Check engine light codes: what they mean and how urgent

A check engine code such as P0300, P0171 or P0420 names the system that reported a problem, not the part that failed. Search your code below to see what it means, the usual causes a technician tests, and how soon to act. A flashing light, overheating or low oil pressure means stop and call. From the technicians at Prestige Auto Repairs & Tires in Oakland Park and Fort Lauderdale.

Search codes

P0300Stop and check soon
Random or multiple cylinder misfire
Usual causes to test: Worn spark plugs, failing ignition coils, a vacuum leak, low fuel pressure or a leaking injector.
P0301–P0308Stop and check soon
Misfire in one cylinder (the last digit is the cylinder)
Usual causes to test: Usually that cylinder’s spark plug, ignition coil or injector; sometimes low compression.
P0171Book a diagnosis
System too lean, bank 1
Usual causes to test: Vacuum or intake leak, dirty mass airflow sensor, weak fuel pump or clogged fuel filter.
P0174Book a diagnosis
System too lean, bank 2
Usual causes to test: Same causes as P0171; when both banks are lean, look for a shared leak or fuel delivery problem.
P0172Book a diagnosis
System too rich, bank 1
Usual causes to test: Leaking injector, high fuel pressure, a faulty airflow or coolant temperature sensor.
P0420Book a diagnosis
Catalytic converter efficiency below threshold, bank 1
Usual causes to test: An exhaust leak, a failing oxygen sensor, an earlier misfire, or a worn converter.
P0430Book a diagnosis
Catalytic converter efficiency below threshold, bank 2
Usual causes to test: Same causes as P0420 on the other side of a V engine.
P0440–P0457Can wait a little
Evaporative (EVAP) system leak or fault
Usual causes to test: A loose or worn gas cap, a cracked hose, a stuck purge or vent valve. Found with a smoke test.
P0128Can wait a little
Engine slow to reach operating temperature
Usual causes to test: A thermostat stuck open, or a faulty coolant temperature sensor.
P0217Stop and check soon
Engine over temperature
Usual causes to test: Low coolant, a failed water pump or fan, a blocked radiator. Pull over and turn the engine off.
P0101Book a diagnosis
Mass airflow sensor range or performance
Usual causes to test: A dirty or failing airflow sensor, an air leak after the sensor, a blocked air filter.
P0130–P0167Book a diagnosis
Oxygen sensor circuit or performance
Usual causes to test: A failed oxygen sensor or heater, damaged wiring, or an exhaust leak near the sensor.
P0335Stop and check soon
Crankshaft position sensor circuit
Usual causes to test: A failed sensor or wiring. The engine may stall or refuse to start.
P0340Book a diagnosis
Camshaft position sensor circuit
Usual causes to test: A failed sensor, wiring, or on some engines a timing or camshaft adjuster problem.
P0011 / P0014Book a diagnosis
Camshaft timing over-advanced or retarded, bank 1
Usual causes to test: Low or dirty oil, a sticking oil control solenoid or camshaft adjuster, a stretched timing chain.
P0016Stop and check soon
Crankshaft and camshaft position do not agree
Usual causes to test: A stretched timing chain or worn guides, a slipped belt, or a faulty sensor. Common on some European engines.
P0401Can wait a little
EGR flow insufficient
Usual causes to test: Carbon in the EGR valve or passages, a stuck valve, or a vacuum or electrical fault.
P0455Can wait a little
EVAP large leak detected
Usual causes to test: Most often a missing or loose gas cap; otherwise a disconnected or cracked hose.
P0700Book a diagnosis
Transmission control system fault
Usual causes to test: The transmission computer has its own code stored. It needs a scan of the transmission module to find it.
P0562Book a diagnosis
System voltage low
Usual causes to test: A weak battery, a failing alternator, or a poor ground or battery connection.
P0520Stop and check soon
Oil pressure sensor or switch circuit
Usual causes to test: Often the sensor or its wiring, but check the oil level and pressure first: low oil pressure destroys engines.
P0299Book a diagnosis
Turbocharger underboost
Usual causes to test: A boost leak in a hose or intercooler, a sticking wastegate or diverter valve, or a worn turbocharger.

Book a diagnosis (954) 303-0758

After the code

A code is where the diagnosis starts

We save the freeze-frame data before anything is cleared, read every module, check the maker’s technical bulletins, then test the likely causes with live data and a smoke test for leaks. You get photos and a written estimate that names the cause. Read more in our guide to what a code scan can and can’t tell you, or see check engine light diagnostics in Fort Lauderdale and in Oakland Park.

Other lights on too? Start with the dashboard warning lights guide.

What does a check engine code tell me?

It tells you which system reported a problem and what the engine computer saw, not which part failed. P0171, for example, means the engine is running lean, which can come from a vacuum leak, a dirty airflow sensor or a weak fuel pump. A diagnosis tests each possibility before anything is replaced.

What do the letters and numbers in a code mean?

The first letter is the system: P for powertrain (engine and transmission), B for body, C for chassis and U for network. A 0 after the letter means a generic code used by every maker; a 1 means a maker-specific code. The last digits point to the circuit or fault.

Is it safe to drive with the check engine light on?

If the light is steady and the car drives normally, it is usually safe to drive to a shop soon. If it is flashing, the engine is misfiring badly enough to damage the catalytic converter: ease off and have it checked right away. Stop if the light comes with overheating or low oil pressure.

Can you read the codes at both shops?

Yes. Both shops read every module, not only the engine, with factory-level software for European cars, and test the likely causes before recommending a repair. Oakland Park, 250 NE 44th St, is open 7 days; Fort Lauderdale, 930 NE 4th Ave, Monday to Saturday; both 8 AM to 7 PM.