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 Highlander Limited, FWDFACTORY OEM SERVICE PROCEDURE
Problem Symptoms Table
HINT:
When a malfunction is not confirmed by a DTC (Diagnostic Trouble Code) check and the cause of problem cannot be identified through a basic inspection, troubleshoot according to the priority order indicated in the table below.
SFI SYSTEM:
| Symptom | Suspected Area | See |
|---|---|---|
| Engine does not crank (does not start) | Battery | Refer to ON-VEHICLE INSPECTION - Step 1 |
| Immobilizer system (w/ Smart Key System) | Refer to HOW TO PROCEED WITH TROUBLESHOOTING | |
| VC output circuit (ECM 5 V circuit) | Refer to VC Output Circuit | |
| Starter | Refer to INSPECTION | |
| ST relay | Refer to ON-VEHICLE INSPECTION | |
| Cranking holding function circuit (w/ Smart Key System) | Refer to Cranking Holding Function Circuit | |
| Starter signal circuit (w/o Smart Key System) | Refer to Starter Signal Circuit | |
| No initial combustion (does not start) | ECM power source circuit | Refer to ECM Power Source Circuit |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Fuel injector | Refer to INSPECTION | |
| ECM | - | |
| Difficult to start (engine cranks normally) | Electronic throttle control system | Refer to DTC P2102: Throttle Actuator Control Motor Circuit Low; DTC P2103: Throttle Actuator Control Motor Circuit High |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Spark plug | Refer to ON-VEHICLE INSPECTION | |
| Compression | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector | Refer to INSPECTION | |
| Difficult to start with cold engine | Electronic throttle control system | Refer to DTC P2102: Throttle Actuator Control Motor Circuit Low; DTC P2103: Throttle Actuator Control Motor Circuit High |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Spark plug | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector | Refer to INSPECTION | |
| Engine coolant temperature sensor | Refer to INSPECTION | |
| Difficult to start with hot engine | Electronic throttle control system | Refer to DTC P2102: Throttle Actuator Control Motor Circuit Low; DTC P2103: Throttle Actuator Control Motor Circuit High |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Spark plug | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector | Refer to INSPECTION | |
| Engine coolant temperature sensor | Refer to INSPECTION | |
| High engine idle speed (poor idling) | Electronic throttle control system | Refer to DTC P2102: Throttle Actuator Control Motor Circuit Low; DTC P2103: Throttle Actuator Control Motor Circuit High |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| A/C signal circuit (Compressor circuit) | - | |
| Acoustic control induction system | Refer to ACIS Control Circuit | |
| PCV hose | Refer to PARTS LOCATION | |
| ECM | - | |
| Low engine idle speed (poor idling) | Electronic throttle control system | Refer to DTC P2102: Throttle Actuator Control Motor Circuit Low; DTC P2103: Throttle Actuator Control Motor Circuit High |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| A/C signal circuit (Compressor circuit) | - | |
| Acoustic control induction system | Refer to ACIS Control Circuit | |
| PCV hose | Refer to PARTS LOCATION | |
| Fuel injector | Refer to INSPECTION | |
| ECM | - | |
| Rough idling (poor idling) | Electronic throttle control system | Refer to DTC P2102: Throttle Actuator Control Motor Circuit Low; DTC P2103: Throttle Actuator Control Motor Circuit High |
| Fuel injector | Refer to INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Compression | Refer to ON-VEHICLE INSPECTION | |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Spark plug | Refer to ON-VEHICLE INSPECTION | |
| Acoustic control induction system | Refer to ACIS Control Circuit | |
| PCV hose | Refer to PARTS LOCATION | |
| Hunting (poor idling) | Electronic throttle control system | Refer to DTC P2102: Throttle Actuator Control Motor Circuit Low; DTC P2103: Throttle Actuator Control Motor Circuit High |
| ECM power source circuit | Refer to ECM Power Source Circuit | |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Spark plug | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector | Refer to INSPECTION | |
| Acoustic control induction system | Refer to ACIS Control Circuit | |
| PCV hose | Refer to PARTS LOCATION | |
| Hesitation/Poor acceleration (poor driveability) | Fuel injector | Refer to INSPECTION |
| Fuel pump control circuit | Refer to Fuel Pump Control Circuit | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Spark plug | Refer to ON-VEHICLE INSPECTION | |
| Air intake control system | Refer to Air Intake Control Circuit | |
| A/T faulty (U151E) | Refer to HOW TO PROCEED WITH TROUBLESHOOTING | |
| A/T faulty (U151F) | Refer to HOW TO PROCEED WITH TROUBLESHOOTING | |
| Brake override system | Refer to Brake Override System | |
| Surging (poor driveability) | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Spark plug | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector | Refer to INSPECTION | |
| Engine stalls soon after starting | Fuel pump control circuit | Refer to Fuel Pump Control Circuit |
| Electronic throttle control system | Refer to DTC P2102: Throttle Actuator Control Motor Circuit Low; DTC P2103: Throttle Actuator Control Motor Circuit High | |
| Crankshaft position sensor | Refer to INSPECTION | |
| Spark plug | Refer to ON-VEHICLE INSPECTION | |
| Ignition system | Refer to ON-VEHICLE INSPECTION | |
| Fuel injector | Refer to INSPECTION | |
| Engine stalls during A/C operation | A/C signal circuit (Compressor circuit) | - |
| ECM | - | |
| Unable/difficult to refuel | Refueling valve (canister) | - |
| Engine vibrates frequently when idling (Active Control) | Active control engine mount circuit | Refer to Active Control Engine Mount System |
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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