PWM fans with P59 ecu or "EV Fan Type" setting

[bobcratchet555]

it appears that a lot (or all?) of the P59 OS's have an option for "EV Fan" which i guess really means electro viscous fan clutch. There are also tables for PWM output vs coolant temp which of course do not get used for the traditional relay controlled e fans.

it appears as if this was used on the trailblazers/trailblazer family (envoy, rainier, etc). if you look at the water pumps for these vehicles on rock auto you can clearly see an electrical connector on the fan clutch.

has anyone done any experimenting to see if the PWM output from this could perhaps be suitable for driving PWM e fans?

if no one has proven it cant be done i am going to start looking for an ECM from one of these vehicles and see what the output looks like.

[bobcratchet555]

there is a 2004 envoy tune in the 2004 bin files thread. If you look at it the fan type is set to 3 (EVFans).

[Fast355]

I have the EV clutch now run by PWM with the RPM feedback on my 97 383 van. It is unlikely the code will run PWM electrics correctly. The PWM code is looking is looking for a fan RPM input signal in addition to supplying the clutch with the PWM signal. As a clutch fan control it works great.

[bobcratchet555]

I have the EV clutch now run by PWM with the RPM feedback on my 97 383 van. It is unlikely the code will run PWM electrics correctly. The PWM code is looking is looking for a fan RPM input signal in addition to supplying the clutch with the PWM signal. As a clutch fan control it works great.

question is tho what frequency is the PWM output, and can you use one of the tables to essentially disable the feedback loop? specifically the "PWM output driver delta" which is present at least in the 05 operating system with the XDF i am using. In theory if you zero out this table and turn off the fan diagnostics, would it just use the duty cycles from the "Fan PWM %"?

[Pulse_GTO]

I went ahead and define all the Fan tables for the 7603, can be found under Vehicle Settings>Fans in the attached XDF. Hopefully this helps.

[bobcratchet555]

I went ahead and define all the Fan tables for the 7603, can be found under Vehicle Settings>Fans in the attached XDF. Hopefully this helps.

thank you, much appreciated. At this point i really just need to grab one of these PCMs from the yard and measure the output with a scope. If the frequency is in the range that could work with pwm fans i'll at least give this a try.

[???]

just thought I'd add real quick that it might be useful to pick up the pwm box from I believe it's a Ford something. it's the same box the c6 corvettes use but at cheap price and in junk yards. that will allow you to test out if pwm works using a brushed fan. before buying a brushless setup.

if it runs the box, it will runs a gm oem brushless. I switched my c6 from the box and stock fan to a brushless c7 fan and it was plug and play.

also even in the Gen 4 ecm pwm output is just the relay control being pulsed real fast. the tables doesn't really work like you'd think. it's more like using the relay settings of off low and high point and blending them together to make a curve. so I think this is possible to work.

[bobcratchet555]

just thought I'd add real quick that it might be useful to pick up the pwm box from I believe it's a Ford something. it's the same box the c6 corvettes use but at cheap price and in junk yards. that will allow you to test out if pwm works using a brushed fan. before buying a brushless setup.

if it runs the box, it will runs a gm oem brushless. I switched my c6 from the box and stock fan to a brushless c7 fan and it was plug and play.

also even in the Gen 4 ecm pwm output is just the relay control being pulsed real fast. the tables doesn't really work like you'd think. it's more like using the relay settings of off low and high point and blending them together to make a curve. so I think this is possible to work.

thanks, i greatly appreciate the input!!