Manifold air pressure - digital - voltage

The purpose of this test is to evaluate the correct operation of a digital MAP sensor based on the output voltage and frequency during engine idle, WOT and over-run conditions.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Use the vehicle wiring diagram to identify the signal circuit.
  2. Connect PicoScope to the vehicle.
  3. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  4. Select GO or press the space bar to see live data.
  5. Start the engine and carry out a Wide-Open Throttle (WOT) test.
  6. With your live waveform on screen select STOP or press the space bar to stop your capture.
  7. Turn off the engine.
  8. Use the WAVEFORM BUFFER and ZOOM tools to examine your waveform.

Example waveform

Waveform notes

The output from the external MAP sensor will show a square wave its frequency will be lower at idle than when the throttle is opened. The example waveform clearly demonstrates the output signal and when the frequency is also displayed can be compared against the model specification.

A higher frequency could result from any number of problems, but could be as simple as a split vacuum hose or incorrectly adjusted tappet clearances. Prolonged exposure to this higher frequency can result in damage to the catalytic converter.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select Manifold Absolute Pressure MAP sensor (digital)

Example MAP sensor

Further guidance

The MAP sensor is employed to measure the pressure in the inlet manifold, and it is this output that when sent back into the engine management system can determine either the fueling or the amount of vacuum, light load ignition advance. The MAP sensor will in most cases measure a negative pressure, but can also be used to measure a positive boost pressure on a vehicle equipped with a turbo charger.

The sensor is a 3 wire device that will have:

  • A 5 V supply voltage.
  • An earth connection.
  • A varying output that can be either analogue or digital.

This particular component can be either an integral part of the ECM or an individual component.

A digital map sensor will produce a square wave signal to the ECM, this square wave will change frequency with varying engine vacuum readings. 

Typical readings whilst testing a MAP Sensor:

Vacuum (inches Hg) Vacuum (mbar) Frequency (Hz)
29.6 1000 80
23.6 800 93
17.6 600 110
11.8 400 123
5.9 200 140
0 0 160


This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Premium 6-way breakout lead set


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • PicoScope Battery Clip


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Guided test: Manifold air pressure - digital - voltage