JLG 450A II Series, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3121290 – JLG Lift – 3-169
DTC 9999- Throttle Actuator Failsafe Spring Failure
• Throttle Actuator
• Check Condition- Key Off, Engine Stopped
• Fault Condition- When key is off (or actuator is unpow-
ered), the ECM is expecting failsafe spring in actuator to
return throttle position to near 0%. If throttle does not
reach this position when actuator is powered, a fault is
generated.
• Corrective Action(s)- Illuminate MIL, sound audible warn-
ing or illuminate secondary warning lamp. Govern engine
speed to a forced idle speed.
• Non-emissions related fault
Throttle actuator has a return spring that causes throttle to
move to a near 0% position when powered off. This causes
engine shutdown following a key off. If ECM detects throttle
position to be above x volts when key is off (as determined by
diagnostic calibration), it will power up the actuator and
attempt to drive it to a zero position. This should ensure
engine is stopped.
Fault sets if throttle does not return to a near 0% position with
key OFF.
Diagnostic Aids
• Disconnect throttle actuator from wire harness. Remove
throttle actuator from engine and manually move it. Verify
internal spring forces throttle back to near 0% position.
• Inspect throttle arm or fuel rack on fuel pump. Verify it is
not stuck.
E le c tro n ic T h ro ttle A c tu a to r w /Se ria l P o s itio n F e e db a c k
2
1 6 1 3 1 2
1
5 V _e x t V s = + 5 V DC 5 V _ rtn T P S 1 T P S S ER +
+ -M o to r D B W- D B W+
E C M
H -B rid g e
1 9 T P S S ER - S e ria l x m itte r
Electronic Throttle
Actuator w/Serial
Position Feedback
2
16
13
12
1
5V_ext
Vs=+5 VDC
5V_rtn
TPS1
TPS SER +
+
-
Motor
DBW-
DBW+
ECM
H-Bridge
19
TPS SER -
Serial
xmitter