Cars & OBD · P0299
P0299 Code: Underboost Does Not Always Mean a Failed Turbo
P0299 reports underboost. Check the engine-specific diagnostic path before assuming the turbocharger needs replacing.
Car & OBD-II trouble codes
Find the meaning of a diagnostic trouble code, possible causes and what to discuss with your workshop.
Available guides
Cars & OBD · P0442
P0442 Code: Small EVAP Leak, Checks and Repair Verification
P0442 reports a small EVAP leak. Preserve the scan results and confirm the vehicle-specific test finding before replacing caps, valves or a canister.
Cars & OBD · P0301
P0301 Code: Cylinder 1 Misfire and the Next Diagnostic Steps
P0301 identifies a cylinder 1 misfire. Confirm the engine’s cylinder layout and diagnostic evidence before replacing a coil, plug or injector.
Cars & OBD · P0456
P0456 Code: A Small EVAP Leak Needs a Confirmed Diagnosis
P0456 reports a very small EVAP leak. The code does not locate the problem; vehicle-specific testing should confirm the cause before parts are replaced.
Cars & OBD · P0128
P0128 Code: Coolant Temperature and Thermostat Checks
P0128 means coolant stayed below the expected regulating temperature. Check the vehicle-specific diagnosis before replacing a thermostat.
Cars & OBD · P0174
P0174 Code: System Too Lean on Bank 2 and What to Check Next
P0174 reports a lean condition on Bank 2. The useful next step is to preserve the diagnostic data and find out why fuel control has reached its limit, rather than choosing a sensor from the code alone.
Cars & OBD · P0171
P0171 Code: System Too Lean (Bank 1), Causes and Next Steps
P0171 means the engine control system has detected a lean condition on Bank 1. An air leak can be responsible, but the code does not identify a failed oxygen sensor or a specific replacement part.
Cars & OBD · P0420
P0420 Code: Catalyst Efficiency, Possible Causes and Diagnosis
P0420 means the catalyst system on Bank 1 is performing below its accepted efficiency threshold. The result needs diagnosis: it is not, by itself, an instruction to replace an oxygen sensor or catalytic converter.
Cars & OBD · P0300
P0300 Code: Random Misfire, Warning Lights and Diagnosis
P0300 reports a random misfire. Ford’s diagnostic reference describes multiple cylinders misfiring or a misfire that the control module cannot assign to one cylinder.