Hello Techs,

On a two fan system, Where are the relays? I'm interested in the purpose of the auxiliary fan relay. It seems my fan is not staying on for awhile after shutdown like it did in the past.

Thanks.

Mike

2000 Phoenix Red XKR

 

The fans are controlled by the Fan Control Module it is mounted on the fan assembly. When idling one fan is running, if the air conditioning is on the second fan will also be running. The second fan should always run when the A/C is on.
The main ffan gets its signals from the engnine temp sensor and the secondary gets its signal from the A/C controller.

 

The MY97-02 XK8-XKRs use a Series-Parallel Fan Control system. Both Fans run at the same time.

The ECM (Engine Control Module) receives various sensor signals (Engine Temp, AC on or off etc.)

The ECM requests the desired fan speed. The ECM has 2 control signal lines going to the Fan Control Relay Module. The Fan Control Relay Module contains 3 internal relays.

Possible Combinations of the 2 Signal Lines:

1) The ECM does not energize either control signal line = Both Fans Off.

2) The ECM energizes the Low Speed Signal Line Only = Both Fans connected in Series and each receives 6V. Both Fans are on and Quiet.

3) The ECM energizes the High Speed Signal Line Only = Both Fans are connected in Parallel and each receives 12V. Both fans are on and VERY LOUD.

 

Paul,
Can you explain the 2003 and up variable speed fan operation as well as you explained the two stage operation, Please.

 

The 03 and up ECM has a single control line to the Cooling Fan Control Module.

The signal is a PWM (Pulse Width Modulated) 140HZ Positive Duty Cycle, Range 7% to 95% to request a variable Fan Speed.

I don't know whether both fans are always on at the same time.

 

My fans on the '00 xkr are operating more like the first reply to my post. Where there is only one fan on and controlled by the engine temperature sensor and both are on when the A/C is on. I rarely hear the loud parallel function of unless of course I haven't been paying attention and have the stereo cranking in traffic.

'00 Phoenix Red XKR

 

This from the 2000 Electrical Diagram Set.

The Low Speed line goes directly to the ECM, Pin EM81-05
The High Speed line goes directly to the ECM, Pin EM81-04

The ECM receives Sensor Signals for Coolant Temp and other signals and then energizes either the Low Speed Request Line or the High Speed Request Line. These signals are in the form of grounding the Control Line.

The Low Speed Line activates the Upper of the 3 Relays through Pin LF9-9.
Following the diagram, this connects both fans in series resulting in 6V across each Fan.

The High Speed Line activates the Lower 2 of the 3 Relays through Pin LF9-7.
Following the diagram, This connects both fans in parallel resulting in 12V across each Fan.

There is NO direct connection from any Sensor to the Radiator Fan Control Module.

When the Fans are connected in series, it is possible for the fans to operate at different speeds due to differences in the resistances of the fan motors. IN fact, one of the Fans could be Jammed and the other Fan (in series) would still run.