Manifold air pressure - digital - voltage

The purpose of this test is to investigate the operation of a digital Manifold Air Pressure (MAP) sensor under varied engine operating conditions.

How to perform the test

View connection guidance notes.

  1. Use the vehicle wiring diagram to identify the MAP sensor output signal circuit.
  2. Connect PicoScope Channel A. to the MAP sensor output signal circuit.
  3. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
  4. Start the scope to see live data.
  5. Start the engine and fully depress the accelerator pedal until maximum RPM then release the pedal.
  6. With your waveforms on screen stop the scope.
  7. Turn off the engine.
  8. Use the Waveform Buffer, Zoom and Measurements 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

GT025-2

Disclaimer
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

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • PicoScope Battery Clip

    £2.75

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Guided test: Manifold air pressure - digital - voltage