(Table 226, contd)
Diagnostic Trouble Codes for the Digital Throttles
J1939 Code PDL Code
Code Description
(code descriptions may vary)
Comments
91-4 91-4
Accelerator Pedal Position 1 : Voltage Below
Normal
The ECM detects the following conditions:
The ECM has been powered for 3 seconds.
Diagnostic code 168-4 is not active.
There are no active 678 or 41 codes.
The setting for the lower diagnostic limit has been exceeded
for one second.
If equipped, the warning lamp will come on. The diagnostic
code will be logged.
91-8 91-8
Accelerator Pedal Position 1 : Abnormal Fre-
quency, Pulse Width or Period
The ECM detects the following conditions:
The signal frequency from the digital throttle position sensor is
equal to 0% or 100% for more than 2 seconds.
The ECM has been powered for at least 3 seconds.
Diagnostic codes 91-3 and 91-4 are not active.
There are no active 678 or 41 codes.
The ECM sets the Throttle Position to “0%” .
If equipped, the warning lamp will come on. The diagnostic
code will be logged if the engine is running. The diagnostic
code will not be logged if the engine is cranking.
Follow the troubleshooting procedure in order to identify the root cause of the fault.
If a fault occurs with the primary throttle, the engine
will use the secondary throttle until the fault is
repaired.
If a fault occurs with the secondary throttle, the
engine will use the primary throttle until the fault is
repaired.
If a functional throttle is not available, the following
conditions will occur:
• The engine will default to the limp home speed.
• If the engine speed is higher than the limp home
speed, the engine will decelerate to the limp home
speed.
• If the engine speed is lower than the limp home
speed, the engine speed will remain at the current
speed.
• The engine will remain at this speed while the
diagnostic code remains active.
• All inputs from the faulty throttle are ignored by the
ECM until the fault is repaired.
• All inputs from the repaired throttle will be ignored
by the ECM until the keyswitch has been cycled.
Digital Throttle Position Sensor
The digital throttle position sensor is used to provide
a digital throttle position signal to the ECM. The
sensor output is a constant frequency signal with a
pulse width that varies with the throttle position. This
output signal is referred to as either a duty cycle or a
pulse width modulated signal (PWM). This output
signal is expressed as a percentage between 0 and
100 percent.
The digital throttle position sensor is most likely to be
attached directly to the throttle assembly. The digital
throttle position sensor requires no adjustment.
The duty cycle at low idle and the duty cycle at high
idle can vary depending on the application. The
percent of duty cycle is translated in the ECM into a
throttle position of 3 to 100 percent.
The digital throttle position sensors are powered by
+8 VDC from the ECM. The supply voltage is from
J1: to the digital throttle position sensor connector.
426 UENR4469-36
Circuit Tests
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