Fan clutch / MAP sensor questions

[AH64ID]

I agree.

Or anything with the fan. It's not the system I would be trouble shooting.

 

[Tuesdak]

I was able to monitor the PWM. It was at "0". When should I see it change? I had the truck running and in park and was giving it RPM's and it just stayed at "0".

The fan is not locked in to a full RPM. It does vary. Say I'm doing 40 MPH, I can watch the fan RPM drop from say 1500 down to 1300 and quickly go back up again. Driving around town is where the fan is say 300-500 RPM lower than engine RPM.

Once I go on the highway it will be at 1050-1160 RPM and the engine is turning 2100 RPM. Once I get off highway, it seems to be ok staying around 1200 RPM. If I turn the truck off and on again, the craziness starts all over again.

And PWM was at "0" the entire time? This is literally the number you care about to see if the ECM is calling for fan at all for any reason. I would unplug the fan connector and at 1200+ engine RPM see if it kicks out. (Idle is slow to change fan RPM.) Again 15% PWM is "maintain fan RPM" and Zero, 0, PWM is "SLOW DOWN". Plug it in (engine off of course) after say 5 min of 1200+ engine RPM and immediately see what the fan RPM is at idle. Unless you have a handheld optical tach and can measure the FAN RPM yourself. I recall 300-600 RPM kicked out at idle on a shot clutch and a new clutch was higher RPM. I don't recall exactly but IMO 1200 FAN RPM or less is kicked out. The AC needed ~1500 FAN RPM at idle to work on my 2003.

The OEM troubleshooting for the EV fans is a damn joke. This includes GM. It's more of avoiding warranty claims.

It's down to three things:
1) PWM is 15% or more - ECM is calling for fan so troubleshooting sensors other things rather than the fan system.
2) Short in wiring bringing on the fan by supplying 12v to it. This would likely cause full RPM from the fan, but, not all shorts are dead shorts.
3) Failure in fan clutch allowing it to kick itself on. Debris holding electronic valve open, bearing locking up, whatever. GM had all kinds of trouble with things internally failing in their EV fan clutches on Trailblazers.

4) Bad ECM goes hand in hand with the intermittent short. You would need to backprobe the fan connector and see if it's getting +12v signals. From the truly weird failure where fiction has to be plausible the truth does not. Unplugging fan as suggested above would clear this suggestion up without backprobing.

 

[AH64ID]

I have never found the PWM indication of the fan to be all that accurate. I think it fluctuates faster than the OBDII can often report, which is why I've seen fan RPMs increase with 0% PWM.

 

[Tuesdak]

Then the unplug the fan connector would be the acid test. The 2003 ECM I studied was an oddball vs. the newer ones so absolutely it could be different in reporting PWM.

 

[Oil Stain]

Thanks everyone for more help!
Ok I did what Tuesdak said, I revved the rpm to 1200 and disconnected the fan plug. The speed of the fan did not change. I did this a couple of times with the same result.

Below is a screen shot of the Alfaobd app. The flat line is me at highway speed, then getting off highway and got stopped at a traffic light. The flat low rpm. Then headed back to campground and seeing high rpms. What your seeing isn't bad at this point because I hit the highway. If I'm never able to get to highway speed she closely matches engine speed.

Once I get on the highway the fan drops to around 1100 rpm. If I stay driving around town never going over 50mph, the fan closely matches rpm and will fluctuate trying to go lower then going right up close to engine rpm. I could then hit the highway and have to have engine rpm at a steady 2k+ before it will settled down.

 

[Tuesdak]

So with the fan plug "disconnected" did the crazy fan RPM/noise "go away"? It's rough to follow a fan with windmilling at road speed and changing engine RPM.

 

[Oil Stain]

So with the fan plug "disconnected" did the crazy fan RPM/noise "go away"? It's rough to follow a fan with windmilling at road speed and changing engine RPM.

I'm sorry I miss understood, I unplugged it on high idle and did not drive it that way. I will do that then. I will be able to here the fan if its spinning fast or not.

 

[Tuesdak]

I'm sorry I miss understood, I unplugged it on high idle and did not drive it that way. I will do that then. I will be able to here the fan if its spinning fast or not.

Me too.

 

[sag2]

Take a couple towels and completely cover the front end. Run it with AC off at high idle and see if you can get the coolant temp up to about 215-220. You should hear the fan start to roar as the fan kicks in. If it does, pull the towels and the coolant temp should drop quickly and the fan will start to disengage as it gets near 210-205..

 

[Oil Stain]

So with the fan plug "disconnected" did the crazy fan RPM/noise "go away"? It's rough to follow a fan with windmilling at road speed and changing engine RPM.

Ok, here's what I got. I unplugged the fan connector and drove into town. The fan was much quieter especially at higher rpm's. The fan sounded about the same up to about maybe 1200-1300rpm. Above that was quiet. Doing a remote start the fan was turning and could feel the air coming through the seams of the hood like I always have had.

I tested the connector for 12v on pin 6. The truck was started for the first time cold. I was reading anywhere from 12.4-13.6v. Was going back and forth. After about 30 seconds the voltage dropped to 3.3-3.6v and stayed there no matter what rpm I gave it.

I found a troubleshooting paper from Mopar, but from what I'm reading, it's troubleshooting for a fan that WON'T engage. It says that you should supply 12v to fan connector and the fan should match the rpm's up to 2000rpm's.

I have the opposite issue except when driving on the highway then fan run around 1100rpm.

I have attached the document.

 

[Oil Stain]

Take a couple towels and completely cover the front end. Run it with AC off at high idle and see if you can get the coolant temp up to about 215-220. You should hear the fan start to roar as the fan kicks in. If it does, pull the towels and the coolant temp should drop quickly and the fan will start to disengage as it gets near 210-205..

sag2, thanks for posting. I will try that as soon as I am able. Thanks again.

 

[Oil Stain]

Tried the towels. ECT would not go over 201F reading on digital gauge.

 

[Ozymandias]

Ok, here's what I got. I unplugged the fan connector and drove into town. The fan was much quieter especially at higher rpm's. The fan sounded about the same up to about maybe 1200-1300rpm. Above that was quiet. Doing a remote start the fan was turning and could feel the air coming through the seams of the hood like I always have had.

I tested the connector for 12v on pin 6. The truck was started for the first time cold. I was reading anywhere from 12.4-13.6v. Was going back and forth. After about 30 seconds the voltage dropped to 3.3-3.6v and stayed there no matter what rpm I gave it.

I found a troubleshooting paper from Mopar, but from what I'm reading, it's troubleshooting for a fan that WON'T engage. It says that you should supply 12v to fan connector and the fan should match the rpm's up to 2000rpm's.

I have the opposite issue except when driving on the highway then fan run around 1100rpm.

I have attached the document.

If you can hear a disconnect Fan then either your hearing is waaay better then everyone's else or your fan blade is compromised in someway.

It is just not normal to hear that fan over the diesels noise just driving around tow.
I've a hard time to hear mine even if it is 75% engaging up the hill - and my hearing is excellent too.

 

[Ozymandias]

Oh, and the fan is always turning just by the drag of the coupler. It never stands still as long as the engine is running. There is no OFF on a vistronic-fan compared to an electric fan.

 

[Oil Stain]

If you can hear a disconnect Fan then either your hearing is waaay better then everyone's else or your fan blade is compromised in someway.

It is just not normal to hear that fan over the diesels noise just driving around tow.
I've a hard time to hear mine even if it is 75% engaging up the hill - and my hearing is excellent too.

Not sure what to say to that LOL. I've been having this issue for a while, so I know the sound. I'm good with squeaks and rattles too. Fixed many in my years. My truck is very quiet inside and the diesel isn't that bad compared to others.

 

[Oil Stain]

Oh, and the fan is always turning just by the drag of the coupler. It never stands still as long as the engine is running. There is no OFF on a vistronic-fan compared to an electric fan.

Yeah I know...
What is the advantage over the electric design. I would think you would have better control on the electric fan and less issues. My guess would be electric power consumption when engine starts to over heat, if I had to hazard a guess.

 

[Ozymandias]

Yeah I know...
What is the advantage over the electric design. I would think you would have better control on the electric fan and less issues. My guess would be electric power consumption when engine starts to over heat, if I had to hazard a guess.

Yes, at some size of engine the electric solution is just to weak, it would need a 15kw Fan motor to replace the Power of the Vistronic Fan.
Every big engine has a colling fan that is either direct drive with a belt or hydraulic.

 

[Tuesdak]

Looks like the fan clutch isn’t the problem.

Need to run the flow chart on the sensor reading funny. I would guess a connection has high resistance causing a higher reading then it really is. Corrosion, oil in a connector, etc. There a wire diagram available?

 

[Oil Stain]

Yes, at some size of engine the electric solution is just to weak, it would need a 15kw Fan motor to replace the Power of the Vistronic Fan.
Every big engine has a colling fan that is either direct drive with a belt or hydraulic.

I had a feeling that might be it. Thanks.

 

[Oil Stain]

Looks like the fan clutch isn’t the problem.

Need to run the flow chart on the sensor reading funny. I would guess a connection has high resistance causing a higher reading then it really is. Corrosion, oil in a connector, etc. There a wire diagram available?

What sensor? Fan, MAP?