P0300 Random/Multiple-Cylinder Misfire: Meaning and Tests
The controller detected crankshaft-speed variation consistent with combustion loss across more than one cylinder.
Category Trouble Codes
Code definitions explained as monitoring results rather than automatic parts verdicts.
P0171 System Too Lean Bank 1: A Fuel-Trim Workflow
The controller reached a calibrated positive fuel correction because feedback indicated a lean condition on bank 1.
P0420 Catalyst Efficiency Below Threshold: What to Prove First
The catalyst monitor judged oxygen-storage performance below its calibrated threshold; the code does not prove the converter is the first failed part.
P0455 EVAP Large Leak Detected: A Sealed-System Test Path
The evaporative monitor could not create or hold the expected vacuum or pressure, or it detected flow consistent with a large leak.
P0128 Coolant Temperature Below Thermostat Regulating Range
Warm-up behavior did not match the calibrated time and load model, commonly because measured coolant temperature rises too slowly.
P0562 System Voltage Low: Battery, Charging, or Connection?
A control module measured supply voltage below its calibrated threshold for the required time.
P0135 Oxygen Sensor Heater Circuit: Test the Circuit
The controller detected an electrical or performance fault in the bank 1 sensor 1 heater circuit.
P0442 EVAP Small Leak Detected: Finding a Small Leak
The EVAP monitor detected leakage smaller than a large-leak threshold, which makes test setup and stable sealing especially important.
U0100 Lost Communication With ECM/PCM: Network Triage
Another module reported that expected communication with the engine or powertrain controller was absent.
C0035 Left-Front Wheel-Speed Circuit: Signal Before Sensor
A chassis controller detected a left-front wheel-speed circuit or signal fault; code wording varies by manufacturer.