Optimized: Ambient Air Pressure and Temperature Sensor for Engine Management System
18
ENGINE MANAGEMENT SYSTEM
8
DESCRIPTION AND OPERATION
SENSOR - AMBIENT AIR PRESSURE AND
TEMPERATURE (AAP)
The AAP sensor is located in the top of the air filter housing. It provides a voltage signal relative to ambient air
pressure to the ECM. The AAP sensor works on the piezo crystal principal. Piezo crystals are pressure sensitive
and will oscillate in accordance to changes in air pressure. The AAP sensor produces a voltage between 0 and 5
volts proportional to the pressure level of the air in the air filter housing. A reading of 0 volts indicates low pressure
and a reading of 5 volts a high pressure. The ECM uses this signal for the following functions.
•
To maintain manifold boost pressure.
•
To reduce exhaust smoke emissions while driving at high altitudes.
•
Control of the EGR system.
Inputs / Outputs
The ECM (C0158-8) supplies the AAP sensor (C0188-3) with a 5 volt feed on a pink/purple wire. The output signal
from the AAP sensor (C0188-2) is sent to the ECM (C0158-10) on a white/yellow wire. The AAP sensor is earthed
(C0188-1) via the ECM (C0158-30) on a pink/black wire.
The AAP sensor can fail, or supply an incorrect signal if one or more of the following occurs:
•
Sensor open circuit.
•
Short circuit to vehicle supply.
•
Short circuit to vehicle earth.
•
Contaminated sensor element.
•
Damaged sensor element.
•
Resistance in wiring harness.
In the event of an AAP sensor signal failure, any of the following symptoms may be observed:
•
Altitude compensation inoperative (engine will produce black smoke).
•
Active boost control inoperative.
•
Turbocharger boost pressure limited to 1 bar (14.5 lbf.in
2
).
•
EGR altitude compensation inoperative.
In the event of a AAP sensor failure, the ECM will use a fixed default value from its memory.
