Top 20 Engine Service Codes In Our Shop for 2021
As we wrap up 2021, We have taken vehicle data from diagnostics throughout the year. These are the 20 most common check engine codes diagnosed and fixed by our technicians. Keep reading to discover symptoms associated with these OBD codes and the most common causes.
#1: P0300
Ranking #1 on our list, at least 47% of our customer’s vehicles scanned received this common engine code which indicates that one or more cylinders are experiencing misfires.Â
Symptoms:
- Check engine light is on or flashing
- Engine running rough
- Lack of power
- Fuel smell from engine exhaust
- Hesitation or jerking during acceleration
Most Common Causes:
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure
#2: P0420
P0420 indicates an issue with the catalytic converter not functioning properly, which increases the output of harmful pollutants by a vehicle.
Symptoms:
- Check engine light is on
- Lack of power
- Decreased fuel economy
- Rotten egg or sulfur smell
Most Common Causes:
- Faulty oxygen sensor
- Faulty air-fuel sensor
- Worn or internally failing catalytic converter (Most Common)
- A leak in the exhaust system
- Misfire (the root cause of converter failure)
- Rich or Lean air-fuel ratio (the root cause of converter failure)
- Leaded Gasoline (the root cause of converter failure)
#3: P0171
Combustion engines work best by maintaining a fuel to air ratio of about 14.7 parts oxygen to 1 part fuel. If you get a P0171 code, it means that the ratio of fuel to oxygen is off in Bank 1 of your engine and the mixture has too much air (running lean). To try to compensate for this, the powertrain control module injects more fuel into the mixture. But when the ratios become too off-balance, code P0171 is triggered.
Symptoms:
- Check engine light is on
- Lack of power
- Engine âcoughingâ
- Misfire
- Rough idle
Most Common Causes:
- Faulty oxygen sensor
- Dirty or faulty mass airflow sensor
- Vacuum leaks
- Weak fuel pump
- Clogged or dirty fuel injectors
- Clogged fuel filter
- Exhaust leak
- Faulty air-fuel ratio sensor
#4: P0455
P0455 means that the engine control module (ECM) detects a large leak from the evaporative emission control (EVAP) system. This is a problem because it means your vehicle is leaking raw fuel and harmful pollutants into the air, which is bad for the environment and your gas mileage.Â
Symptoms:
- Check engine light is on
- Decreased fuel economy
- Fuel smell
Most Common Causes:
- Missing, defective, damaged, or loose gas cap (most common)
- Cracked EVAP hose
#5: P0301
Like code P0300, this engine code means a misfire has been detected. More specifically, P0301 indicates that Cylinder 1 is experiencing misfires and should be fixed as soon as possible to avoid long-term engine damage.
Symptoms:
- Check engine light is on or flashing
- Engine running rough and/or shaking
- Lack of power
- Fuel smell from the exhaust
- Hesitation or jerking during acceleration
Most Common Causes:
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure
- Faulty fuel injector
#6: P0456
38% of our customers experienced this somewhat tricky to diagnose engine code. Like P0455, this error code indicates that thereâs a leak in the evaporative emission control (EVAP) system. In this case, however, itâs only a small leak (less than .020â in diameter).
Symptoms:
- Check engine light is on
- Decreased fuel economy
- Increased vehicle emissions
- Fuel smell
Most Common Causes:
- Loose or damaged gas cap
- Leaking or disconnected EVAP hose
- Faulty purge volume control valve
- Faulty canister vent control valve
- Charcoal canister leak
- Leaking fuel tank
#7: P0303
Code P0303 indicates a misfire detected in Cylinder 3.
Symptoms:
- Check Engine Light is on
- Check Engine Light flashing
- Engine runs rough and shaking
- Lack of power from the engine
- Fuel smell from the exhaust
- Hesitations/Jerking when accelerating
Most Common Causes:
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure
#8: P0304
Just like the other first couple of 300 codes, P0304 indicates that a misfire has been detected specifically in Cylinder #4 of your engine. Like other cylinder misfires, this should be resolved as quickly as possible to avoid long-term damage to your engine.
Symptoms:
- Check Engine Light is on
- Check Engine Light flashing
- Engine runs rough and shaking
- Lack of power from the engine
- Fuel smell from the exhaust
- Hesitations/Jerking when accelerating
Common Causes:
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure
#9: P0302
P0302 indicates that a misfire has been detected specifically in Cylinder #2 of your engine.
Symptoms:
- Check Engine Light is on
- Check Engine Light flashing
- Engine runs rough and shaking
- Lack of power from the engine
- Fuel smell from the exhaust
- Hesitations/Jerking when accelerating
Most Common Causes:
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure
#10: P0442
Remember the evaporative emission control (EVAP) system that keeps harmful fuel vapors from escaping into the atmosphere? Code P0442 indicates that you have a medium-sized leak (.020â to .040â in diameter) thatâs preventing the EVAP system from doing its job.
Symptoms:
- Check Engine Light is on
- Decreased fuel economy
- Increased vehicle emissions
- Fuel smell
Common Causes:
- Loose or damaged gas cap
- Leaking or disconnected EVAP hose
- Faulty purge volume control valve
- Faulty canister vent control valve
- Charcoal canister leak
- Leaking fuel tank
#11: P0128
P0128 means your engine hasnât reached the correct operating temperature within a specified timeframe. In other words, your engine isnât getting (or staying) hot enough fast enough. While this isnât a severe problem, it can hurt emissions and fuel efficiency so be sure to address it quickly.
Symptoms:
- Check Engine Light is on
- Higher than normal idle
- Decreased fuel economy
- The temperature gauge is unusually low
Most Common Causes:
- Stuck open thermostat (most common)
- Missing Thermostat
- Faulty coolant temperature sensor
- Faulty wiring for coolant temperature circuit
#12: P0174
While not as common as P0171, P0174 means that Bank 2 of your engine has too much air or not enough fuel (running too lean). Driving like this for too long can result in overheating and internal engine damage.
Symptoms:
- Check Engine Light is on
- Lack of power from the engine
- Rough idle
- Engine coughing
- Engine misfiring
Most Common Causes:
- Dirty or faulty mass airflow sensor
- Vacuum leaks â PCV hoses, vacuum hoses, intake manifold gasket
- Weak fuel pump
- Clogged or dirty fuel injectors
- Clogged fuel filter
- Exhaust leak
- Faulty oxygen sensor
- Faulty air-fuel ratio sensor
#13: P0430
P0430 means the catalytic converter in Bank 2 of your engine is not functioning efficiently. Unfortunately, this means itâs not breaking down all those pollutants your engine is producing during the combustion process, which is bad for your lungs, our atmosphere, and fuel economy.
Symptoms:
- Check Engine Light is on
- Lack of power from the engine
- Decreased fuel economy
- Rotten egg or a sulfur smell
Most Common Causes:
- Faulty oxygen sensor
- Faulty air-fuel sensor
- Worn or internally failing catalytic converter (Most Common)
- A leak in the exhaust system
- Misfire (the root cause of converter failure)
- Rich or Lean air-fuel ratio (the root cause of converter failure)
- Leaded Gasoline (the root cause of converter failure)
#14: P0305
P0305 indicates that a misfire has been detected in Cylinder 5 of your engine. This happens when an insufficient amount of fuel is burning in the cylinder and should be addressed immediately to prevent long-term engine damage.
Symptoms:
- Check Engine Light is on
- Check Engine Light flashing
- Engine runs rough and shaking
- Lack of power from the engine
- Fuel smell from the exhaust
- Hesitations/Jerking when accelerating
Most Common Causes:
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure
#15: P0306
P0306 indicates that a misfire has been detected in Cylinder 6 of your engine. This happens when an insufficient amount of fuel is burning in the cylinder and should be addressed immediately to prevent engine damage.
Symptoms:
- Check Engine Light is on
- Check Engine Light flashing
- Engine runs rough and shaking
- Lack of power from the engine
- Fuel smell from the exhaust
- Hesitations/Jerking when accelerating
Most Common Causes:
- Faulty or worn spark plugs
- Faulty spark plug wires or coils
- Distributor failure
#16: P1000
P1000 is a manufacturer-controlled diagnostic trouble code (DTC), used mostly by Ford, Jaguar, and Mazda. Unlike other P-codes, it can mean different things for different vehicles. However, it most likely means that your carâs engine control computer hasnât completed its onboard diagnostic system readiness test. This could be triggered by a loss of power, such as a dead battery or running out of gas.
Symptoms:
- Check engine light is on
Most Common Causes:
- Disconnected battery
- Powertrain Control Module disconnected
- Clearing engine codes
- New vehicle
Detailed Explanation & Diagnosis:Â
Since P1000 is a manufacturer-specific diagnostic trouble code, youâll need an OBD2 scanner to scan your vehicle and find out exactly what it means in your situation.
#17: P0441
Your vehicleâs EVAP system prevents raw fuel from evaporating from the fuel storage system. Ideally, it stores and then purges those vapors back into the combustion process to keep things running smoothly, but when this doesnât happen properly, code P0441 is triggered.
Symptoms:
- Check Engine Light
- Rough Idle
- Erratic Idle
Most Common Causes:
- Faulty purge valve (solenoid)
- Damaged or cracked charcoal canister
- Loose, damaged, or missing gas cap
- Damaged or loose EVAP hosesÂ
#18: P0113
P0113 is defined as Intake Air Temperature (IAT) Sensor Circuit High Input Problem. Simply, Your engineâs computer detects a problem with how much spark and fuel is being injected into the engine which can impact air-fuel ratio, ignition timing, and emissions control. Â
Symptoms:
- Check Engine Light
- Trouble starting the engine
- Engine running lean
Most Common Causes:
- Faulty/Loose IAT sensor
- Faulty/Loose wiring connections
#19: P0446
The EVAP system prevents fuel vapor from escaping and polluting the atmosphere. P0446 is defined as an Evaporative Emission Control System Vent Control Circuit Malfunction. In simple terms, it means thereâs an electrical issue causing the EVAP vent valve to malfunction.
Symptoms:
- Check Engine Light is on
- A slight decrease in fuel economy
- Gasoline smell
Most Common Causes:
- Missing, defective, damaged, or loose gas cap (most common)
- Defective EVAP Canister Vent Control Valve
- Distorted, damaged or cracked Fuel Tank Filler Neck
- Torn or punctured Evaporative system hose(s)
- Defective Fuel Tank Sending Unit gasket or seal
- Split or damaged Carbon Canister
- Defective or damaged fuel tank
- Open or shorted electrical connections
#20: P0102
The 20th most common engine fault code was P0102. When this code is set, it means that your vehicleâs Engine Control Module (ECM) detects a low voltage output from the Mass Air Flow Sensor. In some cases, this code wonât cause any driveability issues, but it can affect fuel mileage.
Symptoms:
- Check Engine Light
- Less power to the engine
- Low fuel consumption â causing engine damage
Most Common Causes:
- Dirty air filter
- Faulty MAF sensor
- Corroded/Damaged MAF circuit terminals
- Carbon covered MAF sensor screens
Check Engine Light? Book Motorly!
After diagnosing various customer’s vehicles, these were the most common car problems experienced. Got a check engine light but not sure what it means? Motorly can help!Â
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