| 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 in GENERAL INFORMATION. |
Circuit Description
Note. Brake switch may also be referred to as stoplight switch.
This signal is used to detect that brakes have been applied. STP signal voltage is same as supplied to stoplights. STP signal is used mainly to control fuel cut-off engine speed (fuel cut-off engine speed is reduced slightly when vehicle is braking). DTC is set when stoplight switch does not turn off even when vehicle is driven (2 trip detection logic). Possible causes are
- Short in stop light switch signal circuit.
- Faulty stop light switch.
- Faulty ECM.
Diagnostic Aids
Read freeze frame data using hand-held tester or OBD-II scan tool, as freeze frame data records engine conditions when a malfunction is detected. When troubleshooting, it is useful to determine whether vehicle was running or stopped, engine was warmed up or not, air-fuel ratio was lean or rich, etc. at time of malfunction.