Engine Symptom Diagnosis
Perform troubleshooting referring to the following when ECM has detected no DTC and no abnormality has been found in VISUAL INSPECTION and ENGINE BASIC INSPECTION .
| Condition | Possible Cause | Action |
|---|---|---|
| Hard starting (Engine can be cranked) | Faulty spark plug | Spark Plug Inspection |
| Faulty ignition coil | Ignition Coil Assembly Inspection | |
| Dirty or clogged fuel hose or pipe | Fuel Pressure Check | |
| Malfunctioning fuel pump | Fuel Pressure Check | |
| Air drawn in through intake manifold gasket or throttle body gasket | Check air intake system . | |
| Faulty throttle body assembly | Throttle Body Assembly On-Vehicle Inspection | |
| Faulty APP sensor assembly | APP (Accelerator Pedal Position) Sensor Inspection | |
| Faulty ECT sensor or MAF sensor | ECT (Engine Coolant Temperature) Sensor Inspection or MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty ECM | Inspection of ECM and Its Circuits . | |
| Low compression | Compression Check | |
| Poor spark plug tightening or faulty gasket | Spark Plug Removal and Installation | |
| Compression leak from valve seat | Valve and Valve Guide Inspection | |
| Sticky valve stem | Valve and Valve Guide Inspection | |
| Weak or damaged valve springs | Valve Spring Inspection | |
| Compression leak at cylinder head gasket | Cylinder Head Inspection | |
| Sticking or damaged piston ring | Cylinder, Piston and Piston Ring Inspection | |
| Worn piston, piston ring or cylinder | Cylinder, Piston and Piston Ring Inspection | |
| Malfunctioning PCV valve | PCV Valve Inspection | |
| Camshaft position control (VVT) system out of order | OCV (Oil Control Valve) Inspection | |
| Low oil pressure | Improper oil viscosity | Engine Oil and Filter Change |
| Malfunctioning oil pressure switch | Oil Pressure Switch On-Vehicle Inspection | |
| Clogged oil strainer | Check oil strainer for clog . | |
| Functional deterioration of oil pump | Oil Pump Inspection | |
| Worn oil pump relief valve | Oil Pump Inspection | |
| Excessive clearance in various sliding parts | - | |
| Engine noise - Valve noise
NOTE:
Before checking mechanical noise, make sure that:
|
Improper valve clearance | Camshaft and Tappet Inspection |
| Worn valve stem and guide | Valve and Valve Guide Inspection | |
| Weak or broken valve spring | Valve Spring Inspection | |
| Warped or bent valve | Valve and Valve Guide Inspection | |
| Engine noise - Piston, piston ring and cylinder noise
NOTE:
Before checking mechanical noise, make sure that:
|
Worn piston, piston ring and cylinder bore | Cylinder, Piston and Piston Ring Inspection |
| Engine noise - Connecting rod noise
NOTE:
Before checking mechanical noise, make sure that:
|
Worn piston, piston ring and cylinder bore | Cylinder, Piston and Piston Ring Inspection |
| Worn connecting rod bearing | Cylinder, Piston and Piston Ring Inspection | |
| Worn crank pin | Cylinder, Piston and Piston Ring Inspection | |
| Loose connecting rod bolts | Piston, Piston Ring and Connecting Rod Removal and Installation | |
| Low oil pressure | Condition "Low oil pressure" | |
| Engine noise - Crankshaft noise
NOTE:
Before checking mechanical noise, make sure that:
|
Low oil pressure | Condition "Low oil pressure" |
| Worn main bearing | Main Bearing Inspection | |
| Worn crankshaft journal | Main Bearing Inspection | |
| Loose bearing cap bolts | Main Bearing, Crankshaft and Cylinder Block Removal and Installation | |
| Excessive crankshaft thrust play | Main Bearing Inspection | |
| Engine overheating | Inoperative thermostat | Thermostat Inspection |
| Poor water pump performance | Water Pump Inspection | |
| Clogged or leaky radiator | Radiator On-Vehicle Inspection and Cleaning | |
| Improper engine oil grade | Engine Oil and Filter Change | |
| Clogged oil filter or oil strainer | Oil Pressure Check | |
| Poor oil pump performance | Oil Pressure Check | |
| Faulty radiator cooling fan control system | Radiator Cooling Fan Control System Check | |
| Dragging brakes | Brakes Symptom Diagnosis | |
| Slipping clutch (M/T model) | Clutch (Hydraulic Type) Symptom Diagnosis | |
| Blown cylinder head gasket | Cylinder Head Inspection | |
| Air mixed in cooling system | Cooling System Refilling | |
| Poor fuel mileage | Faulty spark plug (improper gap, heavy deposits and burned electrodes, etc.) | Spark Plug Inspection |
| High idle speed | Condition "Improper engine idling or engine fails to idle" | |
| Poor performance of ECT sensor or MAF sensor | APP (Accelerator Pedal Position) Sensor Inspection or MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty throttle body assembly | Throttle Body Assembly On-Vehicle Inspection | |
| Faulty APP sensor assembly | APP (Accelerator Pedal Position) Sensor Inspection | |
| Faulty fuel injector(s) | Fuel Injector Circuit Check | |
| Faulty ECM | Inspection of ECM and Its Circuits | |
| Low compression | Compression Check | |
| Poor valve seating | Valve and Valve Guide Inspection | |
| Dragging brakes | Brakes Symptom Diagnosis | |
| Slipping clutch (M/T model) | Clutch (Hydraulic Type) Symptom Diagnosis | |
| Thermostat out of order | Thermostat Inspection | |
| Improper tire pressure | Tire Description | |
| Fuel pressure out of specification | Fuel Pressure Check | |
| Camshaft position control (VVT) system out of order | OCV (Oil Control Valve) Inspection | |
| Faulty IMRC valve | IMRC (Intake Manifold Runner Control) Valve Inspection | |
| Excessive engine oil consumption - Oil leakage | Blown cylinder head gasket | Cylinder Head Inspection |
| Leaky camshaft oil seals | Camshaft and Tappet Inspection | |
| Excessive engine oil consumption - Oil entering combustion chamber | Sticky piston ring | Cylinder, Piston and Piston Ring Inspection |
| Worn piston and cylinder | Cylinder, Piston and Piston Ring Inspection | |
| Worn piston ring groove and ring | Cylinder, Piston and Piston Ring Inspection | |
| Improper location of piston ring gap | Cylinder, Piston and Piston Ring Inspection | |
| Worn or damaged valve stem seal | Valve and Valve Guide Inspection | |
| Worn valve stem | Valve and Valve Guide Inspection | |
| Engine hesitates - Momentary lack of response as accelerator is depressed. Can occur at all vehicle speeds. Usually most severe when first trying to make vehicle move, such as from a stop sign | Spark plug faulty or plug gap out of adjustment | Spark Plug Inspection |
| Fuel pressure out of specification | Fuel Pressure Check | |
| Poor performance of ECT sensor or MAF sensor | ECT (Engine Coolant Temperature) Sensor Inspection or MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty throttle body assembly | Throttle Body Assembly On-Vehicle Inspection | |
| Faulty APP sensor assembly | APP (Accelerator Pedal Position) Sensor Inspection | |
| Faulty fuel injector | Fuel Injector Circuit Check | |
| Faulty ECM | Inspection of ECM and Its Circuits | |
| Engine overheating | Condition "Engine overheating" | |
| Low compression | Compression Check | |
| Surge - Engine power variation under steady throttle or cruise. Feels like vehicle speeds up and down with no change in accelerator pedal | Faulty spark plug (excess carbon deposits, improper gap, burned electrodes, etc.) | Spark Plug Inspection |
| Variable fuel pressure | Fuel Pressure Check | |
| Kinky or damaged fuel hose and lines | Fuel Pressure Check | |
| Faulty fuel pump (clogged fuel filter) | Fuel Pump and Its Circuit Check | |
| Poor performance of MAF sensor | MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty fuel injector | Fuel Injector Circuit Check | |
| Faulty ECM | Inspection of ECM and Its Circuits | |
| Faulty throttle body assembly | Throttle Body Assembly On-Vehicle Inspection | |
| Faulty APP sensor assembly | APP (Accelerator Pedal Position) Sensor Inspection | |
| Camshaft position control (VVT) system out of order | OCV (Oil Control Valve) Inspection | |
| Excessive detonation - Engine makes continuously sharp metallic knocks that change with throttle opening. Sounds like popcorn popping | Faulty spark plug | Spark Plug Inspection |
| Engine overheating | Condition "Engine overheating" | |
| Clogged fuel filter (faulty fuel pump) or fuel lines | Fuel Pressure Check or Fuel Pump and Its Circuit Check | |
| Air drawn in through intake manifold or throttle body gasket | Check air intake system . | |
| Poor performance of knock sensor, ECT sensor or MAF sensor | Knock Sensor Inspection, ECT (Engine Coolant Temperature) Sensor Inspection or MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty fuel injector(s) | Fuel Injector Circuit Check | |
| Faulty ECM | Inspection of ECM and Its Circuits | |
| Excessive combustion chamber deposits | Cylinder Head Inspection and Cylinder, Piston and Piston Ring Inspection | |
Fuel pressure out of specification
|
Fuel Pressure Check | |
| Camshaft position control (VVT) system out of order | OCV (Oil Control Valve) Inspection | |
| Engine has no power | Faulty spark plug | Spark Plug Inspection |
| Faulty ignition coil with ignitor | Ignition Coil Assembly Inspection | |
| Faulty knock sensor | Knock Sensor Inspection | |
| Clogged fuel hose or pipe | Fuel Pressure Check | |
| Malfunctioning fuel pump | Fuel Pump and Its Circuit Check | |
| Air drawn in through intake manifold gasket or throttle body gasket | Check air intake system . | |
| Engine overheating | Condition "Engine overheating" | |
| Poor performance of ECT sensor or MAF sensor | ECT (Engine Coolant Temperature) Sensor Inspection or MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty throttle body assembly | Throttle Body Assembly On-Vehicle Inspection | |
| Faulty APP sensor assembly | APP (Accelerator Pedal Position) Sensor Inspection | |
| Faulty fuel injector(s) | Fuel Injector Circuit Check | |
| Faulty ECM | Inspection of ECM and Its Circuits | |
| Dragging brakes | Brakes Symptom Diagnosis | |
| Slipping clutch (M/T model) | Clutch (Hydraulic Type) Symptom Diagnosis | |
| Low compression | Compression Check | |
| Camshaft position control (VVT) system out of order | OCV (Oil Control Valve) Inspection | |
| Faulty IMT vacuum solenoid valve | IMT (Intake Manifold Tuning) Vacuum Solenoid Valve On-Vehicle Inspection | |
| Faulty IMRC valve | IMRC (Intake Manifold Runner Control) Valve Inspection | |
| Improper engine idling or engine fails to idle | Faulty spark plug | Spark Plug Inspection |
| Faulty ignition coil with ignitor | Ignition Coil Assembly Inspection | |
| Fuel pressure out of specification | Fuel Pressure Check | |
| Leaky manifold, throttle body, or cylinder head gasket | Check air intake system . | |
| Faulty evaporative emission control system | EVAP Canister Purge System Inspection | |
| Faulty fuel injector(s) | Fuel Injector Circuit Check | |
| Poor performance of ECT sensor or MAF sensor | ECT (Engine Coolant Temperature) Sensor Inspection or MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty throttle body assembly | Throttle Body Assembly On-Vehicle Inspection | |
| Faulty APP sensor assembly | APP (Accelerator Pedal Position) Sensor Inspection | |
| Faulty ECM | Inspection of ECM and Its Circuits | |
| Loose connection or disconnection of vacuum hoses | Check connection or disconnection of vacuum . | |
| Malfunctioning PCV valve | PCV Valve Inspection | |
| Engine overheating | Condition "Engine overheating" | |
| Low compression | Compression Check | |
| Faulty generator and/or its circuit | Generator Test | |
| Camshaft position control (VVT) system out of order | OCV (Oil Control Valve) Inspection | |
| Excessive hydrocarbon (HC) or carbon monoxide (CO) emission | Faulty spark plug | Spark Plug Inspection |
| Faulty ignition coil with ignitor | Ignition Coil Assembly Inspection | |
| Low compression | Compression Check | |
| Lead contamination of three way catalytic converter | Check for absence of filler neck restrictor . | |
| Faulty evaporative emission control system | EVAP Canister Purge System Inspection | |
| Fuel pressure out of specification | Fuel Pressure Check | |
| Closed loop system (A/F feedback compensation) fails (faulty TP sensor, poor performance of ECT sensor or MAF sensor) | Throttle Body Assembly On-Vehicle Inspection, ECT (Engine Coolant Temperature) Sensor Inspection or MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty throttle body assembly | Throttle Body Assembly On-Vehicle Inspection , | |
| Faulty APP sensor assembly | APP (Accelerator Pedal Position) Sensor Inspection | |
| Faulty injector(s) | Fuel Injector Circuit Check | |
| Faulty ECM | Inspection of ECM and Its Circuits | |
| Engine not at normal operating temperature | - | |
| Clogged air cleaner | Air Cleaner Filter Inspection and Cleaning | |
| Vacuum leak | Engine Vacuum Check | |
| Camshaft position control (VVT) system out of order | OCV (Oil Control Valve) Inspection | |
| Excessive nitrogen oxides (NOx) emission | Improper ignition timing | Ignition Timing Inspection |
| Lead contamination of catalytic converter | Check for absence of filler neck restrictor . | |
| Fuel pressure out of specification | Fuel Pressure Check | |
| Closed loop system (A/F feedback compensation) fails (faulty TP sensor, poor performance of ECT sensor or MAF sensor) | Throttle Body Assembly On-Vehicle Inspection, ECT (Engine Coolant Temperature) Sensor Inspection or MAF (Mass Air Flow) and IAT (Intake Air Temperature) Sensor Inspection | |
| Faulty throttle body assembly | Throttle Body Assembly On-Vehicle Inspection | |
| Faulty APP sensor assembly | APP (Accelerator Pedal Position) Sensor Inspection | |
| Faulty injector(s) | Fuel Injector Circuit Check | |
| Faulty ECM | Inspection of ECM and Its Circuits | |
| Camshaft position control (VVT) system out of order | OCV (Oil Control Valve) Inspection |