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Browse codes by system

The third character of a P0 code names the subsystem it belongs to. Codes grouped here share a system, which usually means they share causes and diagnostic steps too — a useful thing to know when you have more than one code stored.

Automatic transmission control 1

Transmission Control System Malfunction (MIL Request)

A specific sensor, solenoid or pressure DTC stored in the TCM — 30% of cases

Auxiliary emission controls 1

Exhaust Gas Recirculation Flow Insufficient

Carbon-blocked EGR passages — 45% of cases

Camshaft position and engine synchronization sensing 1

Camshaft Position Sensor A Circuit (Bank 1 or Single Sensor)

Failed camshaft position sensor — 28% of cases

Cooling 1

Coolant Thermostat Below Regulating Temperature

Thermostat stuck open — 64% of cases

Downstream oxygen-sensor heater and catalyst monitoring 1

Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)

Open or failed heater inside Bank 1 Sensor 2 — 33% of cases

Engine speed and position sensing 1

Crankshaft Position Sensor A Circuit Malfunction

Failed crankshaft position sensor — 30% of cases

Evaporative emissions 2

Evaporative Emission System Leak Detected (Small Leak)

Fuel-cap seal hardened, cracked or contaminated — 28% of cases

Evaporative Emission System Leak Detected (Large Leak)

Fuel cap loose, cross-threaded or with a perished seal — 45% of cases

Exhaust / emissions 2

Catalyst System Efficiency Below Threshold (Bank 1)

Catalytic converter genuinely worn out — 40% of cases

Catalyst System Efficiency Below Threshold (Bank 2)

Bank 2 catalytic converter genuinely degraded — 38% of cases

Fuel and air metering 4

Mass or Volume Air Flow "A" Circuit Range/Performance Problem

Contaminated mass-airflow sensing element — 27% of cases

System Too Lean (Bank 1)

Unmetered air leak — vacuum hose, intake boot or gasket — 42% of cases

System Too Rich (Bank 1)

Leaking or over-delivering fuel injector — 27% of cases

System Too Lean (Bank 2)

Intake or vacuum leak affecting bank two — 36% of cases

Idle air and electronic throttle control 1

Idle Control System RPM Higher Than Expected

Vacuum or intake leak bypassing the throttle — 32% of cases

Ignition, fuel and compression 2

Random / Multiple Cylinder Misfire Detected

Worn spark plugs, coils or leads — 38% of cases

Cylinder 1 Misfire Detected

Worn or fouled spark plug on cylinder one — 28% of cases

Intake-air temperature sensing and engine airflow calculation 1

Intake Air Temperature Sensor 1 Circuit High Input

Loose connector, pushed-out pin or spread terminal — 28% of cases

Knock sensing and ignition-timing protection 1

Knock Sensor 1 Circuit (Bank 1 or Single Sensor)

Chafed, open or shorted wiring and loose connector terminals — 29% of cases

Oxygen sensor heater circuit 1

Oxygen Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

Open or failed heater inside Bank 1 Sensor 1 — 34% of cases

Turbocharger or supercharger boost control 2

Turbocharger/Supercharger A Overboost Condition

Sticking wastegate, bypass valve or variable turbo vanes — 28% of cases

Turbocharger/Supercharger A Underboost Condition

Split, loose or swollen charge-air hose or intercooler leak — 30% of cases

Variable valve timing 1

"A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)

Low, dirty or incorrect-viscosity engine oil — 32% of cases