How to Test the MAP Sensor with a Multimeter (Step by Step Guide)
Content
The intake manifold absolute pressure (MAP) sensor detects air pressure in the intake manifold and allows the vehicle to change the air/fuel ratio. When the MAP sensor is bad, it can degrade engine performance or cause the check engine light to come on. It uses vacuum to control intake manifold pressure. The higher the pressure, the lower the vacuum and output voltage. The higher the vacuum and the lower the pressure, the higher the voltage output. So how do you test the MAP sensor with a DMM?
This step by step guide will teach you how to test MAP sensors with DMMs.
What does the MAP sensor do?
The MAP sensor measures the amount of air pressure in proportion to the vacuum in the intake manifold, either directly or through a vacuum hose. The pressure is then converted into a voltage signal, which the sensor sends to the power control module (PCM), your car's computer. (1)
The sensor requires a 5-volt reference signal from the computer to return motion. Changes in vacuum or air pressure in the intake manifold change the electrical resistance of the sensor. This can increase or decrease the signal voltage to the computer. The PCM adjusts cylinder fuel delivery and ignition timing based on current load and engine speed using information from the MAP sensor and other sensors.
How to check the map sensor with a multimeter
No. 1. Preliminary check
Perform a pre-check before testing the MAP sensor. Depending on your setup, the sensor is connected to the intake manifold via a rubber hose; otherwise, it connects directly to the inlet.
When problems arise, the vacuum hose is most likely to blame. Sensors and hoses in the engine compartment are exposed to high temperatures, possible oil and gasoline contamination, and vibration that can impair their performance.
Inspect the suction hose for:
- twist
- weak ties
- cracks
- tumor
- softening
- hardening
Then inspect the sensor housing for damage and make sure the electrical connector is tight and clean and the wiring is in perfect working order.
The ground wire, signal wire, and power wire are the three most important wires for an automotive MAP sensor. However, some MAP sensors have a fourth signal line for the intake air temperature controller.
It was required that all three wires work properly. It is extremely important to check each wire individually if the sensor is faulty.
No. 2. Power wire test
- Set the voltmeter settings on the multimeter.
- Turn on the ignition key.
- Connect the red lead of the multimeter to the MAP sensor power lead (hot).
- Connect the black lead of the multimeter to the battery ground connector.
- The displayed voltage should be approximately 5 volts.
No. 3. Signal wire test
- Turn on the ignition key.
- Set the voltmeter settings on the digital multimeter.
- Connect the red wire of the multimeter to the signal wire.
- Connect the black lead of the multimeter to ground.
- Since there is no air pressure, the signal wire will read about 5 volts when the ignition is on and the engine is off.
- If the signal wire is good, the multimeter should show about 1-2 volts when the engine is turned on. The value of the signal wire changes because air begins to move in the intake manifold.
No. 4. Ground wire test
- Keep the ignition on.
- Install a multimeter on a set of continuity testers.
- Connect two DMM leads.
- Because of the continuity, you should hear a beep when both wires are connected.
- Then connect the red lead of the multimeter to the ground wire of the MAP sensor.
- Connect the black lead of the multimeter to the battery ground connector.
- If you hear a beep, the ground circuit is working properly.
No. 5. Intake air temperature wire test
- Set the multimeter to the voltmeter mode.
- Turn on the ignition key.
- Connect the red wire of the multimeter to the signal wire of the intake air temperature sensor.
- Connect the black lead of the multimeter to ground.
- The IAT sensor value should be about 1.6 volts at an air temperature of 36 degrees Celsius. (2)
Symptoms of a Failed MAP Sensor
How to tell if you have a bad MAP sensor? The following are important questions to be aware of:
Fuel economy not up to standard
If the ECM detects a low or no air level, it assumes the engine is under load, dumps more gasoline, and advances the ignition timing. This results in high gas mileage, poor fuel efficiency and, in extreme cases, an explosion (very rare).
Insufficient power
When the ECM detects a high vacuum, it assumes the engine load is low, reduces fuel injection, and retards ignition timing. In addition, fuel consumption will be reduced, which, apparently, is a positive thing. However, if not enough gasoline is burned, the engine may lack acceleration and driving power.
It's hard to start
Therefore, an abnormally rich or lean mixture makes it difficult to start the engine. You have a problem with the MAP sensor if you can only start the engine when your foot is on the accelerator pedal.
Emission test failed
A bad MAP sensor can increase emissions because fuel injection is not proportional to engine load. Excessive fuel consumption leads to an increase in hydrocarbon (HC) and carbon monoxide (CO) emissions, while insufficient fuel consumption leads to an increase in nitrogen oxide (NOx) emissions.
Take a look at some of our articles below.
- How to Use a Cen-Tech Digital Multimeter to Check Voltage
- How to test a 3 wire camshaft sensor with a multimeter
- How to check the ignition control unit with a multimeter
Recommendations
(1) PCM — https://auto.howstuffworks.com/engine-control-module.htm
(2) temperature – https://www.britannica.com/science/temperature
