Can I keep driving with the check engine light on?

It depends on how the light behaves. A steady light usually means you can drive to a shop, though the fault is real and can get worse. A flashing light means an active misfire is dumping unburned fuel into the catalytic converter, which can ruin the converter in minutes. Pull over safely and stop driving when the light flashes.

Does the code tell me which part to replace?

No. The code identifies the circuit or system that fell outside its expected range, not the component that failed. The part that reports a problem is often working correctly and reporting it accurately. Work through the diagnostic steps on the code page before buying anything.

Will clearing the code fix the problem?

Clearing erases the record, not the fault. It also resets the readiness monitors, and most emissions programs will fail a vehicle until those monitors complete a full drive cycle. If the underlying fault is still present, the light comes back.

Do I need my own scan tool?

Not to get started. Many chain auto parts stores in the US read stored codes for free. Owning a basic reader pays for itself quickly if you keep an older vehicle running, mostly because it lets you watch live data rather than just the stored code.

What is the difference between a P0 and a P1 code?

P0 codes are generic and mean the same thing on every manufacturer. P1 codes are manufacturer-specific, so a P1450 on a Ford is unrelated to a P1450 on another brand. Where a code is make-specific, the code page says so and names the make.

OBD-II Diagnostic Trouble Codes

Type a code to filter the list. Every page explains the code in plain language: what it means, the most likely causes, and how to diagnose it without throwing parts at the problem.

How to read a trouble code

Every OBD-II code has the same four-part shape. The letter names the system: P for powertrain, B for body, C for chassis, U for network. The first digit says whether the code is generic across all manufacturers (0) or specific to your make (1). The next digit points at the subsystem, such as fuel and air metering, ignition, or emissions. The last two digits identify the exact fault.

A code names the circuit the computer saw out of range. It does not name the broken part. P0171 means bank 1 is running lean, and the ECU worked that out from fuel-trim math. The actual cause could be a vacuum leak, a tired fuel pump, a contaminated MAF sensor, or an exhaust leak ahead of the upstream oxygen sensor. Replacing the sensor that reported the problem is the most common and most expensive mistake in home diagnostics.

Every code page here follows the same order: what the code means, the symptoms you are likely to notice, the causes ranked by how often they turn out to be the culprit, and the diagnostic steps in the sequence a technician would actually run them. Nothing is behind a signup or a paywall.

Common questions about trouble codes

Can I keep driving with the check engine light on?: It depends on how the light behaves. A steady light usually means you can drive to a shop, though the fault is real and can get worse. A flashing light means an active misfire is dumping unburned fuel into the catalytic converter, which can ruin the converter in minutes. Pull over safely and stop driving when the light flashes.
Does the code tell me which part to replace?: No. The code identifies the circuit or system that fell outside its expected range, not the component that failed. The part that reports a problem is often working correctly and reporting it accurately. Work through the diagnostic steps on the code page before buying anything.
Will clearing the code fix the problem?: Clearing erases the record, not the fault. It also resets the readiness monitors, and most emissions programs will fail a vehicle until those monitors complete a full drive cycle. If the underlying fault is still present, the light comes back.
Do I need my own scan tool?: Not to get started. Many chain auto parts stores in the US read stored codes for free. Owning a basic reader pays for itself quickly if you keep an older vehicle running, mostly because it lets you watch live data rather than just the stored code.
What is the difference between a P0 and a P1 code?: P0 codes are generic and mean the same thing on every manufacturer. P1 codes are manufacturer-specific, so a P1450 on a Ford is unrelated to a P1450 on another brand. Where a code is make-specific, the code page says so and names the make.

OBD-II Diagnostic Trouble Codes

How to read a trouble code

Common questions about trouble codes

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