Dtc P256A (Flash Code 31) - Isuzu 2008MY N Series Workshop Manual

1A-304 Engine Control System (4HK1)

DTC P256A (Flash Code 31)

Circuit Description
The idle up sensor controls the idle speed during warm
up and it is installed in the driver's side instrument
panel. This sensor is active only when the gear position
is in the neutral position. When the shift lever is moved
to another position, the signal is ignored. The ECM
receives the idle up signal from the idle up sensor and
controls the fuel injection quantity. The idle up sensor
has following circuits
• 5 volts reference circuit
• Low reference circuit
• Idle up sensor signal circuit
The idle up sensor provides a signal to the ECM on the
signal circuit, which is relative to the position changes
of the idle up sensor angle. If the ECM detects an
excessively low or high signal voltage, this DTC will set.
Condition for Running the DTC
• DTCs P060B and P0641 are not set.
• The battery voltage is between 18 to 32 volts.
• The ignition switch is ON.
Condition for Setting the DTC
Either of following condition is met:
• The ECM detects that the idle up sensor signal
voltage is less than 0.1 volts for longer than 3
seconds.
• The ECM detects that the idle up sensor signal
voltage is more than 4.9 volts for longer than 3
seconds.
Circuit/ System Testing DTC P256A
Step
Did you perform the Diagnostic System Check
1
- Engine Controls?
1. Install a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Fully turn the idle up sensor between lowest
position (full counterclockwise direction) and
2
highest position (full clockwise direction) while
observing the Idle Up Sensor parameter with a
scan tool.
Does the scan tool indicate within the
specified value during turning the sensor?
Monitor the DTC Information with a scan tool.
3
Is DTC P0641 also set?
Is the Idle Up Sensor parameter less than the
4
specified value at Step 2?
Action
Action Taken When the DTC Sets
• The ECM illuminates the SVS lamp when the
diagnostic runs and fails. Refer to DTC Type
Definitions for Action Taken When the DTC Sets -
Type C. (Euro 4 specification)
• The ECM illuminates the MIL when the diagnostic
runs and fails. Refer to DTC Type Definitions for
Action Taken When the DTC Sets - Type A.
(Except Euro 4 specification)
• The ECM disables idle up sensor control.
Condition for Clearing the DTC
• Refer to DTC Type Definitions for Condition for
Clearing the SVS Lamp/ DTC - Type C. (Euro 4
specification)
• Refer to DTC Type Definitions for Condition for
Clearing the MIL/ DTC - Type A. (Except Euro 4
specification)
Diagnostic Aids
• If an intermittent condition is suspected, refer to
Intermittent Conditions in this section.
• Idle up sensor may have an intermittent open
somewhere in the operating range.
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or ECM Connector End Views
Value(s) Yes
—
Go to Step 2
0.2 to 4.8
volts
Go to Diagnostic
Aids
—
Go to Step 4
0.1 volts
Go to DTC P0641
No
Go to Diagnostic
System Check -
Engine Controls
Go to Step 3
Go to Step 5
Go to Step 8