Dtc P0502 Or P0503 (Flash Code 25) - Isuzu 2008MY N Series Workshop Manual

1A-200 Engine Control System (4HK1)

DTC P0502 or P0503 (Flash Code 25)

Circuit Description
Model without ABS
The vehicle speed sensor (VSS) is used by the ECM
and speedometer, which generates a speed signal from
the transmission output shaft rotational speed. The
sensor has the following circuits.
• Ignition voltage feed circuit
• Low reference circuit
• VSS signal circuit
The VSS uses a hall effect element. It interacts with the
magnetic field created by the rotating magnet and
outputs square wave pulse signal. The ECM calculates
the vehicle speed by the VSS. If the ECM detects VSS
signals are not generated, DTC P0502 or P0503 will
set.
Model with ABS
The EHCU calculates the vehicle speed based on the
signal from the wheel speed sensors. The ECM
receives the pulse signal from the EHCU. If the ECM
detects that vehicle speed signal from the EHCU are
not generated, this DTC will set.
Condition for Running the DTC
• DTC P060B is not set.
• The battery voltage is between 18 to 32 volts.
• The ignition switch is ON.
Circuit/ System Testing DTC P0502 (Model without ABS)
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.
2
4. Monitor the DTC Information with a scan tool.
Does the DTC fail this ignition?
1. Turn OFF the ignition.
2. Disconnect the VSS harness connector.
3. Turn ON the ignition, with the engine OFF.
3 4. Connect a test lamp between the ignition
voltage feed circuit (pin 1 of J-48) and a
known good ground.
Does the test lamp illuminate?
Connect a test lamp between the signal circuit (pin
3 of J-48) and battery voltage.
4
Does the test lamp illuminate?
Action
Condition for Setting the DTC
• The ECM detects that the VSS signal voltage is
less than 0.5 volts. (DTC P0502)
• The ECM detects that the VSS signal voltage is
more than 20 volts. (DTC P0503)
Action Taken When the DTC Sets
• 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.
• The ECM limits fuel injection quantity.
Condition for Clearing the DTC
• Refer to DTC Type Definitions for Condition for
Clearing the MIL/ DTC - Type A.
Diagnostic Aids
• If an intermittent condition is suspected, refer to
Intermittent Conditions in this section.
• An aftermarket signal pulse pickup device may
affect intermittent condition.
Notice: If this DTC set, the Vehicle Speed parameter
on the scan tool will display 10 km/h (6 MPH).
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
—
Go to Step 3
—
Go to Step 4
—
Go to Step 7
No
Go to Diagnostic
System Check -
Engine Controls
Go to Diagnostic
Aids
Go to Step 6
Go to Step 5