P0102
Mass or Volume Air Flow Sensor A Circuit Low.
- 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
- 02
- FaultThe specific fault in that area
What it means
P0102 means the engine control unit has seen the signal from the mass or volume air flow sensor (circuit A) fall below the expected minimum range. The signal voltage or frequency is lower than the module thinks is possible for the current engine speed and load. This points to a fault in the sensor, its wiring or its supply, or to a metering problem that the module cannot reconcile.
Symptoms
- Malfunction indicator lamp on
- Hard starting or long cranking
- Engine stalls shortly after starting or at idle
- Hesitation, poor acceleration or lack of power
- Rough or unstable idle
- Engine may run in a limp-home mode with fixed fuelling
Possible causes
- Faulty air flow sensor, such as a contaminated or failed sensing elementlikely
- Damaged, chafed or broken wiring in the sensor signal, supply or earth circuitlikely
- Loose, corroded or pushed-out connector terminals at the sensorlikely
- Unplugged sensor connector after recent workpossible
- Air intake restriction, such as a blocked air filter or collapsed intake duct, or a leak or split in the intake after the sensorpossible
- Open circuit or fault in the sensor power supply, relay or fuse (depends on model)possible
- Fault within the engine control unitrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data (engine speed, load, temperature) to see when the fault was set
- Visually inspect the sensor, its connector and the harness for damage, chafing, corrosion, water ingress or a loose fit
- Inspect the air filter, intake ducting and sensor housing for blockages, splits, loose clamps or oil contamination
- With the engine idling, view live air flow data and compare it with the manufacturer's expected value for the engine size; check it rises smoothly when the throttle is opened
- Check the sensor supply voltage, earth and signal wire at the connector with a multimeter, following the wiring diagram for that model
- Wiggle-test the harness and connector while watching live data for dropouts
- Check the relevant fuses and relay for the sensor supply where fitted
- Check for intake air leaks and, if the sensor and wiring test good, compare readings with a known-good sensor before suspecting the control unit
How to fix
- Repair or replace damaged wiring and renew faulty connector terminals
- Refit and secure the sensor connector, cleaning any corrosion
- Replace the air flow sensor if it fails the live data or electrical checks
- Replace a blocked air filter and repair or replace split or collapsed intake ducting
- Repair any intake leaks and replace a failed fuse or relay in the supply circuit
- Repair or replace the control unit only after all other causes have been ruled out and the fault is confirmed
Can I keep driving?
Medium severity
The car can usually be driven short distances, but stalling and poor response can be unsafe in traffic, so get it checked soon. Prolonged driving with incorrect fuelling may cause further problems.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.