STEP/SEQUENCE
RESULT
WHAT TO DO NEXT
TM 9-2320-363-20-1
Section 4
TROUBLESHOOTING CHARTS
E. FLASH CODE: 54
J1587 CODE:
P84 12 - VEHICLE SPEED SENSOR FAULT
NOTE - This chart is only to be used if:
1)
All basic mechanical checks and physical inspections have been performed with no problem found, and
2)
Diagnosis of DDEC-III was started at step Start-1, pg 3-345.41 and you have now been referred here.
54-1
Identify Type of
Vehicle Speed Sensor
Used
Determine whether the VSS used
Type (1) sensor
Go to 54-2.
is either:
Type (1) is a magnetic pick-up
Type (2) sensor
Go to 54-10.
and may be one of the following:
transmission tailshaft
sensor
wheel rim sensor
mechanical speedometer
cable adaptor sender
generator
OR
Type (2) which outputs a
square wave signal and
requires wave signal and
requires the ECM to be
configured for this type of
signal, (see sketch), this
includes the (Allison
Transmission Electronic
Controls) electronic speedo
output.
NOTE:
Plug in DDR and check calibration configuration to determine that the correct configuration is on for
the type of signal being used.
54-2
Check for Open
Disconnect ECM vehicle
Less than or
Go to 54-4.
harness connector.
equal to 5 ohms.
Also disconnect the VSS
connector.
Install a jumper wire between
Greater than
The VSS signal line (ckt #556)
sockets A and B of the VSS
5 ohms or open.
or return line (ckt #557) is open.
harness connector.
Repair open. Then go to 54-30.
Read resistance between sockets
E2 (ckt #556) and E3 (ckt #557)
on ECM vehicle harness
connector.
*Not recommended with DDEC Ill.
Change 3 3-345.353
