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ENGINE MANAGEMENT SYSTEM - TD5 DESCRIPTION AND OPERATION 18-1-11 Ambient Air Temperature and Pressure (AAP) sensor The AAP sensor is located in the top of the air filter housing. It provides voltage signals relative to both ambient air l To maintain manifold boost pressure. l To reduce exhaust smoke emissions while driving at high altitude. l Control of the EGR system. The sensor also supplies a voltage between 0v and 5v proportional to ambient temperature. The ECM uses this signal l Exhaust gas over temperature protection. l Turbocharger overspeed protection. Input/Output The AAP sensor can fail the following ways or supply incorrect signal: l Sensor open circuit. l Short circuit to vehicle supply. l Short circuit to vehicle earth. l Contaminated sensor element. l Damaged sensor element. l Resistance in wiring harness. In the event of an AAP sensor signal failure any of the following symptoms may be observed: l Altitude compensation inoperative (engine will produce black smoke). l Active boost control inoperative. l Turbocharger boost pressure limited to 1 bar (14.5 lbf.in 2 ). l EGR altitude compensation inoperative. The MIL will not illuminate in an AAP sensor failure, and the ECM will use a fixed default value from its memory. |