Fault Code Guide

Fire Pump Controls Function Electrical Diagnosis
Test
No.
Test Procedure Test Result Action
3 Make sure the vehicle has full air pressure. Turn the ignition
on.
Using the appropriate solenoids Datalink Monitor template,
attempt to engage the fire pump using the smart switch in the
dash while observing the status of the pressure switch under
the "Inputs to BHM" heading for the two solenoids that control
the fire pump. See Fig. 2 and Fig. 3.
NOTE: Under normal operation with the switch off, one
solenoid should indicate air pressure, the other one should
not. When the switch is turned on and the pump engages, the
solenoid that indicated pressure should now be off, and the
one that was off should now indicate pressure.
Does the status of the pressure switch change for both
solenoids when the switch is turned on, even if it reverts back
to its initial state?
Yes
Go to test no. 4.
No
For the solenoid that does not
change pressure switch status:
• Check solenoid pressure
switch feedback circuit.
• Check the solenoid pressure
switch. See Section 42.19.
• Check the air lines.
If the above items are OK, replace
CHM.
4 In ServiceLink, open the "Fire Pump Interlocks" Datalink Moni-
tor template.
Using Table 5, determine which fire pump interlocks are used
based on the reference parameter programmed into the BHM.
Engage the fire pump using the switch in the dash.
Do any of the necessary interlocks drop out when the fire
pump solenoids drop out?
Yes
Determine the cause for interlock
drop out and repair as necessary.
No
Check both fire pump solenoid out-
put circuits for amperage. If either
exceeds 0.85A, make necessary
repair or modification.
If amperage is OK, check for me-
chanical problem.
PTO and Pump Electrical Controls 54.38
Troubleshooting
Business Class M2 Workshop Manual, Supplement 22, September 2012300/4