
RENR9348-01 137
Troubleshooting Section
i02450722
Engine Speed/Timing Sensor
Circuit - Test
SMCS Code: 1439-038-VF; 1912-038
System Operat
ion Description:
Use this procedure to troubleshoot any suspect
problems with
the following sensors:
•
Primary engine speed/timing sensor
•
Secondary engine speed/timing sensor
This procedur
e covers the following diagnostic codes:
•
190-08 Engine Speed abnormal
•
342-08 Secondary Engine Speed signal abnormal
Theengineuse
s two engine speed/timing sensors.
The primary engine speed/timing sensor detects the
reference for engine speed and timing from a timing
ring with a no
tched pattern that has been machined
onto a portion of the crankshaft gear. The signal from
the primary engine speed/timing sensor is also used
by the ECM as a
control reference during a timing
calibration.
The seconda
ry engine speed/timing sensor detects
the reference for engine speed and timing from a
timing ring with a notched pattern that has been
machined on
to a portion of the camshaft gear.
The Electronic Control Module (ECM) counts the
time betwe
en pulses that is created by the sensor as
each gear rotates in order to determine rpm. Timing
is provided by the unique pattern of notches in the
timing rin
g.
Under normal operation, the secondary engine
speed/tim
ing sensor is used to determine timing
for starting purposes. The secondary engine
speed/timing sensor is used to determine when
the pisto
n in the No. 1 cylinder is at the top of the
compression stroke. When the timing has been
established, the primary engine speed/timing sensor
is then us
ed to determine engine speed.
When the timing has been established, the ECM
trigger
s each injector in the correct fi ring order at the
correct time. The actual timing and duration of each
injection is based on engine rpm and on load.
If the engine is running and the signal from one
sensor is lost, no noticeable change in engine
perform
ance will be noticed. If the engine is running
and the signals from both sensors are lost, fuel
injection will be terminated and the engine will be
shut do
wn by the ECM.
The engine will start when only one sensor signal is
present. The en
gine will not start if the signals from
both sensors are lost.
Both sensors a
re magnetic sensors. The two sensors
are not interchangeable. If a sensor is replaced, a
timing calibration is not necessary.
If a replacement of the ECM is r equired, the ECM
parameters and the timing calibration can be
transferred
from the suspect ECM to the replacement
ECM. Timing calibration will not be necessary. This
feature requires the Caterpillar Electronic Technician
(ET) and this
feature is only possible if the existing
ECM can communicate with Cat ET. Use the “Copy
Configuration - ECM Replacement” feature on Cat
ET.
A timing calibration is necessary after the
ECM softwar
e has been updated. Refer to
Troubleshooting, “Engine Speed/Timing Sensor -
Calibrate” for information that is related to timing
calibrati
on.
Complete all of the following tasks when you
install a s
peed/timing sensor:
•
Ensure that an O-ring is installed on the sensor.
If the O-ri
ng is damaged or missing, replace the
O-ring.
•
Lubricate
the O-ring with oil.
•
Ensure that the sensor is fully seated into the
engine bef
ore tightening the bracket bolt.
•
Ensure that the electrical connector is latched.
•
Ensure that the harness is properly secured, and
ensure that each tie-wrap is placed in the correct
location
.