Otherwise known as the pressure sensor, the F150 MAP Sensor is what you engine computer relies on to know how much air is heading into your engine. The MAP sensor is also known as the manifold absolute pressure sensor. Mounted into the engine bay, this sensor is connected to your intake manifold by a vacuum hose. It’s connected to a three pin engine harness and over time this F150 MAP sensor can foul on you or fail completely.
Today I’ll be showing you how to test the F150 MAP sensor in a 1996 Ford truck. This truck is a half ton truck with a 5.8 liter engine, and has a check engine light on for the pressure sensor.
There’s one of two ways you can check the trouble code in this truck, if you happen to own a OBDI version of this vehicle the code is very different than the five digit OBDII code.
Trouble codes for a bad F150 MAP sensor
Although one of the more obvious signs of your F150 having problems is your trouble code light, it can also be hard to start. Failed MAP sensor in your Ford truck can cause starting problems with your F150. Your idle will also suffer and your gas mileage will be very bad.
The trouble codes for this particular failed part vary, here’s just a few below :
- Code 22: MAP Sensor Out of Range
- Code 72: Insufficient MAP Change During Dynamic Response Test
- Code 128: MAP Sensor Vacuum Hose Damaged or Disconnected
In order to test your MAP sensor, you’ll need to use a digital multimeter. Once you are ready to test your Ford F150 MAP unit, insert your ignition key and turn to the “ON” position. This powers up the sensors in your engine bay, and allows you to check for operation.
Testing your Ford F150 MAP Sensor
Locate your F150 MAP sensor by tracing back the vacuum hose from your intake manifold. Now disconnect the three pin wiring harness, and you’ll be checking the ENGINE harness side of the plug.
The three wires are power ground and the signal wires to your manifold pressure sensor. Testing your F150 MAP Sensor for power is the first wire to check for, and to begin we’ll be using the multimeter. Put the black lead of your multimeter on the negative terminal of your battery, and you’ll be gently probing the ENGINE harness for power.
Testing the F150 MAP Sensor for Power
Now that you’ve got the manifold pressure sensor disconnected, you can begin testing. The first wire we’ll begin with is the switched power signal from your engine computer. This wire is the one that leads to PIN A on your three pin connector.
There should be 5 volts at this wire, which is the left most pin when you are facing the back of the harness.
The next wire to check at the engine harness is the low reference wire. The ground wire is the one that leads to PIN C.
Because both power and ground to your F150 MAP sensor are supplied by your engine computer, make sure to avoid crossing the two. If you accidentally cross power or ground you run the risk of burning out your Powertrain Control Module. If your pressure sensor is getting power and ground but your F150 truck isn’t running right, you need to test the signal wire.
Using a vacuum hand pump to test signal
Automotive hand pumps can apply vacuum to the inlet of your Ford MAP sensor. This replicates the operation of your engine, because when your 5.8 liter engine starts the engine creates vacuum at the MAP sensor inlet. To do this you’ll need to disconnect the vacuum line to your intake manifold and put it to the vacuum hand pump.
You’ll need to reconnect your F150 MAP sensor for this part of the DIY tutorial. Once the harness is connected, you’ll need to pierce the middle wire or the wire that leads to PIN B. Turn the dial of your multimeter to read Hertz or Hz. Your manifold absolute pressure sensor reads the vacuum at the intake manifold and send this Hertz signal to your engine computer.
Leave the F150 ignition turned to the ON position but do not start the engine. With your multimeter lead pierced you can read the signal being sent from your MAP sensor. Read the voltage signal with no change to pressure first, and the reading at PIN B should be around 152 Hz.
Now apply 5 in. Hg of vacuum and this reading should lower to 141 Hz. Increase the vacuum to 10in. Hg and the reading should hover around 127 Hz. Now raise the vacuum at the MAP inlet to 15 in. Hg which should lower the signal to 114 Hz.
If your Ford F150 MAP sensor doesn’t respond with these values, you need a replacement MAP. Remember that these values are an estimate and that your sensor will most likely vary a tad. If you have any more questions about this DIY tutorial on testing your F150 MAP Sensor, leave us a comment below and let us know!
