In this tutorial I'll show you an easy way to test the MAF sensor on your Ford Fiesta. The test is done with a multimeter, you don't need a scan tool for this test.
With your test results, you'll find out if the MAF sensor is working or if its bad.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 1.6L Ford Fiesta: 2011, 2012, 2013.
Symptoms Of A Bad MAF Sensor
As you're probably already aware, the mass air flow (MAF) sensor measures the amount of air entering the engine. The fuel injection computer then uses this info to determine the correct amount of fuel to inject into the engine.
If the MAF sensor malfunctions or fails, the fuel injection computer will no longer correctly adjust the air/fuel mixture and engine performance is gonna suffer. You'll see one or more of the following problems:
- Check Engine Light: The check engine light will be shining nice and bright on your dashboard and one of the following diagnostic trouble codes will stored in the computer's memory:
- P0102: MAF Signal Low Input to PCM.
- P0103: MAF Signal High Input to PCM.
- Poor Engine Performance: You may experience a lack of power or hesitation during acceleration, especially under heavy loads or at higher speeds.
- Rough Idling or Stalling: The engine may idle rough or even stall unexpectedly.
- Decreased Fuel Efficiency: A faulty MAF sensor can disrupt the air-fuel mixture, causing the engine to run either too rich (excessive fuel) or too lean (insufficient fuel). The end result is bad gas mileage.
- Black Smoke from Exhaust: An overly rich air-fuel mixture due to a faulty MAF sensor can result in black smoke coming out of the exhaust pipe.
- Difficulty Starting: In some cases, a failing MAF sensor may cause difficulty starting the engine.
- Stalling at Idle: The engine may stall when idling.
- Hesitation or Surging: You might notice hesitation or surging during acceleration or while driving at a consistent speed.
MAF Sensor Circuit Descriptions
In order to correctly diagnose the MAF sensor as good or bad, we need to know what each of the four wires coming out of the connector is doing.
The following table provides a brief description of each wire:
| Terminal | Wire | Description |
|---|---|---|
| 1 | Blue (BLU) | IAT Sensor Signal |
| 2 | White with brown stripe (WHT/BRN) | IAT Sensor Ground (provided by PCM) |
| 3 | Blue with grey stripe (BLU/GRY) | MAF Sensor Signal |
| 4 | White with brown stripe (WHT/BRN) | MAF Sensor Ground (provided by PCM) |
| 5 | -- | Empty |
| 6 | Green with orange stripe (GRN/ORG) | 12 Volts (in RUN or START) |
Where To Buy The MAF Sensor And Save
The following MAF sensors are of known automotive brands (brands that I use myself):
NOTE: Not sure if the indicated MAF sensors fit your particular Ford Fiesta? Don't worry. Once you get to the site, they'll ask you for the specifics of your particular vehicle. If it doesn't fit, they'll find you the right one.
TEST 1: Testing The MAF Signal
To get started, we're gonna check the MAF sensor's output signal and make sure that it reacts to changes in engine speed.
Specifically, the MAF sensor's output voltage signal should increase as engine speed increases and decrease as engine speed decreases.
Generally, when the MAF sensor fails, its output voltage will stay stuck in one value regardless of engine speed.
IMPORTANT: The MAF sensor must be connected to its connector to perform this test. You'll need to use a back probe on the connector or a wire piercing probe on the wire. You can see an example of this tool here: Wire Piercing Probe Review (Power Probe PWPPPPP01).
Let's get started:
- 1
Reconnect the MAF sensor to its electrical connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the black multimeter test lead to the battery (-) negative terminal.
- 4
Connect the red multimeter test lead to the wire labeled with the number 3 using a suitable tool.
- 5
Crank and start the engine and let her idle.
Once the idle stabilizes, take a look at the voltage number or numbers your multimeter is throwing at you. This voltage may fluctuate a little or a lot, and this is OK. Whatever they're doing, this is your base MAF signal voltage. - 6
Accelerate the engine by having a helper step on the gas pedal.
- 7
The voltage value should increase as the engine speed increases.
- 8
Decelerate the engine by having your helper step off the gas pedal.
- 9
The voltage value should decrease as the engine speed decreases.
- 10
Repeat steps 6 through 9 several times to make sure of your test result.
Let's see what your test results mean:
CASE 1: The voltage reading increased/decreased as you increased/decreased the engine speed. This tells you that the MAF sensor is good and is not the cause of the engine performance problem.
CASE 2: The voltage value stayed stuck in one value regardless of engine speed. This usually tells you that the MAF sensor is bad.
To make sure it's bad, we need to check a few more things. For the next test, go to: TEST 2: Making Sure The MAF Sensor Is Getting Power.