DTC Test 51: Idle Signal Circuit
WARNING: This page is about a different car, the 1997 Lexus SC 300. However, it is still accessible from the selected car via links, so may be relevant.
- Remove cruise control ECU with electrical connectors still attached. Disconnect engine ECU and ABS/TRAC ECU. Turn ignition on. Measure voltage at terminal No. 21 of cruise control ECU connector. See Figure. Battery voltage should exist with throttle wide open, and less than 2 volts should exist with throttle closed.
- If voltage is not as specified, go to next step. If voltage is as specified:
- CODE - Check for intermittent condition (poor connections, etc.). If connections are okay, replace cruise control ECU.
- NO CODE - Perform next procedure listed in DIAGNOSIS BY SYMPTOM table in TROUBLE SHOOTING.
- Check for faulty circuit between ECM and Throttle Position Sensor (TPS). If circuit is not okay, check wiring harness and harness connectors for loose connections. Repair as necessary. If circuit is okay, go to next step.
- Disconnect TPS. Check TPS resistance with throttle closed and wide open. See THROTTLE POSITION SENSOR RESISTANCE table.
THROTTLE POSITION SENSOR RESISTANCE
| Application | Terminals No. | Ohms |
|---|---|---|
| Throttle Open | 2 & 3 | 000-10,000 |
| Throttle Closed | 2 & 3 | 700-6300 |
| Throttle Open | 3 & 4 | One Megohm Or More |
| Throttle Closed | 3 & 4 | 2300 Ohms Or Less |
If resistance is not as specified, replace TPS. If resistance is as specified, check wiring. If wiring is okay, replace cruise control ECU.