Symptoms of a Bad or Failing Manifold Absolute Pressure Sensor (MAP Sensor)

The Manifold Absolute Pressure (MAP) sensor is used by the Powertrain Control Module (PCM) for engine load input. The PCM uses this input, as well as others, to calculate the correct amount of fuel to inject into the cylinders.

The MAP sensor measures the absolute pressure inside the intake manifold of the engine. At sea level, atmospheric pressure is about 14.7 psi (pounds per square inch). When the engine is off, the absolute pressure inside the intake equals atmospheric pressure, so the MAP will indicate about 14.7 psi. At a perfect vacuum, the MAP sensor will read 0 psi. When the engine is running, the downward motion of the pistons create a vacuum inside the intake manifold (For the purposes of engine control, when a technician says vacuum, what they are really saying is pressure that is less than atmospheric pressure). With a running engine, intake manifold vacuum usually runs around 18 - 20 “Hg (inches of mercury). At 20 “Hg, the MAP sensor will indicate about 5 psi. This is because the MAP sensor measures “absolute” pressure, based on a perfect vacuum, rather than atmospheric pressure.

A failed MAP sensor has serious implications on fuel control, vehicle tailpipe emissions and fuel economy. Symptoms of a bad or failing MAP sensor include:

1. Excessive fuel consumption

A MAP sensor that measures high intake manifold pressure indicates high engine load to the PCM. This results in an increase of fuel being injected into the engine. This, in turn, decreases your overall fuel economy. It also increases the amount of hydrocarbon and carbon monoxide emissions from your vehicle to the surrounding atmosphere. Hydrocarbons and carbon monoxide are some of the chemical components of smog.

2. Lack of power

A MAP sensor that measures low intake manifold pressure indicates low engine load to the PCM. The PCM responds by reducing the amount of fuel being injected into the engine. While you may notice an increase in fuel economy, you will also notice that your engine isn’t as powerful as it was before. By reducing the fuel into the engine, combustion chamber temperatures are increased. This increases the amount of NOx (oxides of nitrogen) production within the engine. NOx is also a chemical component of smog.

3. Failed emissions test

A bad MAP sensor will cause your vehicle to fail an emissions test. Your tailpipe emissions may show a high level of hydrocarbons, high NOx production, low CO2, or a high level of carbon monoxide.

A properly trained technician like those at YourMechanic are capable of diagnosing and repairing a failed MAP sensor.


Next Step

Schedule Vehicle Engine Electrical Inspection

The most popular service booked by readers of this article is Vehicle Engine Electrical Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Vehicle Engine Electrical Inspection reviews

Excellent Rating

(11)

Rating Summary
11
0
0
0
0
11
0
0
0
0

James

30 years of experience
790 reviews
James
30 years of experience
GMC Terrain L4-2.4L - Vehicle Engine Electrical - Windermere, Florida
very profesional,he did explain items properly

Ronnie

30 years of experience
72 reviews
Ronnie
30 years of experience
Dodge Charger V6-3.5L - Vehicle Engine Electrical Inspection - Nashville, Tennessee
He did a great job with my car and fixed some issues I couldn't figure out for awhile now!

Miguel

21 years of experience
203 reviews
Miguel
21 years of experience
Kia Optima L4-2.0L Turbo - Vehicle Engine Electrical Inspection - Nutley, New Jersey
I am so happy and grateful for meeting and having Miguel as my mechanic. I'm 64 yrs old and I have experienced many disappointments with car mechanics. Miguel is a blessing. I know when I meet a man with integrity, and has great intelligence. Thank you so much Miguel!!!

Caz

17 years of experience
104 reviews
Caz
17 years of experience
Toyota Solara V6-3.0L - Vehicle Engine Electrical Inspection - Acworth, Georgia
He was very honest. Nice guy. I will try to get him to come to my next appointment. Thanks!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

How to Replace a Fuel Pump Shut Off Switch
The fuel pump shut off switch may be faulty when the Check Engine Light comes on or if the engine suddenly turns off while driving.
Symptoms of Bad or Failing Fuel Injector O Rings
Common signs include an odor of fuel in the car, fuel leaks, and the Check Engine Light coming on.
How Long Does a Main Relay (Computer/Fuel System) Last?
Common signs include the engine not starting, inability to stay running for a long time, and no communication with scan tools.

Related questions

Will not accelerate beyond 65 mph

All vehicles have serviceable fuel filters, in fact your vehicle has 4 or more such filters. That is, EACH fuel injector has its own miniature filter basket so there are 4 potentially pluggable filters right there. There are some obvious...

Car passed inspection but when I took it in I was told it never should have passed.

Hi there. Different people who check the emissions on a vehicle may only check the computer and the gas cap. They may not check under the vehicle for any signs of fuel leakage. That is probably why the vehicle passed....

Stalling, issues with the vapor canister and with adding fuel

Hello. The symptoms you describe can be caused by many things. If your vapor canister is having known issues then I would start there, as the vapor canister is tied into the vehicle's fuel system and can affect its performance....

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com