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
When engine is cranked, current flows from terminal ST of the ignition switch to the starter relay coil and also current flows to terminal STA of the ECM (STA signal). (Scheme 81)and (Scheme 82). When the STA signal and NE signal are input to the ECM, the Tr1 is turned ON, current flows to the coil of the circuit opening relay, the relay switches on, power is supplied to the fuel pump, and the fuel pump operates. While the NE signal is generated (engine running), the ECM keeps the Tr1 ON (circuit opening relay ON) and the fuel pump also keeps operating. The fuel pump speed is controlled at 2 levels (high speed or low speed) by the condition of the engine (starting, light load, heavy load). When the engine starts (STA ON), the Tr2 in the ECM is OFF, so the fuel pump relay closes and battery positive voltage is applied directly to the fuel pump. The fuel pump operates at high speed. After the engine starts during idling or light loads, since the Tr2 goes ON, power is supplied to the fuel pump via the fuel pump resistor. The fuel pump operates at low speed. DTC is set when there is an open or short in fuel pump relay circuit. Possible causes are
- Open or short in fuel pump relay circuit.
- Faulty fuel pump relay.
- Faulty ECM.
Scheme 81
Scheme 82
Diagnostic Aids
Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.
Scheme 83
Scheme 84
Scheme 85
- Measure the voltage between terminal E1 and FPR of E6 and E3 ECM connectors. (Scheme 83) With STA signal on, 9-14 volts should be present. With STA signal OFF, 0-3 volts should be present. If okay, go to next step. If not okay, check and replace ECM.
- Remove fuel pump relay from engine room No. 2 relay block. Continuity should always be present between terminals No. 1 and 2. No continuity should be present between terminals No. 3 and 4. With battery voltage applied between terminals No. 1 and 2, continuity should be present between terminals No. 3 and 4. (Scheme 84) Replace relay as necessary. If okay, go to next step.
- Disconnect the E6 ECM connector. Check the continuity between the wire harness side connectors. Continuity should be present between fuel pump relay terminal No. 1 of relay block and +FPR (E6-15) terminals. No continuity should be present between fuel pump relay terminal No. 1 of relay block or +FPR (E6-15) - E1 (E3-7) terminals. (Scheme 85) Repair wiring as necessary. If okay, check and replace ECM.