Isuzu 4JA1 Workshop Manual page 441

DTC P1120 (Symptom Code E) (Flash Code 21)
Circuit Description
The accelerator pedal position (APP) sensor is mounted
on the intake throttle assembly. The engine control
module (ECM) uses the APP sensors to determine the
amount of acceleration or deceleration desired by the
person driving the vehicle via the fuel injection control.
The APP sensor has the following circuits.
• 5 volts reference circuit
• Low reference circuit
• APP sensor signal circuit
The ECM supplies 5 volts to the APP sensor on the 5
volts reference circuit. The ECM also provides a ground
on the low reference circuit. The APP sensor provides a
signal to the ECM on the APP sensor signal circuit,
which is relative to the position changes of the
accelerator pedal angle.
The idle switch is also mounted on the intake throttle
assembly. The idle switch is part of the APP sensor
assembly. The idle switch is a normally closed type
switch. When the accelerator pedal is released, the idle
switch signal to the ECM is low voltage.
If the ECM detects the APP sensor signal and the idle
switch out of correlation, this DTC will set.
Condition for Running the DTC
• The ignition switch is ON.
Step
1 Did you perform the Diagnostic System Check-
Engine Controls?
2 1. Turn ON the ignition, with the engine OFF.
2. Observe the Idle Switch parameter with the scan
tool while
accelerator pedal.
Does the scan tool indicate OFF when the
accelerator pedal is depressed and ON when the
accelerator pedal is released?
3 1. Turn OFF the ignition.
2. Disconnect the idle switch harness connector.
3. Turn ON the ignition, with the engine OFF.
4. Observe the Idle Switch parameter with the scan
tool while momentarily jumping 3-amp fused
jumper wire across the idle switch harness
connector between pins 1 and 2 of the E-23
connector.
Does the scan tool indicate ON when the circuit is
jumpered and OFF when the circuit is not jumpered?
Action
depressing and releasing
Engine Control System (4JH1) 6E-187
Condition for Setting the DTC
Either of following condition is met.
• The ECM detects APP sensor angle is less than
0.35%, then the idle switch is OFF for longer than
0.6 seconds.
• The ECM detects APP sensor angle is more than
8.7%, then the idle switch is ON for longer than 0.6
seconds.
Action Taken When the DTC Sets
• The ECM illuminates the malfunction indicator
lamp (MIL) when the diagnostic runs and fails.
• The ECM uses an engine speed substitution of
1400 RPM.
Condition for Clearing the MIL/DTC
• The ECM turns OFF the MIL when the diagnostic
runs and does not fail.
• 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 P1120 (Symptom Code E) (Flash Code 21)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views
Value(s)

the


Yes
Go to Diagnostic
System Check-
Go to Step 2 Engine Controls
Go to Step 10 Go to Step 3
Go to Step 9 Go to Step 4
No