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 250C Automatic TransFACTORY OEM SERVICE PROCEDURE
Problem Symptoms Table
HINT:
- Use the table below to help determine the cause of problem symptoms. If multiple suspected areas are listed, the potential causes 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.
- Inspect the fuses and relays related to this system before inspecting the suspected areas below.
SFI SYSTEM
| Symptom | Suspected Area | See |
|---|---|---|
| Engine does not crank (Does not start) | Battery | Refer to ON-VEHICLE INSPECTION |
| Cranking holding function circuit | Refer to Cranking Holding Function Circuit | |
| Smart access system with push button start | Refer to PROBLEM SYMPTOMS TABLE | |
| Starter assembly | Refer to INSPECTION | |
| VC output circuit (ECM 5 V output) | Refer to VC Output Circuit | |
| No initial combustion (Does not start) | Immobilizer system | Refer to PROBLEM SYMPTOMS TABLE |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| VC output circuit (ECM 5 V output) | Refer to VC Output Circuit | |
| Crankshaft position sensor | Refer to INSPECTION | |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Valve timing | Refer to PROCEDURE - Step 4 | |
| Engine cranks normally but difficult to start | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| Engine coolant temperature sensor | Refer to INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector assembly | Refer to INSPECTION | |
| Compression | Refer to ON-VEHICLE INSPECTION - Step 10 | |
| Intake system | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| Throttle body assembly | Refer to INSPECTION | |
| Cold start injector circuit | Refer to Cold Start Injector Circuit | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Incomplete intermittent combustion occurs (Does not start) | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| Fuel line | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector assembly | Refer to INSPECTION | |
| Crankshaft position sensor | Refer to INSPECTION | |
| Valve timing | Refer to PROCEDURE - Step 4 | |
| High engine speed (Poor idle) | Air conditioning signal circuit | Refer to PROBLEM SYMPTOMS TABLE |
| Throttle body assembly | Refer to INSPECTION | |
| Throttle body assembly control | Refer to ON-VEHICLE INSPECTION | |
| Engine coolant temperature sensor | Refer to INSPECTION | |
| PCV hose | Refer to ON-VEHICLE INSPECTION | |
| PCV system | Refer to INSPECTION | |
| ACIS control circuit | Refer to ACIS Control Circuit | |
| Low engine speed (Poor idle) | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Throttle body assembly | Refer to INSPECTION | |
| Throttle body assembly control | Refer to ON-VEHICLE INSPECTION | |
| Intake system | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| ACIS control circuit | Refer to ACIS Control Circuit | |
| PCV hose | Refer to ON-VEHICLE INSPECTION | |
| PCV system | Refer to INSPECTION | |
| Engine stalls on deceleration | Idle speed (refer to "Low engine speed") | Refer to ON-VEHICLE INSPECTION - Step 9 |
| Rough idle | Compression (engine mechanical) | Refer to ON-VEHICLE INSPECTION - Step 10 |
| Air fuel ratio sensor | Refer to INSPECTION | |
| Heated oxygen sensor | Refer to INSPECTION | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Air conditioning signal circuit | Refer to PROBLEM SYMPTOMS TABLE | |
| Fuel line | Refer to ON-VEHICLE INSPECTION | |
| Valve timing | Refer to PROCEDURE - Step 4 | |
| Fuel pump for low or high pressure | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| Intake system | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| ACIS control circuit | Refer to ACIS Control Circuit | |
| PCV hose | Refer to ON-VEHICLE INSPECTION | |
| PCV system | Refer to INSPECTION | |
| Hunting (Poor idle) | PCV hose | Refer to ON-VEHICLE INSPECTION |
| PCV system | Refer to INSPECTION | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Air fuel ratio sensor | Refer to INSPECTION | |
| ACIS control circuit | Refer to ACIS Control Circuit | |
| Engine stalls during air conditioning operation | Air conditioning signal circuit (compressor circuit) | Refer to PROBLEM SYMPTOMS TABLE |
| ECM | Refer to REMOVAL | |
| Cold start injector circuit | Refer to Cold Start Injector Circuit | |
| Hesitation/Poor acceleration (Poor driveability) | Fuel line | Refer to ON-VEHICLE INSPECTION |
| Fuel pump for low or high pressure | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| Valve timing | Refer to PROCEDURE - Step 4 | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Throttle body assembly | Refer to INSPECTION | |
| Knock control sensor | Refer to INSPECTION | |
| Brake override system | Refer to Brake Override System | |
| Surging (Poor driveability) | Fuel line | Refer to ON-VEHICLE INSPECTION |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector assembly | Refer to INSPECTION | |
| Engine stalls soon after starting | Mass air flow meter | Refer to ON-VEHICLE INSPECTION |
| Intake system | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| Fuel line | Refer to ON-VEHICLE INSPECTION | |
| Cold start injector circuit | Refer to Cold Start Injector Circuit | |
| Unable/difficult to refuel | 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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