Proheat M125 - Manual (Page 61)

COOLANT FLOW Diagnostic Code 3
Indicates that the coolant temperature in the PROHEAT reached 185°F (85°C)
within 90 seconds in Preheat mode or 60 seconds in Standard and Supplemental
modes from the beginning of Ignition. There is coolant in the system but its
flow rate is too low.
Troubleshoot the Coolant Flow diagnostic code based on:
1. Vehicle coolant system. Go to Step 1.
• The PROHEAT starts and runs for 90 seconds in Preheat mode or 60
seconds in Standard and Supplemental modes or less and shuts
down with a Coolant Flow diagnostic code indicated.
2. Coolant Pump system electrical or mechanical fault. Go to Step 2.
• The PROHEAT starts and runs for 90 seconds in Preheat mode or 60
seconds in Standard and Supplemental modes or less and shuts
down with a Coolant Flow diagnostic code indicated.
Vehicle coolant system – Check:
a) For restrictions and blockages in the coolant lines.
b) OEM system shut-off valves for correct operation.
c) For loose hose clamps – air introduced into the system.
d) Coolant line size, fittings. Are they too restrictive?
e) Direction of flow. Are the PROHEAT Coolant Pump and the engine Coolant
Pump pumping in the same direction when they are operating at the
same time?
f) Coolant capacity. Is there enough coolant in the system? Go to Technical
Specifications, page 1-1.
g) PROHEAT location. Is the PROHEAT or Coolant Pump the high point in the
system? Coolant Pumps are not self-priming and a surge tank may
be required.
Coolant Pump and G-II PCM – Check:
a) G-II PCM electrical function.
b) Coolant Pump electrical function.
c) Coolant Pump mechanical function.
Test Procedure – Electrical:
a) Disconnect the Coolant Pump connector at the G-II PCM.
b) Using a multimeter set for voltage, switch the PROHEAT on and measure
across pins A and B on the G-II PCM Coolant Pump connection.
If the correct nominal system voltage (12 or 24) is measured, the G-II PCM
is OK. Go to Procedure – Mechanical inspection and testing, page 4-25.
If no voltage is measured, the G-II PCM is faulty. Go to G-II PCM
replacement, page 4-38.
COOLANT FLOW: Step 2
(3 Flashes)
COOLANT FLOW: Step 1
(3 Flashes)
WARNING
NEVER remove coolant lines when
the engine is hot – escaping steam
or scalding water could cause
serious personal injury. Loosen the
coolant line clamps slowly,
allowing the pressure to escape
before removing completely.
4.1.4
(3 flashes)
4-24 PROHEAT M-SERIES G-II PCM SERVICE MANUAL