The Ram gauge issues seemed to have gone away for a while. I wasn’t at all sure I had fixed them, but they nearly disappeared — until this week, when things started going nuts again. AC cutting out, and this time, since I was driving in the rain, I discovered that the wipers stopped working as well.
The whole time, the ECM has had a P0483 code stored, which indicates a problem with the fan speed (either below 50 RPM or above 6000 RPM, but it can also mean that the fan clutch just isn’t behaving in a way the ECM expects it to).
I finally bit the bullet and started going through the fan clutch testing procedure. I got to the point where I needed to start unplugging ECM connectors and stopped, because to do that I’ll need to remove the driver’s side splash guard again, and that takes a little time.
But I thought I had assured myself that the fan clutch was not bad, because it passed tests 1 through 4, meaning the clutch itself has no internal shorts.
However, I did some research into how this “electro-viscous” fan clutch works. It is basically very similar to a purely mechanical viscous clutch, in the sense that it has a coil that tightens with temperature, engaging a valve that allows viscous silicone to pour into parts of the clutch, engaging the shaft that connects it to the water pump and making the fan turn faster and with more force the hotter the engine gets. But an electro-viscous clutch has a few extra features: an RPM sensor that feeds back to the ECM to tell it how fast the fan is actually turning (which it can then compare to the engine RPM), a command wire, and a +5v supply to a heating element inside the clutch. This allows the ECM to turn on a heating element, which will very quickly cause the silicone to pool in the clutch and fully engage the fan. Obviously, one reason for the ECM to command this is if the engine is getting too hot, but another reason it will do so is if the air conditioning is turned on at idle speed. This will ensure adequate airflow over the condenser coils, with the added benefit of ensuring the engine stays cool too.
The important takeaway for me was that the clutch will function just fine to keep the engine cool even if the electric part is disconnected. You simply lose the ability for the ECM to tell the clutch what to do, as well as sensing what it is doing. Now, with that P0483 code stored, I don’t believe the fan clutch is working properly anyway.
So I decided to disconnect the clutch and drive the Ram to work this morning and see what, if anything, happened as a result. I’ve seen in several places online that when you get the P0483 and P2509 codes together, that’s a strong indication of a bad or going-bad fan clutch. Apparently, when one of these clutches goes bad, the failure (usually a short) brings down the bus. However, since I cleaned a bunch of grounds, the battery terminals, the ECM connectors, and the two connectors across the bellhousing, the P2509 code has gone away — but the P0483 code has remained the whole time.
Well, after driving to work this morning, nothing unusual happened. The truck didn’t overheat (not that I expected it to), but also there was no gauge weirdness at all, either. Now, that’s inconclusive; the gauge weirdness is so random that you never know when it will happen. But it’s a somewhat positive sign.
At lunch, I decided to do a test of whether turning the AC on at idle actually engages the fan clutch. I ran the truck with the clutch disconnected to spin any silicone out of the clutch, then shut it off and hooked the clutch up. Started it back up and turned on the AC and waited about a minute (the spec says the fan should fully engage within 45 seconds). But upon increasing idle to nearly 2000 RPM, it became apparent that the fan was not engaged. I couldn’t hear it over the engine at all.
So it seems likely that, somehow, the fan clutch is not working properly, but I don’t know what the malfunction is.
I am going to leave it disconnected and drive the truck for a while. The gauges misbehave most severely in the afternoons when it’s hot and I’m running the AC. If I don’t see any gauge malfunctions, I think it’s really likely the fan clutch is the cause of these electrical issues and should be replaced.