Important: If the engine coolant heater does not heat the coolant, inspect all of the electrical connections before proceeding.

1. Disconnect the heater extension cord from the external 120 volt power supply before performing the following test.
2. Use a Digital Multimeter (DMM) to check for resistance.

Is the resistance equal to the specified value?

22ohms for 600 watt heaters

14ohms for 1000 watt heaters

Go to Step 2

Go to Step 3

1. Inspect the electrical power supply.

Any of the following conditions may cause the incorrect resistance:

•	A plug end

•	A faulty electrical extension cord

•	A blown circuit breaker

2. Inspect the electrical plug of the engine coolant heaters for corrosion and damage.
3. Clean the electrical plug as necessary.

Is the repair complete?

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System OK

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1. Disconnect the electrical plug from the engine coolant heater.
2. Measure the resistance at the heater.

Is the resistance equal to the specified value?

22ohms for 600 watt heaters

14ohms for 1000 watt heaters

Go to Step 4

Go to Step 5

1. Inspect the engine coolant heater terminals for corrosion.
2. Inspect the engine coolant heater electrical cord for the following conditions:

•

Damage

•	High resistance

•	If the cord exhibits high resistance, replace the cord.

Is the resistance equal to the specified value?

22ohms for 600 watt heaters

14ohms for 1000 watt heaters

System OK

Go to Step 5

Replace the engine coolant heater. Refer to Coolant Heater Replacement .

Is the repair complete?

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System OK

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