Glossary

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. PID: AP

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. PID: BARO (pressure)

CMP: CaMshaft Position 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. PID: RPM

DTC: Diagnostic Trouble Code
System malfuction 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. PID: EBP (pressure), EBP V (volts)

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, 1.37volts@176F, .96volts@205F. PID: EOT (degrees)

EPR: Exhaust backPressure Regulator, also EBP regulator
Output; For quicker engine warm-up at cold temperatures. If the IAT is below 37F (50F some models) and the EOT is below 140F (168 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 reapplys the EPR as load demand decreases until EOT or IAT rises. PID: EPR (duty cycle), EBP (pressure)

GPC: Glow Plug Control
Output; The PCM energizes the glow plug relay for 10 to 120 seconds depending on EOT and BARO. PID: GPC (time)

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. PID: GPL.

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. PID: GPML (left bank current), GPMR (right bank current), GPMC (relay output)

IAT: Intake Air Temperature sensor
Strategy input; The PCM uses this for EPR control. 5 volts in, 3.897volts@32F, 3.09@68F, 1.72@122F. PID: IAT (degrees)

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, 1.0volt@580psi, 3.22volts@2520psi. PID: ICP (pressure), ICP V (voltage)

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. PID: FuelPW Fuel Pulse Width signal from PCM (milliseconds)

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 fule pressure through the injector nozzels. PID: IPR (% of duty cycle), MFDES Mass Fuel Desired an internal PCM calculation based on load demand (MG)

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. PID: IVS (off/on)

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 monitor boost to limit fuel delivery to control maximum turbo boost. Frequency output; 111Hz=14.7psi, 130Hz=20psi, 167Hz=30psi. PID: MAP (pressure basline 14.7psi), MAP HZ (frequency), MGP Manifold Gauge Pressure (pressure base line 0psi) turbo boost

MAT:Manifold Air Temperature sensor
Strategy input; The PCM uses this signal to adjust fuel and timing. 99 model/year engines. PID: MAT

MIL: Malfuction 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 a 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 ouput signals from the PCM.

Useful PID comparisons
AP--Accelerator Pedal--and IVS--Idle Validation Switch: IVS should switch state when AP voltage is approximatly 0.2-0.3 volts higher than base idle position.

ICP--Injection Control Pressure--IPR--Injection Pressure Regulator--and MFDES--Mass Fuel Desired: ICP should rise as IPR duty cyle increases; MFDES and IPR should rise at the same rate as load and/or demand increases (actual readings may not match); ie. ICP=500psi, IPR=12%, MFDES=10MG @500 RPM; ICP=900psi, IPR=22%, MFDES=20MG @1800RPM/cruise; ICP=1800psi, IPR=50%, MFDES=40MG @3000RPM/hard accel.

ICP--Injection Control Pressure--and RPM--CaMshaft Position Sensor: After 3 minutes at 3300 RPM, ICP pressure should be below 1400psi for Federal, 1250psi for California Emmisions, and 1500psi for 99.5. At idle, ICP should be 550-700psi for Federal, 400-600 for California and stable.

V PWR--Battery Voltage--RPM--CaMshaft Position sensor--ICP--Injection Control Pressure--FuelPW--Fuel Pulse Width: When starting V PWR should be above 10volts, ICP should be at least 500psi, at least 100RPM, and FuelPW 1mS-6mS. Once the PCM recognizes CMP speed and cylinder ID, FuelPW should default to 0.42mS, 0.60mS for 99 up, until ICP reaches starting pressure.

EOT--Engine Oil--and IAT--Intake Air Temperatures: After a cold soak, before starting EOT and IAT should be within 10 degrees of each other, Key On Engine Off.

BARO--Barometric--MAP--Manifold Absolute--and EBP--Exhaust BackPressures: All three should indicate atmospheric pressure (14.7psi at sea level) and read within 0.5 psi of each other, Key On Engine Off.

ICP--Injection Control Pressure--and ICP V--ICP Voltage: ICP should read 0psi, ICP V should read 0.20-0.25 volts, Key On Engine Off.

EBP--Exhaust BackPressure--MGP--Manifold Gauge Pressure--and RPM--CaMshaft Position Sensor: At full throttle in neutral, EBP should be below 28psi; At full throttle in fourth (manual) or third (auto) gear, MGP should be 15psi.

The PCM reads only voltage signals from the sensors. All readings which are not displayed in volts are what the PCM calculates those sensor inputs equal. In some cases, the PCM uses one voltage input to calculate a base line for other sensor readings. For example, BARO is used to calculate MAP/MGP base line. At sea level, calculates BARO at 14.7 PSI, so a MAP reading of 14.7 equals 0 PSI MGP. At an elevation of 5000 feet, BARO and MAP would be 12.1 PSI, so the MGP base line would be recaluclated to reflect 0 and not -2.6 PSI.

All ouputs are functions that the PCM is attempting to perform based on the inputs it is receiving. If there is an output device malfunction, the results may not be what the PCM is trying to achieve, but the output signal may still show normal. Some outputs may not match actual measurements. For example, the displayed duty cycle of the IPR may not match the actual duty cycle as viewed on a scope, or the displayed transmission control pressure output may not match the actual pressure on a test gauge.

Strategic displays like MFDES will change as the PCM detects changes in sensor inputs which may indictae changes in environment, such as altitude, or wear in the engine. This is part of the PCM's adaptive strategy, or "learning" capability.

©
1999