OBD-II codes

P2195 Code: O2 Sensor Signal Biased/Stuck Lean (Bank 1, Sensor 1) — Causes, Diagnosis, and Fixes

P2195 means the upstream O2 sensor on bank 1 is stuck reading lean. Fixes range from a $0 reset to a $400 sensor — here's how to tell a bad sensor from a real lean condition.

P0087 Code: Fuel Rail Pressure Too Low

P0087 means fuel rail pressure dropped below spec, usually under load. Common on direct-injection engines. Causes run from a $30 filter to a $2,500 high-pressure pump — here's how to find yours.

P0101 Code: MAF Sensor Range / Performance

P0101 means the MAF reading is implausible — usually a dirty sensor, intake leak, or restriction. Cleaning the wire often fixes it for the price of a $8 can of cleaner.

P0171 Code: System Too Lean (Bank 1) — Causes, Diagnosis, and Fixes

P0171 means the engine is running lean and the PCM is adding extra fuel to compensate. About 40% of cases trace to a vacuum leak, 25% to a dirty MAF sensor. Most fixes land between $0 and $300.

P0174 Code: System Too Lean (Bank 2) — V6 and V8 Diagnostic Patterns

P0174 is the Bank 2 sister to P0171 and only appears on V6 and V8 engines. P0171 and P0174 together usually mean a shared cause (intake plenum, big vacuum leak, weak fuel pump). Either code alone points to a bank-specific cause.

P0300 Code: Random/Multiple Cylinder Misfire — Causes, Diagnosis, and Fixes

P0300 means the PCM detected misfires on multiple cylinders or could not isolate which cylinder. About half of cases trace to ignition (coils, plugs, wires), 20% to fuel delivery. A flashing check engine light alongside P0300 means stop driving.

P0301 Code: Cylinder 1 Misfire — Causes, Diagnosis, and Fixes

P0301 means the PCM detected misfires only on cylinder #1. Causes range from a $4 spark plug to a $300 injector — here's how to isolate the failure cylinder-by-cylinder.

P0335 Code: Crankshaft Position Sensor Circuit Malfunction

P0335 means the PCM lost the crankshaft position signal. The car may not start, may stall randomly, or may run with intermittent misfires. Here's how to confirm sensor vs wiring vs reluctor.

P0420 Code: Catalyst System Efficiency Below Threshold — Causes, Diagnosis, and Fixes

P0420 means the catalytic converter is not cleaning exhaust gases efficiently. Causes range from a $100 O2 sensor to a $2,000 catalyst replacement — here's how to tell which fix you need.

P0430 Code: Catalyst System Efficiency Below Threshold (Bank 2) — V6 and V8 Engines

P0430 is the Bank 2 sister to P0420 and only appears on V6 and V8 engines. The diagnosis is identical except for which side of the engine you investigate. Causes, costs, and the P0420 + P0430 combination explained.

P0442 Code: Small Evaporative Leak Detected — Causes, Diagnosis, and Fixes

P0442 means the evap system has a small leak — usually the fuel cap or a hairline crack in a vapor hose. Here's how to diagnose without a smoke machine.

P0455 Code: Gross Evaporative Leak Detected — Almost Always the Fuel Cap

P0455 means a large evap leak — most commonly a missing or unsealed fuel cap. Here's the 30-second test before you spend money on parts.

P0562 Code: System Voltage Low — Causes and Fixes for the Charging System

P0562 means the PCM measured system voltage below about 10 V. The single most common cause is alternator failure. Often appears alongside the battery warning light. Most fixes land between $130 and $750.