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Engine Sensors & What They Do
Courtesy of: dieselmann

AP Accelerator Pedal Position Sensor
Load/demand input; PCM uses this to determine mass fuel desired, adjusts fuel delivery through IPR duty cycle and fuel pulse width and injection timing; 5 volts in, 0.5-0.7 volts at idle, 4.5 volts at WOT.
BARO Barometric Pressure Sensor
Strategy input; PCM uses this to adjust fuel quantity and injection timing for optimum running and minimum smoke, also glow plug on time to aid starting at higher altitudes; 5 volts in, @ 4.6 volts/14.7 psi at sea level, decreasing as altitude increases.
CMP Camshaft Posistion Sensor
Strategy and load input; PCM uses this to monitor engine speed to determine engine state and load, and cylinder position in order to control timing and fuel delivery; Hall Effect sensor which generates a digital voltage signal; high: 12 volts, low: 1.5 volts.
DTC Diagnostic Trouble Code
System malfunction or fault codes stored in the PCM to aid in diagnosis.
EBP Exhaust Backpressure Sensor
Feedback input; PCM uses this to monitor and control EPR operation; 5.0 volts in, 0.8-1.0 volts/14.7 psi KOEO or at idle, increases with engine RPM/load, decreases as altitude increases.
EOT Engine Oil Temperature Sensor
Strategy input; PCM uses this for determining glow plug on time, EPR actuation, idle speed, fuel delivery and injection timing and adjusts as temperature increases; 5.0 volts in, 4.37 volts@32F, 1.37 volts @ 176F, .96 volts @ 205F.
EPR Exhaust Backpressure Regulator, also EBP Regulator
Output.  For quicker engine warm-up at cold temperatures.  If the IAT is below 37F (50F on some models) and the EOT is below 140F (168 on some models) the PCM sends a duty cycle signal to a solenoid which controls oil flow from the turbo pedestal.  This causes a servo to close a valve at the turbo exhaust outlet.  The PCM monitors the EBP input to determine if the EPR needs to be disabled to provide power for increased load, then reapplies the EPR as load demand decreases until EOT or IAT rises.
GPC Glow Plug Control
Output.  The PCM energizes the glow plug relay for 10 to 120 seconds depending on EOT and BARO.
GPL Glow Plug Light
Output.  The PCM controls the "Wait to Start" light independently from the GPC output.  1 to 10 seconds depending on EOT and BARO.
GPM Glow Plug Monitor
Feedback input.  On 1997 and newer California emission vehicles, the PCM monitors glow plug relay output voltage to determine if any glow plugs are burned out or if the relay is functioning.
IAT Intake Air Temperature Sensor
Strategy input.  The PCM uses this for EPR control.  5 volts in, 3.897 volts @ 32F, 3.09 volts @ 68F, 1.72 volts @ 122F.
ICP Injection Control Pressure Sensor
Feedback input.  The PCM monitors the high pressure oil system to determine if it needs to be increased if load demand increases.  It also uses this to stabilize idle speed.  Volts in: 1.0 volt @ 580 psi, 3.22 volts @ 2520 psi.
IDM Injector Driver Module
The PCM sends a Cylinder Identification and Fuel Demand Control signal to the IDM.  The IDM sends a 110 volt signal to the injectors.  It then grounds each injector as fuel is required for that cylinder.  Fuel Pulse width is increased to deliver more fuel.  The IDM sends a feedback signal to the PCM for fault detection.
IPR Injection Pressure Regulator
Output.  The PCM controls the high pressure oil system by varying the duty cycle of the IPR.  The IPR controls the oil bypass circuit of the high pressure pump.  0% = full return to sump (open valve), 100% = full flow to injectors (closed valve).  The PCM monitors the system with the ICP input.  The PCM can control fuel delivery to the injectors by increasing the IPR duty cycle which increases fuel pressure through the injector nozzles.
IVS Idle Validation Switch
Strategy input.  On-off switch that the PCM uses to identify required operating mode; idle or power.  0 volts at idle, 12 volts off idle.
MAP Manifold Absolute Pressure Sensor
Strategy and feedback input.  The PCM monitors manifold pressure to control fuel delivery in order to minimize smoke.  It also optimizes injection timing for detected boost.  It also monitors boost to limit fuel delivery to control maximum turbo boost.  Frequency output: 111Hz = 14.7 psi, 130Hz = 20 psi, 167Hz = 30 psi.
MIL Malfunction Indicator Lamp
"Check Engine" or "Service Engine" light that the PCM illuminates when certain system faults are present.
PCM Powertrain Control Module, also ECU or ECM for Electronic Control Unit or Module
The computer which monitors sensor inputs and calculates the necessary output signals to the engine control systems.  It also checks for readings outside of normal parameters and records trouble codes for these faults.
PID Parameter Identification, also Data Stream or Sensor Data
Sensor readings displayed to a scan tool that represent sensor readings to and output signals from the PCM.