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

1A-184 Engine Control System (4JJ1)

DTC P0502 or P0503 (Flash Code 25)

Circuit Description
Model without ABS
The vehicle speed sensor (VSS) is used by the ECM
and other modules, 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 an
improper voltage level on the signal circuit, DTC P0502
or P0503 will set.
Model with ABS
The EHCU calculates the vehicle speed based on the
signal from the each wheel speed sensor. The ECM
and other modules receive the vehicle speed pulse
signal from the EHCU. If the ECM detects an improper
voltage level on the signal circuit, DTC P0502 or P0503
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. Turn ON the ignition, with the engine OFF.
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 J48) and a known
good ground.
Does the test lamp illuminate?
Connect a test lamp between the signal circuit (pin
3 of J48) and battery voltage.
4
Does the test lamp illuminate?
Action
Condition for Setting the DTC
• The ECM detects that the vehicle speed signal
voltage is less than 0.5 volts. (DTC P0502)
• The ECM detects that the vehicle speed 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.
• The ECM inhibits pre injection.
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).
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