TEST 2: Making Sure The MAF Sensor Is Getting Chassis Ground
The focus of this test section is to verify that the black with white stripe (BLK/WHT) wire of the MAF sensor connector is supplying chassis Ground to the MAF sensor.
The BLK/WHT wire is labeled with the letter B in the photo above.
A voltage test performed with a multimeter will let us if chassis Ground is present in the BLK/WHT wire.
Let's get started:
- 1
Disconnect the MAF sensor from its electrical connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the black multimeter test lead to the BLK/WHT wire of the MAF sensor connector.
The BLK/WHT wire is labeled with the letter B in the photo above.
NOTE: This test is done on the engine wiring harness connector. This connector has round male terminals. - 4
Connect the red multimeter test lead probe the battery positive (+) terminal.
- 5
You should see 10 to 12 Volts on the multimeter.
NOTE: No need to turn the key to the ON position since this is a chassis Ground and is available at all times.
Let's take a look at what your test results mean:
CASE 1: Your multimeter registered 10 to 12 Volts. This test result confirms that chassis Ground is available to the MAF sensor.
The next test is: TEST 3: Making Sure The MAF Sensor Is Getting Ground (PCM).
CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This test result tells you that the BLK/WHT wire is not supplying chassis Ground to the MAF sensor.
The most likely cause of this missing chassis Ground is an open-circuit problem in the BLK/WHT wire.
Although it's beyond the scope of this tutorial, your next step is to find out why this chassis Ground is missing and resolve the issue.
TEST 3: Making Sure The MAF Sensor Is Getting Ground (PCM)
The MAF sensor has a second Ground wire. This second Ground wire is the tan with light blue stripe (TAN/LT BLU) wire.
The difference in this circuit is that it is the fuel injection computer that supplies this Ground.
We'll run a simple voltage test on the TAN/LT BLU wire to verify that it is supplying Ground.
CAUTION: Be careful when testing this circuit! Do not connect this wire to 12 Volts. Otherwise you'll damage the fuel injection computer. The multimeter test suggested below is a safe way to test for the presence of Ground in the wire.
Let's start:
- 1
Disconnect the MAF sensor from its electrical connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the black multimeter test lead to the TAN/LT BLU wire of the MAF sensor connector.
The TAN/LT BLU wire is labeled with the letter C in the photo above.
NOTE: This test is done on the engine wiring harness connector. This connector has round male terminals. - 4
Connect the red multimeter test lead probe the battery positive (+) terminal.
- 5
Turn the key to the ON position but don't crank or start the engine.
- 6
You should see 10 to 12 Volts on the multimeter.
Let's interpret your test result:
CASE 1: Your multimeter registered 10 to 12 Volts. This is the correct result.
Now for our last MAF sensor test: TEST 4: Testing The MAF Signal.
CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This test result tells you that the TAN/LT BLU wire is not supplying Ground from the fuel injection computer to the MAF sensor.
The most likely cause of this missing Ground is:
- An open-circuit problem in the TAN/LT BLU wire between the MAF sensor connector and the fuel injection computer connector.
- A faulty fuel injection computer (very rare).
Although it's beyond the scope of this tutorial, your next step is to find out why this Ground is missing and resolve the issue.
TEST 4: Testing The MAF Signal
So far you have confirmed:
- The MAF sensor is receiving power (TEST 1).
- The MAF sensor is receiving chassis Ground (TEST 2).
- The MAF sensor is receiving Ground from the PCM (TEST 3).
In this last test section, we'll check the performance of the MAF sensor while the engine is running.
This performance test will check the MAF sensor signal voltage and see if it varies with engine speed.
Specifically, you should see:
- The MAF signal voltage increase when engine speed increases.
- The MAF signal voltage decrease when engine speed decreases.
Generally, when the MAF sensor fails, its voltage signal stays stuck in one value regardless of engine speed.
NOTE: It's important that the engine is at normal operating temperature. So start the engine and let it reach normal operating temperature.
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).
These are the test steps:
- 1
Reconnect the MAF sensor to its electrical connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the red multimeter test lead to the LT BLU/RED wire using a suitable tool.
The LT BLU/RED wire is labeled with the letter D in the photo above. - 4
Connect the black multimeter test lead to the battery (-) negative terminal.
- 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
Open the throttle (manually) to increase engine speed.
- 7
The voltage value should increase as the engine speed increases.
- 8
Release the throttle to decrease engine speed.
- 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 examine your test result:
CASE 1: The signal voltage reading increased/decreased as you increased/decreased the engine speed. This test result indicates that the MAF sensor is good.
CASE 2: The signal voltage value stayed stuck in one number as you increased/decreased the engine speed. With this test result, you can conclude that the mass air flow (MAF) sensor is bad if you have:
- Confirmed the MAF sensor is receiving power (TEST 1).
- Confirmed the MAF sensor is receiving chassis Ground (TEST 2).
- Confirmed the MAF sensor is receiving Ground from the PCM (TEST 3).
- Confirmed the MAF voltage signal does not increase/decrease as engine speed increases/decreases (this test section).
More 3.0L Ford Ranger Tutorials
You can find a complete list of tutorials here:
Here's a sample of the tutorials you'll find there:
- How To Test The Engine Compression (1991-2008 3.0L Ford Ranger).
- How To Test The Blower Motor (1998-2000 3.0L Ford Ranger).
- How To Test The Front O2 Sensor Heater (1998-2001 3.0L Ford Ranger).
- Rear O2 Sensor Heater Test (1998-2001 3.0L Ford Ranger).
If this info saved the day, buy me a beer!
