Isuzu 4JA1 Workshop Manual page 454

6E-200 Engine Control System (4JH1)
DTC P1520 (Symptom Code B) (Flash Code 47)
Circuit Description
The neutral switch is installed on the transmission gear
control box. When the gear position is neutral, the
switch is closed and the switch signal is provided to the
engine control module (ECM). If the ECM detects the
neutral switch signal is not changed from other than
neutral during the predetermined engine speed and
vehicle speed range, this DTC will set. This DTC runs
only manual transmission.
Condition for Running the DTC
• The ignition switch is ON.
• The engine speed is higher than 665 RPM.
• The vehicle speed is lower than 2 km/h (1.2 MPH).
• The clutch pedal is released after once depressed.
Condition for Setting the DTC
• The ECM detects that the neutral switch signal is
continuously OFF (other than neutral) during three
consecutive driving cycles.
Action Taken When the DTC Sets
• The ECM illuminates the malfunction indicator
lamp (MIL) when the diagnostic runs and fails.
Step
1 Did you perform the Diagnostic System Check-
Engine Controls?
2 1. Install the scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Observe the Neutral Switch parameter with the
scan tool while shift to neutral and other
positions.
Does the scan tool indicate ON when the position is
neutral and OFF when other than the neutral?
3 1. Turn OFF the ignition.
2. Inspect the ECM (10A) fuse (EB-4) in the engine
room fuse block.
Is the ECM (10A) fuse (EB-4) open?
4 Replace the ECM (10A) fuse (EB-4). If the fuse
continues to open, repair the short to ground on one
of the circuits that is fed by the ECM (10A) fuse (EB-
4) or replace the shorted attached component fed by
the ECM (10A) fuse (EB-4).
Did you complete the repair?
Action
Condition for Clearing the MIL/DTC
Important:
• Following conditions must be met two consecutive
driving cycles. (One driving cycle: Ignition switch
ON > Engine run > Ignition switch OFF for 10
seconds)
- The engine speed is higher than 665 RPM
- The vehicle speed is lower than 2 km/h (1.2
MPH)
- The clutch pedal is released after once
depressed
- Neutral position
- After the above procedure is done, a history
DTC clears after 40 consecutive driving cycles
without a fault. Or clear with the scan tool.
Diagnostic Aids
• If an intermittent condition is suspected, refer to
Intermittent Conditions in this section.
DTC P1520 (Symptom Code B) (Flash Code 47)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views
Value(s) Yes
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Go to Step 2
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Go to Diagnostic
Aids
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Go to Step 4
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Go to Step 13
No
Go to Diagnostic
System Check-
Engine Controls
Go to Step 3
Go to Step 5
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