MI91.327A
01NOV11
725 TROUBLE SHOOTING STEPS
MANUAL OPERATION
NOTE: The following diagnostic functions are written in order of operation and should be checked in this order.
Failure to do so may cause improper diagnoses of the problem(s) and increase the time needed to repair the system.
PART 1. TOUCH PANEL TO I/O MODULE COMMUNICATION CHECK.
A. Neither link light is on,
SEE: MP84.3170 and MP84.3334
IMPORTANT: Due to painting techniques of chassis rails or components and the construction of the chassis’s, it is
possible to have grounding issues between frame rails. When voltage issues are addressed, it is important to check
chassis grounds, positive voltage connections and battery condition to ensure a good DC voltage circuit for the
vehicle. Problems with these items, especially the chassis grounds, will create voltage issues for the HWH
equipment.
Note: Only review this section as an educational aid or if directed to PART 1 from other diagnostic steps in this
manual.
There should be communication between the touch panel and the I/O module anytime the ignition is in the ON or
ACC. position. The touch panel and the I/O module each have a "Link Light". If both link lights are flashing, this
indicates proper communication between the touch panel and I/O module. If either link light is off or on but not
flashing, there is a communication problem. The link lights will flash with the park brake on or off but the ignition
must be in the ON or ACC position.
CAN Information: Communication between the touch panel and I/O module is provided by a twisted pair of yellow and green
check the "TRAVEL MODE" light on the touch panel. If the
"TRAVEL MODE" light is off, there may be no power to the touch panel or I/O module,
B. If the "TRAVEL MODE" light is on or one link light is on or flashing, turn the ignition
off. There must be no power to the I/O module for the following tests. Make sure the yellow
connector. If there is proper resistance of 60 ohms (±10%)
and green wires are properly seated into the 32 pin and 5 pin connectors. If the wires and
or the touch panel. There is no good test to determine which is bad. The touch panel would
SEE: MP84.3334
Note:
If the ohm meter shows improper resistance,
unplug the touch panel and check pins 1
SEE: MP84.3170
and 2 of the harness connector. If the resistance is now ok, replace the touch panel. If the
resistance is still incorrect, plug the touch panel back in and unplug the 32 pin I/O module
connector. Check between pins A2 and B2 of the 32 pin harness connector. If the resistance
is good, replace the I/O module. If the resistance is incorrect, there is a problem with the yellow
wires. At each end of the harness there is a 120 ohm resistor connecting the two wires. These are called terminating resistors.
The yellow wire is in pin A2 of the 32 pin I/O module connector and pin 1 of the 5 pin MTA touch panel connector . The green
wire is in pin B2 of the 32 pin I/O module connector and pin 2 of the 5 pin MTA touch panel connector. When using an ohm meter
to check the yellow and green communication wires, the meter should show 60 ohms, ±10 % when checking between the two wires.
check resistance between pins 1 and 2 at the 5 pin touch panel
PUMP RELAY
MASTER RELAY
LINK LIGHT
1
8
6
7
5 4
3 2
D
C
B
A
TRAVEL
DUMP
MP84.3170
PIN 1
LINK LIGHT
PIN 1
PIN 4
MP84.3334
pins are properly seated,
the problem is the I/O module
Although the resistance between the green and yellow wire is good, it may be possible
that a wire may be shorted to another wire in the harness that affects communication but not
the resistance of the terminating resistors. If the resistance shown with the touch panel and
I/O module plugged in is ok, unplug both and check for continuity between the yellow then
green wires and the other wires in the 32 pin connector. There should be no continuity.
go to PART 4, section B of the trouble shooting steps.
be the easiest to try first.
and green communication wires.
MP84.3170
LINK LIGHT
MASTER RELAY
PUMP RELAY
5
7 6
8
A
B
C
D
2
3
4
1
DUMP
TRAVEL
