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ABS Speed Sensor
Air Flow Meter / Sensor
Air Intake Pressure Sensor
Alternator Current and Voltage
Amplifier Earth
Camshaft Sensor
Carbon Canister Solenoid Valve
Crankshaft sensor
Coolant Temperature sensor
Diesel Glow Plugs
Digital ECM to Ignition Amplifier Signal
Distributor Pickup
Dual Trace
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Exhaust Gas Recirculation
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Lambda Sensor
MAP Sensor
Primary
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MAP Sensor - Analogue Diagnostics
(scroll for MAP Sensor - Digital)

The Manifold Absolute Pressure (MAP) sensor is employed to measure the vacuum in the inlet manifold.

It is this output that when sent back to the engine management system can determine either the fuelling or the amount of vacuum (or light load) advance.

This particular component can be either an integral part of the electronic control module or an individual component. The output from the external sensor will show a rise and fall voltage depending upon the vacuum seen.

When the engine is stationary or the throttle is wide open, zero vacuum will be recorded and a low voltage will be seen, as a vacuum is applied the voltage will reduce.

All voltages are similar between different manufacturers and a lower than anticipated voltage will produce a loss of power due to fuel starvation and conversely a higher voltage will cause over fuelling and could eventually result in the failure of the catalytic converter if subjected to long term abuse. 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.


MAP Sensor - Digital Diagnostics


The Manifold Absolute Pressure (MAP) sensor is employed to measure the vacuum in the inlet manifold.

It is this output that when sent back to the engine management system can determine either the fueling or the amount of vacuum (or light load) advance.

The sensor is a three wire device which will have:
A 5 volt supply voltage
An earth connection
A varying frequency output (Hz)
A vacuum connection to the inlet manifold


This particular component can be either an integral part of the electronic control module or an individual component.

The output from the external MAP sensor will be lower at idle than when the throttle is opened.
Technical Information

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.

A digital map sensor will produce a square wave signal to the engine management ECM, this square wave will change frequency with varying engine vacuum readings. This output waveform can also be monitored on an oscilloscope, or the frequency measured on certain multimeters that have the appropriate setting (Hz).

MAP Sensor.

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