Acceleration control for the diesel engine is achieved via an
electronic throttle drive by wire system. The throttle is electronically
connected to the ECM and the ECM then controls the fuelling for the relevant
throttle demand signal from the Accelerator Pedal Position sensor (APP).
Electronic Engine Controls (303-14C Electronic Engine
Controls - 2.7L Diesel)
ELECTRONIC THROTTLE
Electronic Throttle
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The electric throttle controls the air flow into the engine. In
addition to the normal engine power control function, the electric throttle
allows the cruise control, idle speed control and engine speed limiting
functions to be performed without the need for additional hardware.
The
electric throttle consists of a throttle body which incorporates a throttle
plate driven by a DC motor via reduction gears. A return spring biases the
throttle plate in the closed direction.
Operation of the DC motor is
controlled by the ECM, which outputs two Pulse Width Modulated (PWM) signals to
an H bridge drive circuit in the motor. The ECM varies the speed and direction
of the motor by varying the duty cycle of the PWM signals.
To enable
closed loop control, the position of the throttle plate is supplied to the ECM
by two feedback Hall effect sensors in the throttle body. The feedback sensors
have a common 5 volt supply and a common ground connection from the ECM, and
produce separate linear signal voltages to the ECM proportional to the position
of the throttle plate. The ECM uses the signal from feedback sensor 1 as the
primary signal of throttle plate position, and the signal from feedback sensor 2
for plausibility checks.
- The signal from feedback sensor 1 varies between 0.5 volt (0% throttle
open) and 4.5 volts (100% throttle open)
- The signal from feedback sensor 2 varies between 4.5 volts (0% throttle
open) and 0.5 volt (100% throttle open)
While the ignition is on, the
ECM continuously monitors the two feedback sensors for short and open circuits
and checks the feedback sensor signals, against each other and the inputs from
the Accelerator Pedal Position (APP) sensor, for plausibility. If a fault is
detected in the feedback sensor signals or the DC motor, the
ECM:
- Stores a related fault code in memory.
- Illuminates the SERVICE ENGINE warning lamp in the instrument pack.
- Adopts a throttle limp home mode or disables throttle control, depending
on the nature of the fault.
The throttle limp home mode adopted
depends on the nature of the fault:
- If there is a fault with one feedback sensor, or the throttle position
controller in the ECM, the ECM limits vehicle acceleration by limiting
throttle plate opening.
- If there is a fault with both feedback sensors, the ECM uses fuel
injection cut-off to limit engine speed to 1300 rev/min maximum.
C0272 Electronic Throttle Pinout Details
Pin No |
Description |
Input/ Output |
1 |
Supply voltage |
Input |
2 |
Throttle position |
Output |
3 |
Throttle position + |
Input |
4 |
Throttle position - |
Input |
5 |
N/C |
- |
6 |
Signal ground |
- |
ACCELERATOR PEDAL POSITION SENSOR
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The Accelerator Pedal
Position Sensor (APP) is integral to the accelerator pedal assembly.
The
APP sensor enables the ECM to determine the throttle position requested by the
driver on the accelerator pedal.
The APP sensor is installed on the pedal
box and consists of a twin track potentiometer with wipers driven by a linkage
connected to the accelerator pedal. Each potentiometer track has a 5 volt supply
and ground connection from the ECM, and produces a linear signal voltage to the
ECM proportional to the position of the accelerator pedal. The signal voltage
from track 1 of the potentiometer is approximately double that of the signal
voltage from track 2.
From the sensor signals, the ECM determines driver
demand as a percentage of pedal travel, where 0% is with the pedal released and
100% is with the pedal fully depressed. Driver demand is then used to calculate
throttle angle, fuel quantity and ignition timing. The ECM also outputs driver
demand on the CAN system, for use by the brake and gearbox control
systems.
The ECM stores the signal values that correspond with closed and
wide open throttle, and adapts to new values to accommodate component wear or
replacement.
The signals from the APP sensor are monitored by the ECM for
short and open circuits and plausibility. If a fault is detected, the
ECM:
- Stores a related fault code in memory.
- Illuminates the SERVICE ENGINE warning lamp in the instrument pack.
- Inhibits the driver demand message on the CAN bus, which disables the Hill
Descent Control (HDC) function of the ABS modulator and reduces the
performance of the automatic gearbox (harsh gear changes and loss of kick
down).
- Adopts a throttle limp home mode.
The throttle limp home mode
adopted depends on the nature of the fault:
- If a fault is detected with one potentiometer track, the ECM limits
vehicle acceleration by limiting throttle plate opening.
- If a fault is detected with both potentiometer tracks, the ECM uses the
throttle plate to run the engine at a fixed speed of 1472 rev/min while the
brake pedal is released, and idle speed (750 rev/min) while the brake pedal is
pressed or if there is a brake pedal sensor fault.
- If there is a process fault in the ECM, the ECM either uses fuel injection
cut-off to limit engine speed to 1300 rev/ min or disables fuel injection to
stop the engine.
Accelerator Pedal Position Sensor Pin Out Table
Pin No |
Description |
Input/Output |
1 |
APP 1 ground |
- |
2 |
APP 1 signal |
Output |
3 |
APP 2 ground |
- |
4 |
N/C |
- |
5 |
APP2 Signal |
Output |
6 |
APPS 2 reference voltage |
Input |
7 |
APP 1 reference voltage |
Input |
8 |
N/C |
- |