MotorBitMost searched codes
P0300
Random/Multiple Cylinder Misfire Detected
The engine is misfiring across more than one cylinder. This is one of the most common reasons a check engine light flash…
P0420
Catalyst System Efficiency Below Threshold (Bank 1)
The catalytic converter on bank 1 is not cleaning exhaust as efficiently as the PCM expects. This is a top search OBD2 c…
P0171
System Too Lean (Bank 1)
Bank 1 is running lean — too much air or not enough fuel. A very common check engine light on many brands.…
P0442
EVAP System Leak Detected (Small Leak)
A small evaporative emissions leak, often a loose gas cap. The light can take days of driving to return after you tighte…
P0128
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
The engine is not reaching normal temperature quickly enough. A stuck-open thermostat is the usual cause.…
P0401
EGR Flow Insufficient Detected
Exhaust gas recirculation flow is lower than commanded. Carbon-clogged EGR passages are extremely common.…
P0135
O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
The upstream oxygen sensor heater on bank 1 failed. The light can come on shortly after startup.…
P0700
Transmission Control System Malfunction
A request from the transmission controller. P0700 is a pointer code — there is usually a more specific TCM code stored.…
P0335
Crankshaft Position Sensor A Circuit Malfunction
Crank sensor circuit fault. This can cause no-start, stalling, or a sudden cut-out.…
The light is on — but you searched a feeling
Most people do not type a P-code. They type what the car is doing. Start here, then confirm with live data.
IDLE
Rough idleShake at a stoplight. Misfire, leak, or idle control — scan before parts.
SHAKE
Shakes when acceleratingLoad misfire vs a tired converter vs a transmission flare.
MPG
Sudden bad mileageRich trims, a stuck-cold thermostat, or a lying MAF.
SMOG
Failed emissionsMIL on, or monitors not ready. Those are different fails.
Set up the iPhone, then read the numbers
SETUP
How to connect an OBD2 adapter to iPhone
Port, ignition, Bluetooth LE / MFi, first scan in MotorBit.
FIX
ELM327 not connecting to iPhone
The usual reasons a dongle pairs on Android and dies on iOS.
PIDS
Live data glossary
MAF, O2 voltage, coolant temp, throttle, engine load.
LIGHT
Why is my check engine light on?
Steady vs flashing, what to do in the first 10 minutes.
Why MotorBit
Built for diagnosis
Codes, live PIDs, charts, monitors, freeze frame, fuel trim — not just a generic code reader screen.
Privacy first
Vehicle data stays on your iPhone. No account required to scan.
ELM327 ready
Works with common Bluetooth OBD2 dongles. Pair, scan, understand the light.