Dtc71 - Barometric Pressure Sensor Fault - Isuzu 4HL1 Workshop Manual

DTC71 - Barometric Pressure Sensor Fault

Circuit Description
The atmospheric (barometric) pressure sensor is
installed inside the ECM and converts the atmospheric
pressure into a voltage signal. The VIM calculates the
atmospheric pressure from this voltage signal and
sends the result to the ECM. The ECM uses this
atmospheric pressure to calibrate the fuel injection
quantity (altitude compensation).
DTC71 will be set when the signal voltage is
excessively high or low.
Major Faulty Event
• Generation of black smoke
Conditions for Setting the DTC
The atmospheric pressure sensor voltage deviates
from the range between 0.5 V and 4.5 V for 1 second.
Action Taken When the DTC Sets
• After the DTC is set, the ECM will illuminate the
CHECK ENGINE lamp (MIL).
• The ECM controls the powertrain based on the set
atmospheric pressure (100 kPa).
Conditions for Clearing MIL/DTC
When the system fails and the DTC is stored to the
ECM, even repairing the faulty portion will not clear the
DTC from the memory. To clear the DTC, conduct the
following steps.
1. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
2. Turn on the idle position switch for not less than 1
second but not more than 3 seconds. (Release the
accelerator pedal.)
3. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
Step
Perform the "On-Board Diagnostic (OBD)
System Check".
1
Was the OBD System Check performed?
Check the atmospheric pressure sensor
output voltage.
1. Starter switch "OFF", and install Tech 2.
2. Starter switch "ON" and display the
2
engine data.
3. Check the atmospheric pressure sensor
output voltage.
Was the voltage within range?
Action
Engine Control System 1A-157
4. Turn on the idle position switch for not less than 1
second but not more than 3 seconds. (Release the
accelerator pedal.)
5. Turn off the idle position switch for not less than 1
second but not more than 3 seconds. (Press the
accelerator pedal.)
6. After the above operations are properly completed,
the CHECK ENGINE lamp (MIL) illuminates for 3
seconds to report the memory is cleared.
7. Turn off the starter switch. Wait for 5 seconds and
turn on the starter switch again.
When Tech 2 has been connected to the vehicle, the
DTC can be cleared through the memory clear
operation with Tech 2.
Diagnostic Aids
Poor connection or damaged harness may cause
intermittents. Check for the following conditions and, if
the fault is detected, repair or replace the faulty portion.
• Poor connection
connectors for backed-out pins, improper mating,
broken locks, improperly formed or damaged pins,
and poor pin-to-wire connection.
• Damaged harness: Inspect the wiring harness for
rubbed-through wire insulation or wire broken
inside the insulator. If the harness appears to be
OK, observe the display on Tech 2 while moving
connectors and wiring harnesses related to the
sensor. A change in the display will indicate the
location of the fault.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
3. If the DTC is not detected, the possible cause is
intermittent (intermittent fault).
Value(s)
—
Go to Step 2
0.5 ~ 4.5 V
Go to Step 3
at VIM: Inspect
Yes No
Refer to OBD
System Check
and go to Step 2
Go to Step 4
harness