Manifold air pressure - petrol - analog - voltage

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

How to perform the test

View connection guidance notes.

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

Example waveform

Waveform notes

The Manifold Absolute Pressure (MAP) sensor measures the vacuum in the inlet manifold.

This output, when sent back to the engine management system, determines either the fuelling or the amount of vacuum (or light load) advance.

The sensor is a three-wire device with:

  • A 5 volt supply voltage
  • An earth connection
  • A varying analogue output
  • A vacuum connection to the inlet manifold

This component can be either an integral part of the electronic control module or an individual component. The output from the external sensor shows voltage that rises and falls depending upon the vacuum.

When the engine is stationary or the throttle is wide open, zero vacuum is present and the sensor output is about 5 volts. As a vacuum is applied, the voltage drops. The example waveform shows that, at idle, the output is about 1 volt. As the throttle is opened, the vacuum in the manifold drops and the output voltage rises. In this case the voltage rises to almost 5 volts.

The 'hash' on the waveform is due to the vacuum change from the induction pulses as the engine is running.

Voltages are similar between different manufacturers and a lower-than-anticipated voltage will produce a loss of power due to fuel starvation. Conversely a higher voltage will cause overfuelling and could eventually result in the failure of the catalytic converter if allowed to persist. This high voltage could result from any number of problems but may be as simple as a split vacuum hose or incorrectly adjusted tappet clearances. The voltage from an integral MAP sensor can only be evaluated by a Fault Code Reader (FCR) due to the lack of access to the output voltage.

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 (analog).

Further guidance

The Manifold Absolute Pressure (MAP) measures the pressure in the inlet manifold, and is sent back into the engine management system to determine either the fuelling or the amount of vacuum (light load) ignition timing advance. The MAP sensor in most cases measures 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 has:

  • A 5 volt supply
  • An earth connection
  • A varying output that can be either analogue or digital
  • A vacuum connection to the inlet manifold

This component can be either an integral part of the Electronic Control Module (ECM), or an individual component.

The output from the analogue version rises and falls depending upon the vacuum. When the engine is stationary or the throttle is wide open, zero vacuum is present and the output is about 5 volts. As a vacuum is applied this voltage will drop.

Diagnostic trouble codes

Selection of component-related Diagnostic Trouble Codes (DTCs):

P0105 - MAP Sensor Circuit Insufficient Activity.

P0106 - Manifold Absolute Pressure (MAP) System Performance.

P0107 - Manifold Absolute Pressure (MAP) Sensor Circuit Low Voltage.

P0108 - Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage.

P0109 - Manifold Absolute Pressure Circuit Intermittent.

GT024-2

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

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  • 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 - petrol - analog - voltage