Manifold absolute pressure sensor voltage (turbo diesel)

The purpose of this test is to investigate the operation of an analog type Manifold Absolute Pressure (MAP) sensor on a turbo diesel engine during idle, free revving and overrun conditions. 

How to perform the test

View connection guidance notes.

  1. Use manufacturer's data to identify the MAP sensor output signal circuit.
  2. Connect PicoScope channel A to the 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. Operate the accelerator pedal fully allow the engine to rev to maximum then release the pedal.
  7. With your live waveform 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

This known good waveform has the following characteristics:

  • With the engine running at idle the waveform shows a stable output of 2.4 V.
  • At around 1.7 s the voltage increases as engine speed increases.
  • At 2.5 s the voltage peaks around 4.1 V, at the peak engine speed.
  • There is a gradual voltage decrease over 2.5 s as the engine returns to the original 2.4 V idle condition.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select Manifold absolute pressure sensor (analog).

Further guidance

MAP sensors, have two functions within an engine management system:

  • To measure the atmospheric pressure at key on
  • To measure the engine load

The sensor is mounted in the intake manifold and is usually a piezoelectric strain gauge.

MAP sensors have three electrical connections, usually designated as;

  • Pin 1 = reference voltage.
  • Pin 2 = earth circuit.
  • Pin 3 = output signal volts.

Typically, the sensor’s voltage output is proportional to the manifold air pressure.

On turbocharged engines manufacturers use sensors capable of measuring pressure both above and below atmospheric.

Note; the MAP sensor measures the absolute pressure in the intake manifold:

At sea level, atmospheric pressure averages about 1013 mbar or 101.3 kPa. Therefore, when the engine is off, manifold pressure measured by the MAP sensor will be 1013 mbar or 101.3 kPa.

Generally, MAP sensors fall into three pressure measurement categories;

  1. measurements from atmospheric up to around 1.5 bar (usually used on normally aspirated engines)
  2. measurements up to around 2.5 bar boost
  3. measurements up to around 3.5 bar boost

Modern diesel engine turbochargers can produce around 2.7 bar boost. Having the wrong type of sensor in the engine will send false data to the Engine Control Module (ECM), resulting in erratic/poor performance and possible engine damage.

Symptoms of a faulty MAP sensor;

  • Usually engine light on.
  • Erratic or rough idle.
  • Delay in acceleration.
  • Excessive fuel consumption and high emissions – sensor reads too high, engine over fuels.
  • Lack of power – sensor reads too low, insufficient fuel. Engine may run hot and will increase N0x emissions.

Remember these symptoms can also be manifested by engine intake and mechanical issues, blockages, leaks etc.

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

P1101 - Actual measured airflow from MAF, MAP, EGR, and TP is not within range of the calculated airflow

P1106 - Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent High Voltage

P1107 - Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent Low Voltage

GT010-EN

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

  • Large Dolphin/Gator Clips

    £10.00

Help us improve our tests

We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.

Add comment

Your email address will not be published. Required fields are marked *

Guided test: Manifold absolute pressure sensor voltage (turbo diesel)