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 FFACTORY 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 | Refer To |
|---|---|---|
| Engine does not crank (Does not start) | Battery | Refer to ON-VEHICLE INSPECTION |
| Smart access system with push-button start | Refer to HOW TO PROCEED WITH TROUBLESHOOTING | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| VC output circuit | Refer to VC Output Circuit | |
| Cranking holding function circuit | Refer to Cranking Holding Function Circuit | |
| Starter | Refer to INSPECTION | |
| No initial combustion (Does not start) | Immobiliser system | Refer to HOW TO PROCEED WITH TROUBLESHOOTING |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| VC output circuit | Refer to VC Output Circuit | |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Crankshaft position sensor | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Valve timing | Refer to PROCEDURE - Step 3 | |
| 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 | |
| Compression | Refer to ON-VEHICLE INSPECTION - Step 9 | |
| Engine coolant temperature sensor | Refer to INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| Throttle body | Refer to ON-VEHICLE INSPECTION | |
| 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 |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel line | - | |
| Fuel injector for direct injection | Refer to INSPECTION | |
| Fuel injector for port injection | Refer to INSPECTION | |
| Crankshaft position sensor | Refer to ON-VEHICLE INSPECTION | |
| High engine speed (Poor idle) | Air conditioning signal circuit | Refer to PROBLEM SYMPTOMS TABLE |
| Throttle body | Refer to ON-VEHICLE INSPECTION | |
| Throttle body control | - | |
| Engine coolant temperature sensor | Refer to INSPECTION | |
| PCV hose | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| PCV system | Refer to ON-VEHICLE INSPECTION | |
| Low engine idle speed (Poor idle) | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| Electronic throttle control system | Refer to DTC P0120: Throttle / Pedal Position Sensor / Switch "A" Circuit Malfunction; DTC P0121: Throttle / Pedal Position Sensor / Switch "A" Circuit Range / Performance Problem; DTC P0122: Throttle / Pedal Position Sensor / Switch "A" Circuit Low Input; DTC P0123: Throttle / Pedal Position Sensor / Switch "A" Circuit High Input; DTC P0220: Throttle / Pedal Position Sensor / Switch "B" Circuit; DTC P0222: Throttle / Pedal Position Sensor / Switch "B" Circuit Low Input; DTC P0223: Throttle / Pedal Position Sensor / Switch "B" Circuit High Input; DTC P2135: Throttle / Pedal Position Sensor / Switch "A" / "B" Voltage Correlation | |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| PCV hose | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| Rough idle | Compression | Refer to ON-VEHICLE INSPECTION - Step 9 |
| Air fuel ratio sensor | Refer to ON-VEHICLE INSPECTION | |
| Heated oxygen sensor | Refer to ON-VEHICLE 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 (clocked) | - | |
| Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| Electronic throttle control system | Refer to DTC P0120: Throttle / Pedal Position Sensor / Switch "A" Circuit Malfunction; DTC P0121: Throttle / Pedal Position Sensor / Switch "A" Circuit Range / Performance Problem; DTC P0122: Throttle / Pedal Position Sensor / Switch "A" Circuit Low Input; DTC P0123: Throttle / Pedal Position Sensor / Switch "A" Circuit High Input; DTC P0220: Throttle / Pedal Position Sensor / Switch "B" Circuit; DTC P0222: Throttle / Pedal Position Sensor / Switch "B" Circuit Low Input; DTC P0223: Throttle / Pedal Position Sensor / Switch "B" Circuit High Input; DTC P2135: Throttle / Pedal Position Sensor / Switch "A" / "B" Voltage Correlation | |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| PCV hose | Refer to ON-VEHICLE INSPECTION - Step 1 | |
| Hunting (Poor idle) | PCV hose | Refer to ON-VEHICLE INSPECTION - Step 1 |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Air fuel ratio sensor | Refer to ON-VEHICLE INSPECTION | |
| Hesitation/Poor acceleration (Poor driveability) | Fuel line | - |
| Fuel pump for high pressure | Refer to ON-VEHICLE INSPECTION | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Valve timing | Refer to PROCEDURE - Step 3 | |
| Throttle body | Refer to ON-VEHICLE INSPECTION | |
| Knock sensor | Refer to INSPECTION | |
| Brake override system | Refer to Brake Override System | |
| Surging (Poor driveability) | Fuel line | - |
| 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 for port injection | Refer to INSPECTION | |
| Fuel injector for direct injection | Refer to INSPECTION | |
| Engine stalls soon after starting | Mass air flow meter | Refer to ON-VEHICLE INSPECTION |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| Fuel line | - | |
| Engine stalls during A/C operation | Air conditioning signal circuit (compressor circuit) | Refer to PROBLEM SYMPTOMS TABLE |
| ECM | Refer to REMOVAL | |
| Unable/difficult to refuel | Refueling valve (canister) | Refer to INSPECTION |
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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