Symptoms and causes: Inspection
WARNING: This page is about a different car, the 2022 Subaru WRX. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
Check the control operation history. Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>WORK SUPPORT>OPERATION
NOTE:
The "RANK" shown in the chart shows the possibilities of the cause of trouble in order from "Very often" to "Rarely".
A - Very often
B - Sometimes
C - Rarely
| Symptoms | Problem parts etc. | Possible cause | RANK |
|---|---|---|---|
| 1. Engine does not start. | |||
| 1) Starter does not turn. | Starter | Defective battery-to-starter harness | B |
| Defective starter switch | C | ||
| Defective relay | C | ||
| Defective inhibitor switch | C | ||
| Defective clutch start switch | C | ||
| Defective starter | B | ||
| Battery | Improper connection of terminal | A | |
| Run-down battery | A | ||
| Defective charging system | B | ||
| Friction | Seizure of crankshaft and connecting rod bearing | C | |
| Seized camshaft | C | ||
| Seized or stuck piston and cylinder | C | ||
| Immobilizer system Ref. to IMMOBILIZER (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE | A | ||
| 2) Initial combustion does not occur. | Starter | Defective starter | C |
| Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | ||
| Fuel line | Defective fuel pump and relay | A | |
| Clogged fuel line | C | ||
| Lack of fuel or insufficient fuel | B | ||
| Timing chain | Trouble | B | |
| Defective timing | B | ||
| Compression | Incorrect cam clearance | C | |
| Loosened spark plug or defective gasket | C | ||
| Loosened cylinder head bolt or defective cylinder head gasket | C | ||
| Improper valve sealing | C | ||
| Defective valve stem | C | ||
| Worn or broken valve spring | B | ||
| Worn or stuck piston rings, cylinder liner and piston | C | ||
| Incorrect valve timing | B | ||
| Improper engine oil (low viscosity) | B | ||
| 3) Initial combustion occurs. | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Defective intake manifold gasket | B | |
| Defective throttle body gasket | B | ||
| Fuel line | Defective fuel pump and relay | C | |
| Clogged fuel line | C | ||
| Lack of fuel or insufficient fuel | B | ||
| Timing chain | Trouble | B | |
| Defective timing | B | ||
| Compression | Incorrect cam clearance | C | |
| Loosened spark plug or defective gasket | C | ||
| Loosened cylinder head bolt or defective cylinder head gasket | C | ||
| Improper valve sealing | C | ||
| Defective valve stem | C | ||
| Worn or broken valve spring | B | ||
| Worn or stuck piston rings, cylinder liner and piston | C | ||
| Incorrect valve timing | B | ||
| Improper engine oil (low viscosity) | B | ||
| 4) Engine stalls after initial combustion. | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Loosened or cracked intake duct | B | |
| Loosened or cracked PCV hose | C | ||
| Loosened or cracked vacuum hose | C | ||
| Defective intake manifold gasket | B | ||
| Defective throttle body gasket | B | ||
| Dirty air cleaner element | C | ||
| Defective electronic air by-pass valve | C | ||
| Fuel line | Clogged fuel line | C | |
| Lack of fuel or insufficient fuel | B | ||
| Timing chain | Trouble | B | |
| Defective timing | B | ||
| Compression | Incorrect cam clearance | C | |
| Loosened spark plug or defective gasket | C | ||
| Loosened cylinder head bolt or defective cylinder head gasket | C | ||
| Improper valve sealing | C | ||
| Defective valve stem | C | ||
| Worn or broken valve spring | B | ||
| Worn or stuck piston rings, cylinder and piston | C | ||
| Incorrect valve timing | B | ||
| Improper engine oil (low viscosity) | B | ||
| 2. Rough idle and engine stall | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Loosened or cracked intake duct | A | |
| Loosened or cracked PCV hose | A | ||
| Loosened or cracked vacuum hose | A | ||
| Defective intake manifold gasket | B | ||
| Defective throttle body gasket | B | ||
| Defective PCV valve | C | ||
| Loosened oil filler cap | B | ||
| Dirty air cleaner element | C | ||
| Defective electronic air by-pass valve | C | ||
| Fuel line | Defective fuel pump and relay | C | |
| Clogged fuel line | C | ||
| Lack of fuel or insufficient fuel | B | ||
| Timing chain | Defective timing | C | |
| Compression | Incorrect cam clearance | B | |
| Loosened spark plug or defective gasket | B | ||
| Loosened cylinder head bolt or defective cylinder head gasket | B | ||
| Improper valve sealing | B | ||
| Defective valve stem | C | ||
| Worn or broken valve spring | B | ||
| Worn or stuck piston rings, cylinder and piston | B | ||
| Incorrect valve timing | A | ||
| Improper engine oil (low viscosity) | B | ||
| Lubrication system | Incorrect oil pressure | B | |
| Defective rocker cover gasket | C | ||
| Cooling system | Over-heating | C | |
| Other | Evaporative emission control system malfunction | A | |
| Stuck or damaged throttle valve | B | ||
| 3. Low output, hesitation and poor acceleration | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Loosened or cracked intake duct | A | |
| Loosened or cracked PCV hose | A | ||
| Loosened or cracked vacuum hose | B | ||
| Defective intake manifold gasket | B | ||
| Defective throttle body gasket | B | ||
| Defective PCV valve | B | ||
| Loosened oil filler cap | B | ||
| Dirty air cleaner element | A | ||
| Defective electronic air by-pass valve | C | ||
| Fuel line | Defective fuel pump and relay | B | |
| Clogged fuel line | B | ||
| Lack of fuel or insufficient fuel | C | ||
| Timing chain | Defective timing | B | |
| Compression | Incorrect cam clearance | B | |
| Loosened spark plug or defective gasket | B | ||
| Loosened cylinder head bolt or defective cylinder head gasket | B | ||
| Improper valve sealing | B | ||
| Defective valve stem | C | ||
| Worn or broken valve spring | B | ||
| Worn or stuck piston rings, cylinder and piston | C | ||
| Incorrect valve timing | A | ||
| Improper engine oil (low viscosity) | B | ||
| Lubrication system | Incorrect oil pressure | B | |
| Cooling system | Over-heating | C | |
| Over-cooling | C | ||
| Other | Evaporative emission control system malfunction | A | |
| 4. Surging | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Loosened or cracked intake duct | A | |
| Loosened or cracked PCV hose | A | ||
| Loosened or cracked vacuum hose | A | ||
| Defective intake manifold gasket | B | ||
| Defective throttle body gasket | B | ||
| Defective PCV valve | B | ||
| Loosened oil filler cap | B | ||
| Dirty air cleaner element | B | ||
| Defective electronic air by-pass valve | C | ||
| Fuel line | Defective fuel pump and relay | B | |
| Clogged fuel line | B | ||
| Lack of fuel or insufficient fuel | C | ||
| Timing chain | Defective timing | B | |
| Compression | Incorrect cam clearance | B | |
| Loosened spark plug or defective gasket | C | ||
| Loosened cylinder head bolt or defective cylinder head gasket | C | ||
| Improper valve sealing | C | ||
| Defective valve stem | C | ||
| Worn or broken valve spring | C | ||
| Worn or stuck piston rings, cylinder and piston | C | ||
| Incorrect valve timing | A | ||
| Improper engine oil (low viscosity) | B | ||
| Cooling system | Over-heating | B | |
| Other | Evaporative emission control system malfunction | C | |
| 5. Engine does not return to idle. | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Loosened or cracked vacuum hose | A | |
| Other | Stuck or damaged throttle valve | A | |
| 6. Dieseling (run-on) | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Cooling system | Over-heating | B | |
| Other | Evaporative emission control system malfunction | B | |
| 7. After burning in exhaust system | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Loosened or cracked intake duct | C | |
| Loosened or cracked PCV hose | C | ||
| Loosened or cracked vacuum hose | B | ||
| Defective PCV valve | B | ||
| Loosened oil filler cap | C | ||
| Defective electronic air by-pass valve | C | ||
| Timing chain | Defective timing | B | |
| Compression | Incorrect cam clearance | B | |
| Loosened spark plug or defective gasket | C | ||
| Loosened cylinder head bolt or defective cylinder head gasket | C | ||
| Improper valve sealing | B | ||
| Defective valve stem | C | ||
| Worn or broken valve spring | C | ||
| Worn or stuck piston rings, cylinder and piston | C | ||
| Incorrect valve timing | A | ||
| Lubrication system | Incorrect oil pressure | C | |
| Cooling system | Over-cooling | C | |
| Other | Evaporative emission control system malfunction | C | |
| 8. Knocking | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Loosened oil filler cap | B | |
| Timing chain | Defective timing | B | |
| Compression | Incorrect cam clearance | C | |
| Incorrect valve timing | B | ||
| Cooling system | Over-heating | A | |
| 9. Excessive engine oil consumption | Intake system | Loosened or cracked PCV hose | A |
| Defective PCV valve | B | ||
| Loosened oil filler cap | C | ||
| Compression | Defective valve stem | A | |
| Worn or stuck piston rings, cylinder and piston | A | ||
| Lubrication system | Loosened chain cover attaching bolts and defective gasket | B | |
| Defective oil filter gasket | B | ||
| Defective crankshaft oil seal | B | ||
| Defective rocker cover gasket | B | ||
| Loosened oil drain plug or defective gasket | B | ||
| Loosened oil pan mounting bolt or defective oil pan | B | ||
| 10. Excessive fuel consumption | Engine control system Ref. to ENGINE (DIAGNOSTICS) (H4DOTC)>BASIC DIAGNOSTIC PROCEDURE | A | |
| Intake system | Dirty air cleaner element | A | |
| Timing chain | Defective timing | B | |
| Compression | Incorrect cam clearance | B | |
| Loosened spark plug or defective gasket | C | ||
| Loosened cylinder head bolt or defective cylinder gasket | C | ||
| Improper valve sealing | B | ||
| Defective valve stem | C | ||
| Worn or broken valve spring | C | ||
| Worn or stuck piston rings, cylinder and piston | B | ||
| Incorrect valve timing | B | ||
| Lubrication system | Incorrect oil pressure | C | |
| Cooling system | Over-cooling | C | |