Spicer CTIS (Central Tire Inflation System) Troubleshooting Guide - Manual (Page 55)

52
Service Codes
Speed Signal (Codes 18,
76, 77)
Speed Signal (Code 18, 76, 77)
Replace ECU.
Note: ECUs are not a typical cause of problems. If an
ECU is replaced, the system should be carefully
rechecked to make sure the problem has been fixed
and does not reoccur.
Yes
This fault is set because the ECU has seen 25-
50 ignition cycles without sensing any speed
input. Move vehicle at greater than 5 mph.
Did fault clear? Complete
Check adjustment on threaded
pencil speed sensor or drive tang
on mechanical speed sensor.
Sensor problem?
Switch off ignition.
Disconnect speed sensor and ECU from harness.
Check for shorts on ECU 30-way connector:
Round Connectors Rectangular Connector Pins
- K to Y - F2 to F3
- K to F - F2 to K2
- Y to F - F3 to K2
Was a short found?
Was circuit open?
Replace speed sensor.
Repair as
necessary.
Repair harness
as necessary.
Check continuity of speed sensor
input pin to ECU connector pins:
U (Round Connector)
F1 (Rectangular Connector)
Repair and verify
speed signal source.
Move vehicle at
greater than 5 mph.
Did active
fault clear?
Complete
Repair harness
as necessary.
No
Yes
No
No
Yes
Data Link
Yes
Analog
No
No
Yes
Check for opens:
Short speed sensor harness connector A
and B together.
Measure continuity between ECU connector
pins:
- K and Y (Round Connector)
- F2 and F3 (Rectangular Connector)
Switch off ignition.
Disconnect speed input from signal source
and ECU from harness
Check for short on ECU connector pins:
- U to F (Round Connector)
- F1 to K2 (Rectangular Connector)
Determine type of speed sensor input:
Digital (TTL signal from engine ECU or speedometer)
Analog (pole sensor or VR type)
Data Link (SAE J1708/1587 or SAE J1939)
Use industry standard tools to verify
data link signal is OK.
Digital
Sensor type?