New Holland CX720 Repair Manual page 1820

0449.3-ENGINE SPEED SENSOR, SHORTED TO HIGH SOURCE
(SERVICE TOOL FAULT CODE 149) (B.10.A.95.83 - G.30.B.54)
CX840
0449.3 - ENGINE SPEED SENSOR, SHORTED TO HIGH SOURCE (SERVICE TOOL FAULT CODE 149)
Context:
Engine enabled - Speed restricted to 1800 rev/min.
Cause:
Engine flywheel speed sensor fault
Possible failure modes:
1. Speed sensor faulty
2. Wiring to speed sensor faulty
Solution:
1. Check the engine speed sensor.
A. Using a suitable multi-meter check across the speed sensor terminals for a short circuit or an open circuit
and between each terminal for a short to ground. If any of the above conditions exist replace the engine
speed sensor. The sensor resistance value is 880 - 920 Ω between the terminals 1 and 2.
B. If the sensor appears to be okay continue with step 2.
2. Check the engine speed sensor to flywheel air gap. The gap should be 0.5-1.5 mm.
NOTE : The air gap is a set dimension determined by design and is not adjustable. The only reason the air
gap will be incorrect is if damage has occurred to either the speed sensor or flywheel or if the sensor has been
incorrectly installed.
A. Remove the engine flywheel speed sensor and inspect for damage or a build up of dirt. With the sensor
removed also inspect the flywheel for damage. If any damage is evident replace the component.
B. If the engine speed sensor to flywheel air gap is correct continue with step 3.
3. Check the wiring to the speed sensor.
A. With the keystart switch OFF, disconnect the engine speed sensor connector and connector X192 of the
engine ECU. Using a suitable multi--meter check for continuity between pin 2 of the speed sensor and pin
1 of the engine ECU connector. Also check for continuity between pins 1 and 3 of the speed sensor and
pin 13 of the engine ECU connector. If an open circuit is indicated trace the fault and repair the wiring as
required.
B. With the keystart switch OFF, and the engine speed sensor connector X207 and connector X192 of the
engine ECU still disconnected check for a short to ground on each of the speed sensor pins. If a short to
ground is indicated trace the fault and repair the wiring as required.
C. With the engine speed sensor connector and connector X192 of the engine ECU still disconnected, turn
the keystart ON, (not cranking), and check for a short to +12 V on each of the speed sensor pins. If a short
to +12 V is indicated trace the fault and repair the wiring as required.
D. With the keystart switch OFF, reconnect the engine ECU connector. Turn the keystart ON, (not cranking),
and check for a voltage of approximately 0.25 V at pin 2 of the speed sensor connector. If 0.25 V is not
indicated replace the engine ECU. E. If the wiring checks out okay and the fault still exists continue with
step 4.
4. Fuel injection pump assembly fault
NOTE : The fuel injection pump has an integral speed sensor which is not a serviceable item and may produce
this error if faulty.
POWER PRODUCTION - ENGINE
2 4/7/2006
B.10.A / 274