The purpose of this test is to investigate the operation of a combined Temperature sensor and Manifold Absolute Pressure (TMAP) sensor unit on a turbo diesel engine during idle, free revving, and overrun conditions.
These known good waveforms have the following characteristics:
Channel A illustrates the air pressure waveform:
Channel B illustrates the air temperature waveform:
There are no anomalies or drop-outs in either signal.
TMAP sensors fulfil the functions of standard MAP sensors. That is, they respond to the air pressure within the intake manifold and allow the Engine Control Module (ECM) to estimate two important parameters:
However, they also have an additional intake temperature sensor to help the ECM better estimate the air density within the intake manifold. On turbocharged vehicles, this is necessary as the air density and temperature are altered by the actions of both the turbocharger and the intercooler.
The sensor can be mounted on the manifold housing itself, on pipework between the manifold and the intercooler, or on the outlet of the intercooler.
The pressure sensing element is usually a piezoelectric strain gauge having a voltage output proportional to the manifold air pressure. Temperature monitoring uses a Negative Temperature Coefficient (NTC) thermistor (the sensor resistance decreases as temperature increases). Both sensors reference their output relative to a 5V supply voltage.
All TMAP sensors will have four electrical circuit connections:
Care should be taken during TMAP sensor testing, as the pressure and temperature signals are both analog and can be confused.
Symptoms of a faulty MAP sensor:
Possible failures that can cause erroneous MAP sensor signals are:
Selection of component related Diagnostic Trouble Codes (DTCs):
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