Fault Code Guide

Fire Pump Controls Function Electrical Diagnosis
Test
No.
Test Procedure Test Result Action
1 In ServiceLink, use the Chassis Module (CHM) Configuration
screen to determine which CHM solenoid output numbers
control the two solenoids for the fire pump.
Then open the "AMU Solenoids Circuits" or "AAVA Solenoids
Circuits" in the appropriate Datalink Monitor template.
Make sure the vehicle has full air pressure. Turn the ignition
on.
Attempt to engage the pump using the smart switch in the
dash while observing the status of solenoid output under the
"Outputs from BHM" heading for both of the solenoid numbers
determined above. See Fig. 1 and Fig. 3.
Does the status of the solenoid output for both solenoids turn
on at all? They may turn on, then drop out.
Yes
Go to test no. 2.
No
Perform the PTO and Fire Pump
Control Switch and Interlocks Test
in Table 3.
2 Using the appropriate solenoids Datalink Monitor template,
enter Test Mode.
Attempt to turn the fire pump control solenoids on one at a
time using the ON buttons on the template.
NOTE: When done, exit Test Mode.
NOTE: If operating normally, one solenoid should exhaust air
when turned on, the other will exhaust air when turned off.
What happens when the solenoids are turned on?
Both operate Go to test no. 3.
Neither operate Go to test no. 5.
Only one
operates
Make sure one of the reference
parameters in Table 5 is applied to
the vehicle. If not, correct as
necessary.
For the solenoid that is not
working, make sure it is wired to
the correct CHM output pins per
the ServiceLink CHM Configuration
screen.
Check the solenoid output circuit
from the CHM to the solenoid,
including the solenoid coil ground
circuit, for opens.
Check the solenoid output circuit
between the CHM and solenoid for
short to ground. This will cause the
CHM solenoid output to shut off
due to high current. The current
draw must not exceed 0.85A.
Check the solenoid. See
Section 42.19.
If all of the above is OK, replace
the CHM.
PTO and Pump Electrical Controls 54.38
Troubleshooting
Business Class M2 Workshop Manual, Supplement 22, September 2012 300/3