How To Test The MAP Sensor (1992-1997 5.2L, 5.9L V8 Dodge Ram Van)

TEST 3: Verifying The MAP Sensor Ground Circuit

Alright, let's go over what we've got so far based on the last two tests:

• First, the MAP sensor isn't putting out a changing voltage when you apply or release vacuum (TEST 1).
• Second, it is getting power —a solid 4.5 to 5 Volts DC (TEST 2).

Now we're down to the final step —let's make sure the sensor's got a reliable Ground connection. You'll need your multimeter for this one too.

You're gonna test the black with light blue stripe (BLK/LT BLU) wire at the MAP sensor's 3-wire connector. That's the wire that feeds Ground to the sensor.

IMPORTANT: That Ground wire connects directly to the fuel injection computer. Never connect it directly to battery power —doing that will fry the computer. The steps below outline a safe method to check if Ground is present in the circuit.

Here's how to test for Ground:

1. 1

   Unplug the MAP sensor from its connector.

2. 2

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

3. 3

   Set the meter to DC Volts.

4. 4

   Turn the ignition to ON —don't start the engine.

5. 5

   Use the black meter lead to probe terminal 1 on the connector.
   
   Confirm that this terminal corresponds to the BLK/LT BLU wire —the sensor's Ground wire.

6. 6

   If Ground is present, you'll get a reading between 10 and 12 Volts DC.

Let's break down what your reading means:

CASE 1: Your meter shows 10 to 12 Volts. That confirms the MAP sensor's Ground circuit is working right —the computer's providing a good Ground signal.

So, if:

• You saw no variable voltage during the vacuum test (TEST 1),
• You confirmed 4.5 to 5 Volts of power in (TEST 2), and
• You now know the sensor's got Ground,

Then the MAP sensor's bad —go ahead and replace it.

Check out my replacement recommendations here: Where to Buy the MAP Sensor and Save.

CASE 2: You didn't see 10 to 12 Volts. Double-check your connections. Try the test again to rule out a simple setup issue.

If you still don't see the indicated voltage, you've found the cause of the MAP sensor problem —it isn't getting Ground.

That usually means the sensor itself is fine. Instead, you'll need to trace and fix the missing Ground. The most likely causes are:

• A broken or damaged Ground wire between the sensor and the computer.
• Less common, but possible —an internal failure in the fuel injection computer.

MAP Sensor Code Won't Go Away

So, you've already run all the MAP sensor tests and everything checks out. But that check engine light keeps coming back —even after you cleared the DTC from the system?

Time to look a little closer. Something else could be throwing that code. Here are some common issues that can act just like a bad MAP sensor:

1. Big vacuum leak: A serious vacuum leak can mess with the air/fuel mix, cause rough idling, and fool the computer into thinking the MAP sensor's bad.
2. Cracked or busted vacuum elbow: Take a good look at the rubber elbow that connects the MAP sensor's vacuum inlet to the throttle body. If it's broken, cracked, or falling apart, that alone can trigger a bad MAP readings leading to a MAP trouble code.
3. Low engine compression: Weak compression across multiple cylinders can mess with vacuum levels and cause a rough idle. It's a good idea to run a compression test and rule this out:
   • How To Test Engine Compression (1989-2003 5.2L, 5.9L V8 Dodge Ram Van).
4. Intermittent MAP sensor failure: Sometimes a sensor works one minute, fails the next. Try gently tapping it with a screwdriver handle while applying vacuum. If the signal voltage glitches out, you've found the source of the problem.
5. Loose or damaged sensor connector: Look closely at the MAP sensor connector. A loose fit or broken locking tab can cause an intermittent connection, loss of the MAP signal and a MAP sensor DTC.
6. Failing fuel pump: A weak pump will not deliver the fuel your engine needs to run optimally. That hurts performance and can trigger a MAP DTC. Be sure to check fuel pressure.

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 (1992-1997 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).