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OBD2 check engine codes for Mercury

Mercury was discontinued by Ford in 2011; vehicles like the Milan, Mariner, and Mountaineer share their platforms and powertrains entirely with Ford Fusion, Escape, and Explorer. OBD2 diagnosis for Mercury models is identical to their Ford equivalents—same code patterns, same repair procedures, same parts. The 4.6L V8 in the Grand Marquis is essentially a Crown Victoria powertrain with well-documented OBD2 failure points.

Select a code below for Mercury-specific causes, affected models, and repair cost estimates.

P0420Catalyst System Efficiency Below Threshold (Bank 1)P0171System Too Lean (Bank 1)P0174System Too Lean (Bank 2)P0300Random/Multiple Cylinder Misfire DetectedP0442Evaporative Emission System Leak Detected (Small Leak)P0455Evaporative Emission System Leak Detected (Large Leak)P0128Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature)P0430Catalyst System Efficiency Below Threshold (Bank 2)P0401Exhaust Gas Recirculation Flow InsufficientP0507Idle Air Control System RPM Higher Than ExpectedP0340Camshaft Position Sensor Circuit MalfunctionP0440Evaporative Emission System Control System MalfunctionP0172System Too Rich (Bank 1)P0101Mass Air Flow Circuit Range/PerformanceP0113Intake Air Temperature Sensor Circuit HighP0135O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)P0141O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)P0700Transmission Control System MalfunctionP0715Input/Turbine Speed Sensor Circuit MalfunctionP2195O2 Sensor Signal Stuck Lean (Bank 1, Sensor 1)P2181Cooling System PerformanceP0301Cylinder 1 Misfire DetectedP0302Cylinder 2 Misfire DetectedP0456Evaporative Emission System Leak Detected (Very Small Leak)P0500Vehicle Speed Sensor (VSS) MalfunctionP0520Engine Oil Pressure Sensor/Switch Circuit MalfunctionP0446Evaporative Emission System Vent Control CircuitP0410Secondary Air Injection System MalfunctionP0730Incorrect Gear RatioP0102Mass Air Flow Circuit Low InputP0117Engine Coolant Temperature Circuit Low InputP0341Camshaft Position Sensor Range/PerformanceP0011Camshaft Position A – Timing Over-Advanced or System Performance (Bank 1)P0012Camshaft Position A – Timing Over-Retarded (Bank 1)P0014Camshaft Position B – Timing Over-Advanced or System Performance (Bank 1)P0021Camshaft Position A – Timing Over-Advanced or System Performance (Bank 2)P0016Crankshaft/Camshaft Position Correlation – Bank 1, Sensor AP0017Crankshaft/Camshaft Position Correlation – Bank 1, Sensor BP0087Fuel Rail/System Pressure – Too LowP0303Cylinder 3 Misfire DetectedP0304Cylinder 4 Misfire DetectedP0305Cylinder 5 Misfire DetectedP0306Cylinder 6 Misfire DetectedP0325Knock Sensor 1 Circuit Malfunction (Bank 1)P0335Crankshaft Position Sensor A Circuit MalfunctionP0351Ignition Coil A Primary/Secondary Circuit MalfunctionP0352Ignition Coil B Primary/Secondary Circuit MalfunctionP0353Ignition Coil C Primary/Secondary Circuit MalfunctionP0354Ignition Coil D Primary/Secondary Circuit MalfunctionP0131O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)P0133O2 Sensor Slow Response (Bank 1, Sensor 1)P0122Throttle/Pedal Position Sensor A Circuit Low InputP0505Idle Air Control System MalfunctionP0201Injector Circuit / Open — Cylinder 1P0741Torque Converter Clutch Circuit Performance or Stuck OffP0118Engine Coolant Temperature Circuit High InputP0562System Voltage LowP0606ECM/PCM Processor Fault

Frequently asked questions

What are the most common check engine codes for Mercury?

The most frequently seen OBD2 codes on Mercury vehicles include P0420 (catalyst efficiency), P0171 (system lean), P0300 (random misfire), P0128 (coolant below thermostat temperature), and P0442 (EVAP small leak). Select any code above for Mercury-specific causes and repair guidance.

Can I diagnose Mercury OBD2 codes myself?

Yes. A basic Bluetooth OBD2 scanner ($20–$40) paired with a free app will read all standard P-codes on any Mercury. For manufacturer-specific codes or advanced system faults, a professional scan tool provides more detail. Most auto parts stores will also read codes for free.

How much does it cost to fix a check engine code on a Mercury?

Repair costs vary widely by code and model. Simple fixes like a loose gas cap or a sensor replacement run $20–$150. Moderate repairs such as an oxygen sensor, thermostat, or ignition coil typically cost $150–$400. Major repairs like a catalytic converter or transmission component can run $500–$2,500 or more. Each code page includes a specific cost range.

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

It depends on the code. Many codes—like EVAP leaks or minor sensor faults—are safe to drive with for a few days. A flashing check engine light or codes related to misfires, oil pressure, or overheating require stopping immediately. Look up your specific code for a direct answer.

Browse Mercury by model year

Year-specific guides include Mercury-tailored causes and repair costs.

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