TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts
If in TEST 1 the MAP sensor's signal did not increase or decrease as you applied/released to vacuum to the sensor, then there's a good chance that it may not be receiving 5 Volts DC.
To confirm this, we're going to check that the wire labeled with the number 1 in the photo above is supplying 5 Volts DC to the sensor.
If the MAP sensor is receiving power, then our next step is to make sure that it's getting Ground.
Let's get testing:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the red multimeter test lead to the wire labeled with the number 1 using an appropriate tool.
CAUTION: You won't be able to probe the front of the connector's terminal. You'll need to back probe the connector or use a wire piercing probe on the wire. - 3
Connect the black multimeter test lead on the battery's negative post.
- 4
Turn the key to the ON position but don't crank or start the engine.
- 5
Your multimeter should register 4.5 to 5 Volts DC.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 4.5 to 5 Volts. This is the correct result.
The next and last step is to make sure the MAP sensor is getting Ground. Go to: TEST 3: Making Sure The MAP Sensor Is Getting Ground.
CASE 2: The multimeter DID NOT register 4.5 to 5 Volts. Without these 4.5 to 5 Volts DC, the MAP sensor will not function.
Although it's beyond the scope of this article to troubleshoot the cause of these missing voltage, you have now eliminated the MAP sensor as bad.
Resolving the issue that is keeping these 5 Volts from being supplied will solve the MAP sensor issue on your Ford F-Series pickup.
TEST 3: Making Sure The MAP Sensor Is Getting Ground
So far your MAP sensor diagnostic tests have confirmed:
- That the MAP sensor's Hertz frequency signal does not decrease/increase as you apply/release vacuum to it.
- That the MAP sensor is receiving 5 Volts DC.
So in this test that we're going to make sure that the wire labeled with the number 3 is supplying the MAP sensor with Ground.
These are the test steps:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the black multimeter test lead to the wire labeled with the number 3 using an appropriate tool.
CAUTION: You won't be able to probe the front of the connector's terminal. You'll need to back probe the connector or use a wire piercing probe on the wire. - 3
Connect the red multimeter test lead on the battery's positive (+) post.
- 4
Turn the key to the ON position but don't crank or start the engine.
- 5
Your multimeter should register 10 to 12 Volts DC.
OK, let's take a look at what your results mean:
CASE 1: The multimeter registered 10 to 12 Volts. This is the normal and correct result and it lets you know that the MAP sensor is being fed Ground by the PCM.
You can correctly conclude that the MAP sensor bad ONLY if:
- Your MAP sensor did not pass TEST 1.
- Your MAP sensor is getting 5 Volts DC (TEST 2).
- Your MAP sensor is getting Ground (this test section).
CASE 2: The multimeter DID NOT register 10 to 12 Volts. Double check your multimeter connections and repeat the test.
If your multimeter results still do not indicate 10 to 12 Volts, then the MAP is not fried and not the cause of the MAP diagnostic trouble code (DTC) issue.
Here's why: Without a good path to Ground, that the PCM provides internally, the MAP sensor will not work. With this test result, you have eliminated the MAP sensor as bad.
MAP Sensor Code Won't Go Away
So you've tested the MAP sensor and according to your test results, it's good. But the check engine light keeps coming back even after you erased the diagnostic trouble code (DTC) from the computer's (PCM) memory. Well, here are a couple of suggestions that might inspire your next diagnostic move:
- The MAP sensor's vacuum hose or line is torn or cut or clogged.
- The engine has several cylinders with very low engine compression causing it to idle rough and thus producing low or erratic vacuum. I recommend a compression test:
- The MAP sensor is failing intermittently. Which means that it works fine most of the time, but every now and then it doesn't:
- I have found that the best way to test these intermittent problems is to slightly tap the MAP sensor with the handle of a screw-driver and see if this tapping screws up the Hertz signal readings as I apply vacuum.
- The MAP sensor's connector is bad, usually the locking tab is broken and the connector has worked itself loose, causing an intermittent false connection.
- Your fuel pump is starting to go bad and is not sending enough fuel and/or fuel pressure up to the fuel injectors. I suggest a fuel pump test:
- How To Test The Fuel Pump (Ford 4.9L, 5.0L, 5.8L) (at: troubleshootmyvehicle.com).
More Ford F150, F250, F350 Diagnostic Tutorials
You can find more tutorials Ford F150, F250, and F350 in the following index:
Here's a sample of the tutorials you'll find in the index:
- How To Test The Ford Ignition Control Module (Distributor Mounted).
- How To Test The Ford Ignition Control Module.
- Throttle Position Sensor (TPS) Test (Ford 5.0L, 5.8L).
- How To Test The Ford Mass Air Flow (MAF) Sensor.
If this info saved the day, buy me a beer!
