The manifold absolute pressure (MAP) sensor on the 1990-1991 5.2L V8 Dodge Dakota can easily be tested without having to remove it from the throttle body.
In this tutorial, I'm gonna' show you how to test it with a multimeter and a vacuum pump. You'll be able to find out if the MAP sensor is bad or not in 3 test steps.
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAP (1990-1991 5.2L V8 Dodge Dakota) (at: autotecnico-online.com).
NOTE: This tutorial applies to the following vehicles since they use the exact same MAP sensor: 1990 and 1991 5.2L V8 Dodge Dakota.
Symptoms Of A Bad MAP Sensor
The 5.2L V8 engine in your Dodge Dakota is a speed-density fuel injection system. In layman's terms, this means that the fuel injection computer needs to know the engine load, the engine RPM, and the temperature of the air entering the engine to calculate the amount of air entering the engine.
Once the fuel injection computer figures this out (the amount of air entering the engine), it then can calculate the amount of fuel to inject into the engine.
Since the manifold absolute pressure (MAP) sensor is such a critical component of the engine management system, when it fails you're gonna' see one of the following trouble codes:
- Code 13: No Change In MAP From Start To Run.
- Code 14: MAP Sensor Voltage Too Low.
- Code 15: MAP Sensor Voltage Too High.
You're also going to see one or more of the following symptoms:
- Rough idle.
- 'Rotten egg' smell coming from the exhaust.
- Won't pass the state mandated emissions test.
- Bad gas mileage.
- Lack of power, rough idle, or hesitation.
- Engine cranks a long time before starting.
MAP Sensor Circuit Descriptions
The MAP sensor is a 3 wire type sensor. This means that it has a power wire, a Ground wire and a signal wire. The table below has a brief description of each:
| Terminal | Wire | Description |
|---|---|---|
| 1 | Violet with white stripe (VIO/WHT) | 5 Volts |
| 2 | Dark green with red stripe (DK GRN/RED) | MAP Signal |
| 3 | Black with light blue striped (BLK/LT BLU) | Ground |
The key to successfully diagnosing the MAP sensor as good or bad is to know that the MAP sensor reacts to vacuum that is being applied to it.
When the MAP sensor is powered up but it's not receiving vacuum, its voltage signal is around 4.5 to 4.7 Volts DC.
As vacuum is applied to the MAP sensor, it's voltage signal starts to decrease.
If the MAP sensor is bad, you'll notice that it's voltage signal does not decrease no matter the amount of vacuum that is applied to it.
TEST 1: Testing The MAP Sensor Voltage Signal
To find out if the MAP sensor is good or bad, we're gonna' start off by checking the MAP voltage signal the MAP sensor produces.
As we manually apply vacuum to the MAP sensor, the voltage signal it produces should decrease. Once this vacuum is released, the MAP voltage signal should increase back to around 4 to 4.7 Volts DC.
NOTE: If you don't have a vacuum pump you can use your mouth to apply vacuum to the MAP sensor. If you would like to buy a vacuum pump, check out this link: HTOMT 2 In 1 Vacuum Pump Test Set.
IMPORTANT: The manifold absolute pressure (MAP) sensor must remain connected to its electrical connector for this test to function properly. To be able to access the voltage inside the signal wire, you'll need to use either a back probe or a wire piercing probe. You can see an example of this tool here: Wire Piercing Probe.
Let's get started:
- 1
Connect your vacuum pump to the MAP sensor's vacuum inlet port.
NOTE: Reconnect the MAP sensor to its connector if you disconnected it. - 2
Place your multimeter in Volts DC mode.
- 3
Connect the red multimeter test lead to the DK GRN/RED wire of the MAP sensor's connector.
This wire is identified by the number 2 in the photo above.
Remember, the MAP sensor must remain connected to its 3 wire connector. - 4
Ground the black multimeter test lead directly on the battery negative (-) terminal.
- 5
Turn the key the ON position but don't start the engine. This will power up the MAP sensor and you should see a reading of around 4 to 4.7 Volts DC on your multimeter.
- 6
Now, apply vacuum to the MAP sensor with the vacuum pump (or your mouth). The voltage signal value should decrease.
If you're using a vacuum pump you'll see the following approximate values: At 5 in.Hg → 3.9 Volts. At 10 in.Hg → 3 Volts. At 15 in.Hg → 2.1 Volts. At 20 in.Hg → 1.2 Volts. - 7
Release the vacuum. Once released, your multimeter should show the original voltage value.
Repeat this test step several times making sure that each time the voltage decreases/increases as you apply/release vacuum.
Let's examine your test:
CASE 1: The MAP voltage signal decreased and increased as you applied and released vacuum. This is the correct test result.
This test result confirms that the MAP sensor is working correctly (not defective). It also lets you know that the MAP sensor is getting 5 Volts and Ground.
CASE 2: The MAP voltage signal DID NOT decrease/increase as you applied and released vacuum. This test result usually indicates that the MAP sensor is defective.
To find out, the next step is to see if the orange (ORG) wire is feeding the MAP sensor with 5 Volts DC. For this test go to: TEST 2: Making Sure The MAP Sensor Has 5 Volts.
CASE 3: The multimeter DID NOT register any voltage. This test result usually indicates that the MAP sensor is defective.
To find out, the next step is to see if the orange (ORG) wire is feeding the MAP sensor with 5 Volts DC. For this test go to: TEST 2: Making Sure The MAP Sensor Has 5 Volts.