Proheat X45–School Bus - Manual (Page 85)

PROHEAT INSTALLATION & SERVICE 5-28
Symptom: Coolant pump not running (code indicated)
Check: Coolant Pump wiring & function
a) That coolant pump is connected to harness correctly.
(See PROHEAT Wiring Diagram page 1-4)
b) The connector pins for damage or corrosion.
c) Harness for pinched or abraded wires.
d) Test pump. If it tests OK replace PCM.
(See Figure 5-24 and Test Procedure.)
Coolant Pump Mechanical & Electrical Troubleshooting (No code Indicated)
The following material covers the coolant pump mechanical or electrical problems
that do not indicate a Code 11. The coolant pump motor is ground side switched
— there is always voltage at the positive terminal to the motor.
Symptom: Coolant pump runs as soon as power is applied (No code indicated)
Check: Internal Short in Motor
a) Disconnect coolant pump motor from internal harness.
b) To check motor condition:
Spare Coolant Pump is Available – Check:
i) Connect spare coolant pump motor to internal harness
and apply power to heater.
If spare coolant pump does not run, replace the coolant
pump. If the spare coolant pump still runs:
ii) Inspect internal harness wires going to coolant pump.
Ensure that there is no chaffing or cuts that would provide
a coolant pump motor ground short.
If internal harness is in good condition, replace PCM.
Spare Coolant Pump is not Available – Check:
i) Plug connector that normally goes to coolant pump motor
into the blower.
If the blower does not spin when power is applied, this
indicates that there is a short in the coolant pump motor or
short in the internal harness. Verify root cause by checking
Steps (ii) and (iii).
If the blower spins, this indicates that there is a fault with
the PCM or there is a short in the internal harness. Verify
root cause by checking Step (iii).
ii) Measure resistance between either pin on the connector
going to the coolant pump motor and the body of the heater.
If the resistance is not in the mega-ohm range, replace the
coolant pump.
If the resistance is in the mega-ohm range, go to Step (iii).
iii) Inspect internal harness wires going to coolant pump.
Ensure that there is no chaffing or cuts that would provide
a motor ground short.
If internal harness is good condition, replace PCM.