5. Check that the engine stops.
  6. Release the brake pedal and check that the engine restarts.

WIRING DIAGRAM

Refer to P1540 Click here.

CAUTION / NOTICE / HINT

Note

If the engine stop and start ECU is being replaced, register the previously recorded number of starter operations into the new engine stop and start ECU Click here.
After the engine stop and start ECU is replaced or after an air conditioner kit is installed, clear the A/C information stored in the engine stop and start ECU Click here.
After the engine stop and start ECU or airbag sensor assembly (yaw rate sensor) is replaced, initialize and calibrate 0 point of deceleration sensor Click here.

PROCEDURE

CHECK ANY OTHER DTCS OUTPUT

Connect the intelligent tester to the DLC3.
Turn the ignition switch to ON.
Turn the tester on.
Enter the following menus: Powertrain / Stop and Start / DTC.

Check for other DTCs.

Result
Result	Proceed to
Other DTC is not output	A
Other DTC is output	B

GO TO DTC CHART Click here

READ VALUE USING INTELLIGENT TESTER (BRAKE BOOST PRESSURE AND BRAKE NEGATIVE PRESSURE)

Connect the intelligent tester to the DLC3.
Start the engine. Wait for several minutes and stop the engine by turning the ignition switch off.
Turn the ignition switch to ON.
Turn the tester on.
Enter the following menus: Powertrain / Stop and Start / Data List / Brake Boost Pressure.

Depress the brake pedal 5 times and read the changes in the following pressure value.

Tech Tips

The changes in the value can be determined by comparing the pressure value before and after the brake pedal is depressed 5 times.

Standard

Tester Display	Switch Condition	Specified Condition
Brake Boost Pressure	Ignition switch ON Brake pedal depressed 5 times	Changes by 20 kPa (150 mmHg) or more

USE SIMULATION METHOD TO CHECK Click here

INSPECT BRAKE BOOSTER HOSE
1. Check the brake booster hose for cracks and clogging (visually check).
  
  Tech Tips
  
  When the actual brake force is insufficient check the brake booster assembly.
  
  OK
  
  No cracks or clogging in the brake booster hose.
NG
REPLACE BRAKE BOOSTER HOSE

OK
REPLACE VACUUM SENSOR ASSEMBLY
1. Replace the vacuum sensor assembly Click here.
NEXT

OK
No cracks or clogging in the brake booster hose.

CONFIRM DTC

Connect the intelligent tester to the DLC3.
Clear the DTCs Click here.
Start the engine and warm it up.
Enter the following menus: Powertrain / Stop and Start / Data List / Brake Boost Pressure.
Drive the vehicle at 30 km/h (18.6 mph) or more and stop the vehicle. Repeat this driving pattern 9 times to allow the brake booster vacuum to change.
Stop the vehicle.

Check that no DTCs are output Click here.

Result
Result	Proceed to
DTC is not output	A
DTC is output	B

END

REPLACE ENGINE STOP AND START ECU Click here