Note. For information on engine immobilizer system, see COMPUTERIZED ENGINE CONTROLS in THEORY & OPERATION article.
| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article. |
Circuit Description
Note. Brake switch may also be referred to as stop light switch.
In this system, the signal of the stop light switch is used to judge whether the acceleration system is abnormal or not. The stop light switch has a duplex system (signals STP and ST1-) to memorize the abnormality when signals of depressing and releasing brake pedal are detected simultaneously. See BRAKE SWITCH OPERATION table. DTC P0504 will set when brake switch signal is not present. Possible causes are
- Short in stop light switch signal circuit.
- Faulty stop light switch.
- Faulty ECM.
| Signal | Brake Pedal Released | In Transition | Brake Pedal Depressed |
|---|---|---|---|
| STP | OFF | ON | ON |
| ST1 | ON | ON | OFF |
BRAKE SWITCH OPERATION
Diagnostic Aids
Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.
Scheme 148
Scheme 149
Scheme 150
- Check if the stop lights go on and off normally when the brake pedal is operated and released. If okay, go to next step. If not okay, repair stop light circuit.
- If using hand-held tester, connect the hand-held tester to the DLC3. Turn the ignition switch ON and push the hand-held tester ON. Read the STP signal on the hand-held tester. With brake pedal depressed, STP signal should be ON. With brake pedal released, STP signal should be OFF. If okay, check for intermittent problems. If not okay, go to next step.
- Disconnect the D2 driver side junction block ECU 18-pin connector. (Scheme 148) Disconnect the ECM E5 connector. (Scheme 149) Check continuity between the wire harness side connectors. See «DRIVER SIDE JUNCTION BLOCK/ECM CONTINUITY»(ref-151781-S02680774362003030300000) table. If continuity is to specification, check and replace ECM. If continuity is not to specification, repair or replace harness or connector as necessary. DRIVER SIDE JUNCTION BLOCK/ECM CONTINUITY Terminals Specification STPO (D2-12) - STP (E5-4) Continuity STPO (D2-12) Or STP (E5-4) - E1 (E3-7) No Continuity
- Check stop light switch by measuring voltage between ECM terminals E1 and STP. See «CHECKING STOP LIGHT SWITCH»(ref-151781-S39107549642003092400000). (Scheme 150) Replace stop light switch as necessary. If okay, go to next step. CHECKING STOP LIGHT SWITCH Brake Pedal Position Voltage Depressed 7.5-14 Released Less Than 1.5
- Check harness and connector between ECM and stop light switch. Repair as necessary. If okay, replace ECM.