KF - Testing Notes

NOTE: You should enter this Pinpoint Test only when you have been directed here from Quick Test or Diagnosis By Symptom.


REMEMBER


This pinpoint test is intended to diagnose only the following:

- Harness circuits: EDF, HEDF, EDF Power-To-Fan, HEDF Power-To-Fan, IGN Start/Run and GND.

- EDF Relay

- HEDF Relay

- Cooling Fan

- Processor assembly


DESCRIPTION

Electro Drive Fan/High Electro Drive Fan:

The EEC-IV processor determines engine cooling fan requirements and controls the fan operation through the EDF and HEDF outputs. The HEDF relay is a normally open relay. The EDF is normally closed.



BOTH FANS OFF


The HEDF output is off. The EDF output is on (grounded), which opens the normally closed relay.

EDF ON

The EDF output is turned Off, which closes the normally closed EDF relay. The HEDF output is off, and BATT(+) is supplied to the EDF relay through the HEDF relay.


HEDF ON

The HEDF output is on, which closes the HEDF relay. With the HEDF relay contacts closed, BATT(+) is not longer supplied to the EDF relay, Preventing both fan speeds from being activated at the same time.