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 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,
Testing sensors and actuators (to include relevant circuit/connectors):
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.
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 3 pin MAP sensor
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:
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.
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