Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
2012 Lexus IS 350 Base, AWDFACTORY OEM SERVICE PROCEDURE
Problem Symptoms Table
HINT:
Use the table below to help determine the cause of the problem. The potential cases of the symptoms are listed in order of probability in the "Suspected area" column of the table. Check each symptom by checking the suspected areas in the order they are listed. Replace parts as necessary.
SFI SYSTEM
| Symptom | Suspected Area | Refer to |
|---|---|---|
| Engine does not crank (Does not start) | 1. Battery | Refer to ON-VEHICLE INSPECTION - Step 1 |
| 2. ECM power source circuit | Refer to ECM Power Source Circuit | |
| 3. VC output circuit | Refer to VC Output Circuit | |
| 4. Cranking holding function circuit | Refer to Cranking Holding Function Circuit | |
| 5. Starter | Refer to INSPECTION | |
| No initial combustion (Does not start) | 1. Immobiliser System | Refer to PROBLEM SYMPTOMS TABLE |
| 2. ECM power source circuit | Refer to ECM Power Source Circuit | |
| 3. Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| 4. ECM | Refer to REMOVAL | |
| Engine cranks normally but difficult to start | 1. Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| 2.Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| 3. Compression | Refer to ON-VEHICLE INSPECTION - Step 9 | |
| 4. ECM power source circuit | Refer to ECM Power Source Circuit | |
| Difficult to start with cold engine | 1. Cranking holding function circuit | Refer to Cranking Holding Function Circuit |
| 2. Ignition system | Refer to ON-VEHICLE INSPECTION | |
| 3. Spark plug | Refer to ON-VEHICLE INSPECTION - Step 3 | |
| 4. Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| 5. Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| 6. Fuel injector for direct injection | Refer to INSPECTION | |
| 7. Fuel injector for port injection | Refer to INSPECTION | |
| Difficult to start with worm engine | 1. Cranking holding function circuit | Refer to Cranking Holding Function Circuit |
| 2. Fuel injector for port injection | Refer to INSPECTION | |
| 3. Fuel injector for direct injection | Refer to INSPECTION | |
| 4. Ignition system | Refer to ON-VEHICLE INSPECTION | |
| 5. Spark plug | Refer to ON-VEHICLE INSPECTION - Step 3 | |
| 6. Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| 7. Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| High engine idle speed (Poor idling) | 1. ECM power source circuit | Refer to ECM Power Source Circuit |
| 2. A/C signal circuit (compressor circuit) | Refer to Air Conditioning Compressor Magnetic Clutch Circuit | |
| 3. Electronic throttle control system | Refer to ON-VEHICLE INSPECTION | |
| 4. Air induction system | - | |
| 5. PCV hose | Refer to ON-VEHICLE INSPECTION | |
| Low engine idle speed (Poor idling) | 1. A/C signal circuit (compressor circuit) | Refer to Air Conditioning Compressor Magnetic Clutch Circuit |
| 2. Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| 3. Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| 4. Electronic throttle control system | Refer to ON-VEHICLE INSPECTION | |
| 5. Air induction system | - | |
| 6. PCV hose | Refer to ON-VEHICLE INSPECTION | |
| Rough idling (Poor idling) | 1. Compression | Refer to ON-VEHICLE INSPECTION - Step 9 |
| 2. Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| 3. Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| 4. Electronic throttle control system | Refer to ON-VEHICLE INSPECTION | |
| 5. Air induction system | - | |
| 6. PCV hose | Refer to ON-VEHICLE INSPECTION | |
| Hunting (Poor idling) | 1. ECM power source circuit | Refer to ECM Power Source Circuit |
| 2. Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| 3. Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| 4. Spark plug | Refer to ON-VEHICLE INSPECTION - Step 3 | |
| 5. Ignition system | Refer to ON-VEHICLE INSPECTION | |
| 6. Fuel injector for port injection | Refer to INSPECTION | |
| 7. Fuel injector for direct injection | Refer to INSPECTION | |
| 8. Electronic throttle control system | Refer to ON-VEHICLE INSPECTION | |
| 9. Air induction system | - | |
| 10. PCV hose | Refer to ON-VEHICLE INSPECTION | |
| Hesitation/ Poor acceleration (Poor driveability) | 1. Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| 2. Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| 3. Spark plug | Refer to ON-VEHICLE INSPECTION - Step 3 | |
| 4. Ignition system | Refer to ON-VEHICLE INSPECTION | |
| 5. Fuel injector for port injection | Refer to INSPECTION | |
| 6. Fuel injector for direct injection | Refer to INSPECTION | |
| 7. Brake override system | Refer to Brake Override System | |
| Surging (Poor driveability) | 1. Spark plug | Refer to ON-VEHICLE INSPECTION - Step 3 |
| 2. Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| 3. Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| 4. Ignition system | Refer to ON-VEHICLE INSPECTION | |
| 5. Fuel injector for port injection | Refer to INSPECTION | |
| 6. Fuel injector for direct injection | Refer to INSPECTION | |
| Engine stalls soon after starting | 1. Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| 2. Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| 3. Spark plug | Refer to ON-VEHICLE INSPECTION - Step 3 | |
| 4. Ignition system | Refer to ON-VEHICLE INSPECTION | |
| 5. Fuel injector for port injection | Refer to INSPECTION | |
| 6. Fuel injector for direct injection | Refer to INSPECTION | |
| Engine stalls during A/C operation | 1. A/C signal circuit (Compressor circuit) | Refer to Air Conditioning Compressor Magnetic Clutch Circuit |
| 2. ECM | Refer to REMOVAL | |
| Unable/difficult refuel | 1. Fuel system (canister, refueling valve, roll over valve, fuel tank, etc.) | - |
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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