Brake switch is connected to brake pedal and transmits brake operating state to ECM.
When the output signal of APS is higher than what driver intended during driving (e.g. short to high voltage line in APS circuit, false signal ), driver depresses brake pedal.
Like this, if driver′s decelerating intension is transmitted to ECM (break pedal depressed)when APS output voltage is high, ECM recognizes APS trouble and Limp Home mode is activated.
At Limp Home mode, engine speed is fixed at 1200RPM and engine power generation is limitted.
Even at Limp home mode, if correct APS signal is detected, Limp Home mode is deactivated.
Brake switch, which monitors proper operation of APS, is devided 1 and 2 for the fidelity of brake switch.
When brake switch operates correctly, switch 1 is OFF and switch 2 is ON when releasing brake pedal, while switch 1 is ON and switch 2 is OFF when depressing brake pedal. thus when the signal from a switch is different from the other′s, brake switch is in good condition. When the signal from a switch is same as the other′s, brake switch is fault.
Item | Detecting Condition | Possible Cause | ||
DTC Strategy | ● Signal monitoring | ● Brake switch component ● Abnormal brake pedal height ● Brake switch circuit | ||
Enable Conditions | ● IG KEY "ON" | |||
Threshold Value | ● Wiring open | |||
Diagnostic Time | ● 100 sec. | |||
Fail Safe | Fuel cut | NO | ||
EGR Off | NO | |||
Fuel Limit | NO | |||
Check Lamp | NO | |||
Condition | Brake Pedal Released | Brake Pedal Depressed | ||
switch activated | Switch 1 | Switch 2 | Switch1 | Switch 2 |
OFF | ON | ON | OFF | |
Fig.1) The waveform of brake signal 1 and 2 are measured simultaneously. Both waveforms are symmetrical.
Connect GDS to Data Link Connector (DLC).
Warm engine up to normal operating temperature.
Turn "OFF" electrical devices and A/C.
Monitor "BRAKE SWITCH" and "REDUNDANT BRAKE SWITCH" parameter on the GDS.
Specification : When brake pedal is released : "BRAKE SWITCH" and "REDUNDANT BRAKE SWITCH" : OFF
When brake pedal is depressed : "BRAKE SWITCH" and "REDUNDANT BRAKE SWITCH" : ON
Fig 1) Data when brake switch(brake pedal) is deactivated(released) : "BRAKE SWITCH" and "REDUNDANT BRAKE SWITCH" : OFF
Fig 2) Data when brake switch(brake pedal) is activated(depressed) : "BRAKE SWITCH" and "REDUNDANT BRAKE SWITCH" : ON
Electrical systems consist of a lot of harness and connectors, poor connection of terminals can cause various problems and damge of component.
Perform checking procedure as follows.
Check damage of harness and terminals : Check terminals for contact resistance, corrosion and deformation.
Check connecting condition of ECM and component connector : Check terminal seperation, damage of locking device and connecting condition between terminal and wiring.
Disconnect the pin which requires checking at male connector and insert it to the terminal at female connector for checking connecting condition. ( after checking, reconnect the pin at correct position. )
Is the problem found?
 | ▶ Repair the trouble causing part and go to "Verification of Vehicle Repair". |
 | ▶ Go to "Power Circuit Inspection". |
Check brake switch 1 "HOT AT ALL TIMES"
IG KEY "OFF", ENGINE "OFF".
Disconnect brake switch connector.
Measure the voltage between power input terminal of brake switch 1 harness connector and chassis ground.
Secification : 11.5V~13.0V
Is the measured voltage within the specification?
| ▶ Go to "2.Check brake switch 2 main relay power" as follows. |
| ▶ Repair STOP FUSE in I/P JUNCTION BOX and related circuit and go to "Verification of Vehicle Repair". |
Check brake switch 2 main relay power
IG KEY "OFF", ENGINE "OFF".
Disconnect brake switch connector.
IG KEY "ON".
Measure the voltage between power terminal of brake switch 2 harness connector and chassis ground.
Specification : 11.5V~13.0V
Is the measured voltage within the specification?
| ▶ Go to "Signal Circuit Inspection". |
| ▶ Repair SNSR1 FUSE in E/R JUNCTION BOX and related circuit and go to "Verification of Vehicle Repair". |
Check brake switch signal circuit voltage
IG KEY "OFF", ENGINE "OFF".
Connect brake switch connector and ECM connector.
Measure the voltage of ECM connector terminal 38 and 80 as depressing brake pedal.
Brake Pedal Released | Brake Pedal Depressed | |
Brake Switch Signal | 0.0V~0.1V | 11.5V~13.0V |
Redundant Brake Switch | 11.5V~13.0V | 0.0V~0.1V |
Is the measured voltage within the specification?
| ▶ Go to "Verification of Vehicle Repair". |
| ▶ If component has no problem after performing "Component Inspection" and go to "2. Check open in signal circuit". |
Check open in signal circuit
IG KEY "OFF", ENGINE "OFF".
Disconnect brake switch connector and ECM connector.
Check continuity between brake switch connector terminal 1 and ECM connector(CUD-K) terminal 38. (brake switch 1 circuit)
Check continuity between brake switch connector terminal 4 and ECM connector(CUD-K) terminal 80. (brake switch 2 circuit)
Specification : Continuity ( below 1.0Ω )
Is the measured resistance within the specification?
| ▶ Repair short in signal circuit and go to "Verification of Vehicle Repair". |
| ▶ Repair open in signal circuit and go to "Verification of Vehicle Repair". |
IG KEY "OFF", ENGINE "OFF".
Disconnect brake switch connector.
Check continuity between brake switch component terminal 1and 2 as depressing brake pedal. (brake switch 1)
Check continuity between brake switch component terminal 3and 4 as depressing brake pedal. (brake switch 2)
Brake Pedal Released | |
Brake Switch Signal | Redundant Brake Switch |
Discontinuity | Continuity |
Brake Pedal Depressed | |
Brake Switch Signal | Redundant Brake Switch |
Continuity | Discontinuity |
Does brake switch operate correctly?
| ▶ Go to "Verification of Vehicle Repair". |
| ▶ Unless any problem is detected after checking height of brake pedal, replace brake switch component and go to "Verification of Vehicle Repair". |
After a repair, it is essential to verify that the fault is corrected.
After connecting GDS select "Diagnostic Trouble Codes(DTCs)" mode to and then clear DTC.
Drive the vehicle within DTC Enable conditions in General information.
After selecting "Diagnostic Trouble Codes(DTCs)" mode and check DTC is recorded again.
Are any DTCs recorded ?
| ▶ Go to the DTC guide of recorded NO. in GDS. |
| ▶ System operates within specification. |
