Contaminated or faulty mass air flow sensor giving a false high reading; Short to voltage or signal wire shorted to a power supply in the sensor harness; Damaged, corroded or loose connector terminals at the sensor; Poor or open sensor earth connection causing a raised signal; Air intake leak or airflow disturbance near the sensor, such as a damaged intake pipe or incorrectly fitted air filter housing; Fault in the engine control unit's sensor input or supply circuit.

P0103

Mass or Volume Air Flow Sensor A Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
03: FaultThe specific fault in that area

What it means

P0103 means the engine control unit has seen the signal from the mass or volume air flow sensor (circuit A) sit higher than the expected range, either in voltage or frequency. The reading is higher than the air flow the engine should be drawing at the current load and speed, or it is outside the sensor's plausible range. This often points to a wiring or sensor fault, though the exact threshold varies by engine and manufacturer.

Symptoms

Check engine light on
Rough or unstable idle
Hesitation or poor acceleration
Engine running rich with black smoke or fuel smell
Hard starting or stalling
Higher than normal fuel consumption

Possible causes

Contaminated or faulty mass air flow sensor giving a false high readinglikely
Short to voltage or signal wire shorted to a power supply in the sensor harnesslikely
Damaged, corroded or loose connector terminals at the sensorpossible
Poor or open sensor earth connection causing a raised signalpossible
Air intake leak or airflow disturbance near the sensor, such as a damaged intake pipe or incorrectly fitted air filter housingpossible
Fault in the engine control unit's sensor input or supply circuitrare

How to diagnose

Read all stored codes and freeze frame data, noting engine load, speed and temperature when the code set, and check for other air flow, fuel trim or throttle codes
Inspect the sensor, connector and harness for damage, chafing, water ingress, oil contamination and bent or corroded terminals
Check the air intake path from the filter to the throttle body for splits, loose clamps, a poorly fitted filter or oil-soaked filter element
With the engine idling, view live air flow data and compare it with the manufacturer's expected value for the engine size; it should rise smoothly with revs
Key on, engine off, check the sensor reference supply, earth and signal voltage against the wiring diagram for that model
Test the signal wire for a short to voltage and check the earth for resistance, with the connectors disconnected where the procedure requires
Check fuel trims and compare air flow readings against a known good sensor or the manufacturer's test procedure
Only after the wiring and sensor are ruled out, consider the control unit and check for updates relevant to the fault

How to fix

Clean the sensing element only if the manufacturer permits it, otherwise replace the air flow sensor
Repair or replace the damaged wiring and fix any short to voltage in the harness
Clean, repair or replace the corroded or damaged connector terminals and secure the connector
Restore the sensor earth connection and repair any high resistance in the earth path
Repair intake leaks, replace damaged ducting and refit the air filter and housing correctly
Repair or replace the control unit, or apply a manufacturer calibration update, only where a confirmed fault points to it

Can I keep driving?

Medium severity

The car can usually be driven short distances to a workshop, but the engine may run rich, hesitate or stall, so fix it soon. Avoid long journeys or heavy loads, as a rich mixture can overload the catalytic converter and raise fuel use.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.