Spicer TPCS Troubleshooting Guide - Manual (Page 24)

21
Service Codes
Group: 3C! (Codes 18, 76, 77)
Type: Speed Signal
Code Description
Group 3C! indicates a faulty speed sensor signal. In general,
the system is configured to accept speed signals from any
one of several sources (analog or digital; J1708/J1587,
J1939). In this standard configuration, a loss of speed signal
fault is indicated by code 18. In some specific instances, a
vehicle may be configured to only accept speed from a spe-
cific data link. In these cases, codes 76 (SAE J1708/J1587)
and code 77 (SAE J1939) may be used to indicate a speed
signal fault.
• A wiring or sensor connection.
• A misadjusted or faulty sensor.
• A missing data link speed signal. (J1939 or J1708/
J1587)
Note: These codes will occur if ECU power has been cycled 50
times and no speed signal is received. Fifty power
cycles can occur after 25 engine starts without moving
the vehicle, however the code will clear as soon as a
speed signal is received.
See "Troubleshooting Tips" for general guidelines on system
diagnostics.
System Mode Condition Possible Causes
(Listed in Likely Order of Occurrence)
Normal Operation No speed signal - ECU power cycled 50 times without vehicle being moved.
- Sensor disconnected or loose plug.
- Either speed sensor wire is open (broken wire).
- Either speed sensor wire is shorted to ground
(bare wire is touching the frame).
- Faulty speed sensor.
- Sensor actuation failure.
- Tang drive broken/disconnected on mechanical sensor.
- Gap not adjusted correctly on pole sensor.
- Sensor wires shorted together.
Speed Sensor
Harness Connector
A B
ECU Harness Connector
A B
G
3
2
1
A
A
B
B
C
C
C
D
D
D
E
E
E
F
F
F
G
G H J K
H
H
J
J
K
K