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 .
DIAGNOSTIC INFORMATION AND PROCEDURES REFERENCE CHART
| 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 | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION | |
| Faulty APP sensor assembly | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY INSPECTION | |
| Faulty ECT sensor or MAF sensor | ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION or MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) 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 BEARINGS INSPECTION | |
| Worn crankshaft journal | MAIN BEARINGS INSPECTION | |
| Loose bearing cap bolts | MAIN BEARINGS, CRANKSHAFT AND CYLINDER BLOCK REMOVAL AND INSTALLATION | |
| Excessive crankshaft thrust play | MAIN BEARINGS 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 SYSTEM SYMPTOM DIAGNOSIS | |
| Blown cylinder head gasket | CYLINDER HEAD INSPECTION | |
| Air mixed in cooling system | COOLING SYSTEM FLUSHING | |
| 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 | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY INSPECTION or MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION | |
| Faulty throttle body assembly | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION | |
| Faulty APP sensor assembly | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY 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 SYSTEM SYMPTOM DIAGNOSIS | |
| Thermostat out of order | THERMOSTAT INSPECTION | |
| Improper tire pressure | TIRES DESCRIPTION | |
| Fuel pressure out of specification | FUEL PRESSURE CHECK | |
| Camshaft position control (VVT) system out of order | OCV (OIL 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 | ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION or MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION | |
| Faulty throttle body assembly | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION | |
| Faulty APP sensor assembly | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY 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 | MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION | |
| Faulty fuel injector | FUEL INJECTOR CIRCUIT CHECK | |
| Faulty ECM | INSPECTION OF ECM AND ITS CIRCUITS | |
| Faulty throttle body assembly | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION | |
| Faulty APP sensor assembly | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY 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 , ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION or MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION | |
| Faulty fuel injector(s) | FUEL PRESSURE 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 | ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION or MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION | |
| Faulty throttle body assembly | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION | |
| Faulty APP sensor assembly | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY 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 SYSTEM SYMPTOM DIAGNOSIS | |
| Low compression | COMPRESSION CHECK | |
| Camshaft position control (VVT) system out of order | OCV (OIL CONTROL VALVE) INSPECTION | |
| Faulty IMT valve actuator | IMT VALVE ACTUATOR INSPECTION | |
| Improper engine idling or engine fails to idle | Faulty spark plug | SPARK PLUG INSPECTION |
| Faulty ignition coil with ignitor | IGNITION COIL ASSEMBLY REMOVAL AND INSTALLATION | |
| 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 | ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION or MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION | |
| Faulty throttle body assembly | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION | |
| Faulty APP sensor assembly | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY 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) | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION , ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION or MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION | |
| Faulty throttle body assembly | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION | |
| Faulty APP sensor assembly | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY 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) | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION , ENGINE COOLANT TEMPERATURE (ECT) SENSOR INSPECTION or MASS AIR FLOW (MAF) & INTAKE AIR TEMPERATURE (IAT) SENSOR INSPECTION | |
| Faulty throttle body assembly | ELECTRIC THROTTLE BODY ASSEMBLY ON-VEHICLE INSPECTION | |
| Faulty APP sensor assembly | ACCELERATOR PEDAL POSITION (APP) SENSOR ASSEMBLY 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 |