Troubleshooting

(Table 103, contd)
Diagnostic Trouble Codes for the Engine Speed/Timing Sensors
J1939
Code
Description
Notes
723-8 Engine Speed Sensor #2 : Abnormal Frequency,
Pulse Width or Period
The Electronic Control Module (ECM) detects the following conditions:
A loss of signal from the secondary speed/timing sensor for four crankshaft
revolutions.
OR
An invalid signal from the secondary speed/timing sensor for one engine
revolution.
The engine is running.
The diagnostic code will be logged.
The loss of signal from the secondary speed/timing sensor will prevent the en-
gine from starting.
637-11 Engine Timing Sensor : Other Failure Mode The Electronic Control Module (ECM) detects the following conditions:
The outputs from the primary speed/timing sensor and the secondary speed/
timing sensor differ by more than 10 crankshaft degrees for at least four engine
revolutions.
The engine is running.
There is a valid signal from the secondary speed/timing sensor.
The engine uses two engine speed/timing sensors.
The primary speed/timing sensor is located on the
front left-hand side of the cylinder block. The primary
speed/timing sensor generates a signal by detecting
the movement of the teeth that are located on the
crankshaft timing ring. The signal that is generated
by the speed/timing sensor is transmitted to the
ECM. The ECM uses the signal from the speed/
timing sensor to calculate the position of the
crankshaft. The signal is also used to determine the
engine speed.
The secondary speed/timing sensor is located in the
front cover. The secondary speed/timing sensor
generates a signal that is related to the camshaft
position. The secondary speed/timing sensor detects
the movement of the position wheel on the front of
the camshaft. The signal that is generated by the
speed/timing sensor is transmitted to the ECM. The
ECM calculates the speed and the rotational position
of the engine by using the signal. The secondary
speed/timing sensor is required for starting purposes.
During normal operation, the secondary speed/timing
sensor is used to determine the cycle that the engine
is on. When the timing has been established, the
primary speed/timing sensor is then used to
determine the engine speed and the angular position.
The loss of signal to the primary sensor and/or the
secondary sensor will result in one of the following
faults:
• The engine will continue to run when only one
sensor signal is present from either the primary
sensor or the secondary sensor.
• Loss of signal from the primary sensor and the
secondary sensor during operation of the engine
will cause fuel injection to be terminated and the
engine will stop.
Pull-up Voltage
The ECM continuously outputs a pull-up voltage on
the circuit for the secondary speed/timing sensor
signal wire. This pull-up voltage is required for correct
sensor operation and diagnostics.
When the sensor is disconnected, this pull-up voltage
can be measured at the harness connector for the
sensor.
UENR0612-07 225
Circuit Tests
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