How To Test The MAP Sensor (1991 5.2L, 5.9L V8 Dodge Ram Van)

TEST 3: Verifying The MAP Sensor Ground Circuit

Alright, based on the last two tests, here's what we know:

• First off, the MAP sensor isn't putting out a changing voltage when vacuum is applied or released (TEST 1).
• Second, it's getting power —you saw 4.5 to 5 Volts DC on your meter (TEST 2).

Now for the last check —we're gonna make sure the MAP sensor's getting a solid Ground. You'll use a multimeter again for this step.

This one's pretty simple. You'll test the black with light blue stripe (BLK/LT BLU) wire of the MAP sensor's connector. That's the wire that feeds Ground to the sensor.

IMPORTANT: That Ground wire connects straight to the fuel injection computer, so be careful not to connect it to battery voltage (12V) or you'll fry the computer. Follow the steps below for a safe and easy way to check Ground.

Here's how to run the test:

1. 1

   Unplug the MAP sensor from its connector.

2. 2

   Attach the red lead from your multimeter to the battery's positive (+) terminal.

3. 3

   Set your multimeter to Volts DC.

4. 4

   Turn the key to ON, but don't start the engine.

5. 5

   Use the black multimeter lead to probe the terminal marked number 1.
   
   NOTE: Check it's the one that connects to the BLK/LT BLU wire.

6. 6

   Your meter should read somewhere between 10 and 12 Volts DC.

Here's how to read your results:

CASE 1: You got 10 to 12 Volts. That means the sensor's getting proper Ground from the computer.

If you've confirmed all of this:

• The MAP sensor doesn't respond to vacuum with a changing voltage (TEST 1).
• It's receiving 4.5 to 5 Volts of power (TEST 2).
• And now, it's confirmed to have a working Ground.

Then yeah, it's time to replace the sensor —it's shot.

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CASE 2: You didn't get 10 to 12 Volts. Go back and double-check your test connections, then try again.

If it's still not showing 10 to 12 Volts, now you know why the MAP sensor can't send out a variable signal —it's missing Ground.

So the sensor isn't the issue. Your next move is to restore that Ground connection. The most common causes include:

• A break or fault in the Ground wire running between the MAP sensor and the fuel injection computer.
• Less common, but still possible —an internal failure inside the computer.

MAP Sensor Code Won't Go Away

So you've already tested the MAP sensor and everything checks out —it's working like it should. But that check engine light just won't quit, even after you've cleared the code (DTC) from the system?

Let's go a bit further and look at a few things that might be slipping under the radar:

1. Big vacuum leak: A major vacuum leak can mess with the air/fuel mixture —making it too lean. That can cause rough idle and trick the computer into blaming the MAP sensor.
2. Cracked or leaking vacuum hose: Take a good look at the rubber hose running to the MAP sensor. If it's cracked, damaged, or falling apart, it could be throwing off the readings.
3. Low compression in the engine: If multiple cylinders are running low on compression, it'll mess with vacuum and cause the engine to idle rough. Do a compression test to be sure:
   • How To Test Engine Compression (1989-2003 5.2L, 5.9L V8 Dodge Ram Van).
4. MAP sensor failing off and on: Sometimes a sensor works fine... until it doesn't. It might be acting flaky. Try lightly tapping it with a screwdriver handle while applying vacuum. If the voltage spikes or drops suddenly, you've found the issue.
5. Loose or broken MAP sensor connector: Check the connector at the sensor itself. If the locking tab is broken or damaged in any way, the signal could be cutting in and out (false connection issue).
6. Weak fuel pump: If your fuel pump isn't delivering the right pressure, the engine won't run right —and that can lead to false MAP sensor codes too. Check your fuel pressure and make sure it's where it should be.

More 5.2L, 5.9L V8 Dodge Ram Van Tutorials

I've written several more tutorials for the 5.2L, 5.9L V8 Dodge Ram vans and you can find them in this index:

• 5.2L, 5.9L V8 Dodge Ram Van Index Of Tutorials.

Here's a sample of the tutorials you'll find in the index:

• How To Test The Intake Air Temp (IAT) Sensor (1992-1997 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test The TPS (1991 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test Engine Compression (1989-2003 5.2L, 5.9L V8 Dodge Ram Van).
• How To Test For A Blown Head Gasket (1989-2003 5.2L, 5.9L V8 Dodge Ram Van).