The manifold absolute pressure (MAP) sensor, on your 1.5L Honda Civic, can easily be tested with just a multimeter. In other words, you don't need a scan tool to find out if it's bad or not.
In this tutorial I'll show you how to test the MAP sensor in action (but without the engine running), in a step-by-step way, so that you can have the certainty that the money you're gonna' spend on a new part will actually solve the problem.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAP (1.5L Honda Civic) (at: autotecnico-online.com).
Symptoms Of A Bad MAP Sensor
The fuel system on your 1.5L Honda Civic is a speed-density type. This, in layman's terms means that the fuel injection computer needs to know engine speed, manifold pressure, and intake air temperature to calculate the amount of air entering the engine and thus inject the correct amount of fuel.
Its the MAP sensor's job to report manifold pressure (vacuum) to your Civic's fuel injection computer. Due to the critical role the MAP sensor plays in your Civic's engine management, when it fails you'll see the following trouble code lighting up the check engine light on the instrument cluster:
- Code 3: MAP Sensor Circuit.
The MAP sensor has 3 wire sticking out of its connector. 2 of those 3 wires supply it with power and Ground. The 3rd wire is the one that carries the MAP signal back to the fuel injection computer. In the table below are the wire descriptions we need to know to be able to successfully test the MAP sensor.
|MAP Sensor Circuits
1992, 1993, 1994, 1995 1.5L Honda Civic DX/LX
|MAP Sensor Circuits
1992, 1993, 1994, 1995 1.5L Honda Civic CX
Where To Buy The MAP Sensor And Save
If you find, after testing the Civic's manifold absolute pressure (MAP), that it's fried, take a look at the links below. I think they'll save you some bucks:
NOTE: If you're not sure if the above MAP sensor fit your particular 1.5L Civic don't worry, once you get to the site, they'll make sure the sensor is the right one, if not, they'll find you the right one.
TEST 1: Testing The MAP Sensor Voltage Signal
As you're probably already aware, when the engine idles and manifold vacuum pressure is low, the MAP sensor produces a high voltage signal.
When manifold vacuum is high, like when you accelerate the engine, the MAP sensor produces a low voltage signal.
When a MAP sensor fails, it'll usually stay stuck at one specific voltage value irrespective of the amount of vacuum applied to it.
To get our MAP sensor diagnostic under way, we're gonna' dive right in and verify that the MAP sensor's voltage signal changes depending on the amount of vacuum we manually apply to the sensor with a vacuum pump.
If you don't have a multimeter and need to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing (at: easyautodiagnostics.com).
IMPORTANT: The MAP sensor needs to stay connected to its electrical connector for this test to work. You'll need to use a back-probe or a wire-piercing probe to measure the MAP signal voltage. To see what a wire-piercing probe looks like, go here: Wire Piercing Probe.
Here are the steps :
Remove the MAP sensor from the intake manifold.
Connect your vacuum pump to the MAP sensor's vacuum inlet port.
Reconnect the MAP sensor to its connector if you disconnected it.
Set your multimeter's selector to Volts DC mode.
Connect the red test lead to the WHT or PNK/WHT wire of the MAP sensor's connector.
Remember, the MAP sensor must remain connected to its 3 wire connector.
Connect the black multimeter test lead directly to the battery negative (-) terminal.
When everything is ready, turn the key to the ON position but don't start the engine. This will power up the MAP sensor and you should see a reading of 4.7 Volts DC on your multimeter.
Now, apply vacuum to the MAP sensor with the vacuum pump (or your mouth).
The voltage signal value should decrease as you apply vacuum to the MAP sensor.
Release the vacuum. Once released, your multimeter should show the original voltage value.
Apply and release vacuum to the MAP sensor several times to make sure that each time the voltage decreases/increases (as you apply/release vacuum).
Let's take a look at your test results:
CASE 1: The MAP voltage signal decreased and increased as you applied and released vacuum. This test result confirms that the MAP sensor is OK and not defective.
CASE 2: The MAP voltage signal DID NOT increase (and/or decrease) as you applied and released vacuum. This test result confirms the manifold absolute pressure (MAP) trouble code lighting up the check engine light on your 1.5L Honda Civic.
If I where in your shoes and to be sure that the MAP sensor has truly failed, I would still make sure that the MAP sensor is getting both power and Ground. To check for power on the LT GRN wire, go to: TEST 2: Verifying MAP Sensor Has 5 Volts And Ground.
CASE 3: The multimeter DID NOT register any voltage. This test result doesn't condemn the MAP sensor as bad just yet. Why?
Because the MAP sensor may be missing either power or Ground. So the next step is to check that the MAP sensor is getting power, go to: TEST 2: Verifying Throttle Position Sensor Has 5 Volts And Ground.