2005 Boxster S cooling fan will not turn off

[Bruizerman]

2005 Boxster S driver's side cooling fan will not turn off.
Retired General Motors electrician with background in electronics.
Working on a friend's Boxster.
Searched threads here but couldn't find an answer.
Had to disconnect battery to stop fan. After tracing wire back, found fuse block under hood on passenger side fender wall; pulled supply wire (12 GA red) to kill fan #2. It originates from firewall bundle so I assume it goes to relay bank.
Pulled all relays (driver's side foot well, trunk relay carrier) but still hot.
We know FAN #1 is a different animal with it's own control unit.
Does the DME control it?

What are we missing?

Thank you.

[tcora]

Not specifically familiar with the 05, but on my 03, both are DME controlled (high and low speed) and fed from a relay on the fuse panel in the driver’s side footwell. There are also individual fuses for each fan, IIRC.

[JFP in PA]

The 05 car is most likely a PWM (pulse width modulated) controlled fan system that lacks the resistors of the earlier cars.

[tcora]

Originally Posted by JFP in PA

The 05 car is most likely a PWM (pulse width modulated) controlled fan system that lacks the resistors of the earlier cars.

Still presumably controlled by the ECU?

[JFP in PA]

Yes, the major difference is that the fan control module controls the fan speed by varying the power pulse width going to the fan motor. Lighter, fewer components, more dependable than multiple resistor circuits; and the fan speeds can also be infinitely varirable rather than fixed. The fan motor for the cabin heater also went this way for the same reasons.

[JFP in PA]

The larger headache with PWM is diagnostics as you need devices that can read and record the pulse width, as well as a pulse generator to supply known power to see if the driven device works.

[tcora]

Originally Posted by JFP in PA

The larger headache with PWM is diagnostics as you need devices that can read and record the pulse width, as well as a pulse generator to supply known power to see if the driven device works.

Yup. Oscilloscope or spectrum analyzer is your friend.

[Bruizerman]

Discovered that the Fan Control Module in the R wheel well also powers FAN #2 in the L wheel well.

The wire goes back through the wheel well, along the fender, into the dash, back through the firewall all the way to the L wheel well and powers FAN #2. Wow.
Ordered a new module.

[CarGuyNeil]

Thanks for sharing. That's helpful for someone...

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