P0102 Code: Mass Air Flow Sensor A Circuit Low Input
The MAF signal is too weak for the PCM to accept, so it treats the circuit as dead and estimates airflow.
At a glance
Severity: Moderate
- Meaning
- Mass Air Flow Sensor A Circuit Low Input
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $0–$1,200
- DIY difficulty
- Easy
A running engine always moves air, so the PCM expects the mass air flow sensor to report anything from a few grams per second at idle to well over 100 g/s at full throttle. P0102 sets when the signal falls below the lowest value a working sensor can produce with the crankshaft turning, typically under about 0.2 V on an analog sensor or a frequency far below the idle range on a digital one. To the PCM that means no air at all, which is physically impossible, so it stops trusting the sensor and calculates load from throttle angle and rpm instead. The usual culprits are refreshingly simple: a plug left off or only half-latched after an air filter job, no power reaching the sensor, an open signal wire, or a hot-film element that has burned out.
Can I keep driving? You can usually drive gently to a shop, but the fallback fuel map is crude: expect a stumble off the line, stalling at stops and, on turbo diesels, a hard power cut. Put off long trips and towing until the circuit is repaired.
How to read P0102
- P Powertrain
- 0 Generic (SAE)
- 1 Fuel & air metering
- 02 Specific fault
Symptoms
- Check engine light comes on within seconds of start-up
- Engine starts, then dies after a few seconds on some models
- Flat, sluggish acceleration, worst from a standstill
- Lean stumble or popping from the intake when you open the throttle quickly
- Scanner shows 0.0 g/s or a fraction of a gram per second at idle
- Turbo diesels drop into limp mode with almost no boost
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- MAF connector unplugged, unlatched or pulled loose by the air-box lid after a filter change
- No supply voltage: blown engine-sensor fuse or failed main relay feeding the sensor
- Open or high-resistance signal wire between the sensor and the PCM
- Burned-out or cracked hot-film element (dead sensor)
- Signal wire rubbed through and shorted to ground
- PCM input circuit fault
Diagnosis step by step
Read MAF airflow before touching anything
At warm idle a healthy sensor reports roughly 2 to 4 g/s on a 2.0-liter four-cylinder and about 5 to 7 g/s on a 5.3-liter V8. If the value sits at or near zero and doesn't climb when you hold 2,500 rpm, the PCM really isn't getting a signal. Note any oxygen-sensor heater codes too, since they can share the MAF's fuse.
Tools: OBD-II scanner
Check the plug and the air box
Confirm the connector is pushed fully home with its locking tab engaged, and that the air-box lid or intake duct isn't stretching the harness. Unplug it once and look for terminals that are pushed back, bent or crusted green.
Tools: Flashlight
Measure power and ground at the connector
Key on, engine off, back-probe the sensor. The power pin should show battery voltage, about 12.4 V, or 5 V on some designs, and the ground pin should be within 0.1 V of battery negative. No voltage on the power pin sends you to the fuse and relay before anything else.
Tools: Multimeter
Read the signal pin directly
An analog sensor usually shows about 0.5 to 1.0 V key-on engine-off, a bit more at idle and over 3.5 V on a hard rev. A signal stuck between 0 and 0.2 V with good power and ground means the sensor isn't producing an output. Frequency-type sensors, common on GM V8 trucks, need the meter's Hz setting and typically run about 2 to 3 kHz at idle.
Tools: Multimeter
Test the signal wire end to end
Disconnect the battery, unplug the sensor and the PCM connector, and measure the signal wire from pin to pin: it should be well under 1 ohm. Then check that wire to engine ground; any reading other than open means the insulation has worn through somewhere.
Tools: Multimeter
Verify the repair under load
Clear the code and watch airflow rise smoothly with rpm. As a sanity check, 2,500 rpm with no load should read roughly two and a half to three times the idle figure, with no dropouts when you blip the throttle.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Reconnect and latch the MAF connector | Yes | $0 |
| Replace blown sensor fuse or main relay | Yes | $5–$80 |
| Repair open or grounded signal wire | No | $120–$350 |
| Replace MAF sensor (OE-quality) | Yes | $150–$450 |
| PCM diagnosis and repair or replacement | No | $400–$1,200 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Chevrolet
Chevrolet trucks and SUVs with the 4.8, 5.3 and 6.0 V8s use a frequency-output MAF sensor, so a plain DC voltage reading on the signal wire tells you little. Use a meter with a Hz setting or the scan tool; a steady reading in the low kilohertz range at warm idle is normal.
Field data
| Nissan | 5 | Kicks, Rogue, Rogue Sport | |
|---|---|---|---|
| Ford | 2 | Edge, F-150 REGULAR CAB | |
| GMC | 2 | Sierra 3500, Yukon Xl |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
Any state that plugs into the OBD-II port during a smog or emissions test fails the car while the check engine light is on for P0102. After the repair, allow a few days of mixed driving so the readiness monitors complete before you retest.
Frequently asked questions
Why does P0102 so often show up right after an air filter change?
The MAF usually sits on the air-box outlet, and its plug is easy to stretch, knock loose or forget when the lid comes off. If the code appeared on the first start after the service, check that connector before you buy anything.
Will cleaning the MAF sensor fix P0102?
Rarely. Cleaning helps when dirt makes the airflow reading drift, which is a P0101 problem. P0102 means the signal has almost vanished, and that is electrical: no power, an open wire or a dead element.
Why does my car stall right after starting with P0102?
On some engines the substitute fueling at start-up is too lean to hold a stable idle, especially when cold. Once warm, the engine often keeps running. Restoring the MAF signal cures the stalling.
Can I just drive with the MAF unplugged?
For a short distance, yes, since the PCM falls back to estimated airflow. The engine runs less smoothly, uses more gas and keeps the light on, so treat it as a way to limp home, not as a repair.