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 Toyota Sienna SEFACTORY 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 |
| Starter signal circuit | Refer to Starter Signal Circuit | |
| Starter | Refer to INSPECTION | |
| Starter relay | Refer to ON-VEHICLE INSPECTION | |
| Park/neutral position switch assembly | Refer to INSPECTION | |
| No initial combustion (Does not start) | ECM power source circuit | Refer to ECM Power Source Circuit |
| Crankshaft position sensor | Refer to INSPECTION PROCEDURE | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Fuel suction with pump and gauge tube assembly | Refer to INSPECTION - Step 1 | |
| Fuel injector circuit | Refer to Fuel Injector Circuit | |
| Valve timing | Refer to PROCEDURE - Step 4 | |
| VC output circuit (ECM 5 V output) | Refer to VC Output Circuit | |
| Camshaft position sensor (for intake camshaft) |
Refer to INSPECTION PROCEDURE | |
| Camshaft position sensor (for exhaust camshaft) |
Refer to INSPECTION PROCEDURE | |
| Starter signal circuit | Refer to Starter Signal Circuit | |
| Engine immobiliser system (w/ engine immobiliser system) | Refer to REGISTRATION | |
| ECM | Refer to TERMINALS OF ECM | |
| Engine cranks normally but difficult to start | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Fuel suction with pump and gauge tube assembly | Refer to INSPECTION | |
| Fuel injector circuit | Refer to Fuel Injector Circuit | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Starter signal circuit | Refer to Starter Signal Circuit | |
| Engine coolant temperature sensor | Refer to INSPECTION | |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Spark plug | Refer to ON-VEHICLE INSPECTION - Step 2 | |
| Throttle with motor body assembly | Refer to ON-VEHICLE INSPECTION | |
| Compression | Refer to ON-VEHICLE INSPECTION - Step 9 | |
| Incomplete intermittent combustion occurs (Does not start) | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Fuel suction with pump and gauge tube assembly | Refer to INSPECTION | |
| Fuel line | Refer to ON-VEHICLE INSPECTION | |
| Ignition circuit | Refer to INSPECTION PROCEDURE | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector circuit | Refer to Fuel Injector Circuit | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Starter signal circuit | Refer to Starter Signal Circuit | |
| Crankshaft position sensor | Refer to INSPECTION PROCEDURE | |
| Camshaft position sensor (for intake camshaft) |
Refer to INSPECTION PROCEDURE | |
| Camshaft position sensor (for exhaust camshaft) |
Refer to INSPECTION PROCEDURE | |
| Engine immobiliser system (w/ engine immobiliser system) | Refer to REGISTRATION | |
| Valve timing | Refer to PROCEDURE - Step 4 | |
| High engine idle speed | Throttle with motor body assembly | Refer to ON-VEHICLE INSPECTION |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| A/C signal circuit for automatic air conditioning system | Refer to PROBLEM SYMPTOMS TABLE | |
| A/C signal circuit for manual air conditioning system | Refer to PROBLEM SYMPTOMS TABLE | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Engine coolant temperature sensor | Refer to INSPECTION | |
| PCV valve and hose | Refer to ON-VEHICLE INSPECTION | |
| ACIS control circuit | Refer to ACIS Control Circuit | |
| Low engine idle speed (Poor idling) | Throttle with motor body assembly | Refer to ON-VEHICLE INSPECTION |
| A/C signal circuit for automatic air conditioning system | Refer to PROBLEM SYMPTOMS TABLE | |
| A/C signal circuit for manual air conditioning system | Refer to PROBLEM SYMPTOMS TABLE | |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Fuel suction with pump and gauge tube assembly | Refer to INSPECTION | |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| PCV valve and hose | Refer to ON-VEHICLE INSPECTION | |
| ACIS control circuit | Refer to ACIS Control Circuit | |
| Rough idling | Compression | Refer to ON-VEHICLE INSPECTION - Step 9 |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Spark plug | Refer to ON-VEHICLE INSPECTION - Step 2 | |
| Fuel injector circuit | Refer to Fuel Injector Circuit | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Fuel suction with pump and gauge tube assembly | Refer to INSPECTION | |
| Fuel line | Refer to ON-VEHICLE INSPECTION | |
| Throttle with motor body assembly | Refer to ON-VEHICLE INSPECTION | |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| PCV valve and hose | Refer to ON-VEHICLE INSPECTION | |
| Air fuel ratio sensor | Refer to INSPECTION | |
| Heated oxygen sensor | Refer to INSPECTION | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Knock sensor | Refer to INSPECTION - Step 1 | |
| ACIS control circuit | Refer to ACIS Control Circuit | |
| Tumble Control Valve (TCV) | Refer to ON-VEHICLE INSPECTION - Step 3 | |
| External part malfunction (Increase in load: A/C system, CVT system, etc.) | - | |
| Hunting (Poor idling) | Throttle with motor body assembly | Refer to ON-VEHICLE INSPECTION |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| PCV valve and hose | Refer to ON-VEHICLE INSPECTION | |
| Air fuel ratio sensor | Refer to INSPECTION | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| ACIS control circuit | Refer to ACIS Control Circuit | |
| Tumble Control Valve (TCV) | Refer to ON-VEHICLE INSPECTION - Step 3 | |
| Hesitation/poor acceleration | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Fuel suction with pump and gauge tube assembly | Refer to INSPECTION | |
| Fuel line | Refer to ON-VEHICLE INSPECTION | |
| Spark plug | Refer to ON-VEHICLE INSPECTION - Step 2 | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector circuit | Refer to Fuel Injector Circuit | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Throttle with motor body assembly | Refer to ON-VEHICLE INSPECTION | |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| Valve timing | Refer to PROCEDURE - Step 4 | |
| Compression | Refer to ON-VEHICLE INSPECTION - Step 9 | |
| Brake override system | Refer to Brake Override System | |
| Surging (Poor driveability) | Spark plug | Refer to ON-VEHICLE INSPECTION - Step 2 |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Fuel suction with pump and gauge tube assembly | Refer to INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector circuit | Refer to Fuel Injector Circuit | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Variable Valve Timing (VVT) system | Refer to ON-VEHICLE INSPECTION | |
| Compression | Refer to ON-VEHICLE INSPECTION - Step 9 | |
| Engine stalls soon after starting | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Fuel suction with pump and gauge tube assembly | Refer to INSPECTION | |
| Spark plug | Refer to ON-VEHICLE INSPECTION - Step 2 | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector circuit | Refer to Fuel Injector Circuit | |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Mass air flow meter | Refer to ON-VEHICLE INSPECTION | |
| Variable Valve Timing (VVT) system | Refer to ON-VEHICLE INSPECTION | |
| Throttle with motor body assembly | Refer to ON-VEHICLE INSPECTION | |
| Intake system | Refer to ON-VEHICLE INSPECTION | |
| PCV valve and hose | Refer to ON-VEHICLE INSPECTION | |
| Compression | Refer to ON-VEHICLE INSPECTION - Step 9 | |
| Engine stalls only during A/C operation | A/C signal circuit for automatic air conditioning system | Refer to PROBLEM SYMPTOMS TABLE |
| A/C signal circuit for manual air conditioning system | Refer to PROBLEM SYMPTOMS TABLE | |
| ECM | Refer to TERMINALS OF ECM | |
| Unable/difficult to refuel | Fuel system (canister, canister pump module, 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.