LSR

This post is related to another of mine started on April 9 regarding a problem with my 2013 991.1 Carrera S that causes the front radiator fans sometimes (but not always) to turn on full blast after the engine's been shut down. I'm starting a new thread because the techs at my dealer's shop are stumped. They have witnessed the fans misbehaving, but after 5 days with the car in the shop cannot figure out the cause. The car is throwing no fault codes, yet the problem persists. I'm hoping someone out there may have a clue about what might be to blame. For my previous post, see here: https://rennlist.com/forums/991/1189108-strange-front-radiator-fan-problem.html.

I'm going to be as succinct as I can in describing the problem and all its symptoms.

The problem: both front radiator fans inexplicably turn on full blast some minutes after the engine's been shut down. The last time this happened, the fans apparently turned on (unbeknownst to me) after I had parked the car in the garage and retired for the evening. The the next morning, the battery was dead. I replaced it, thinking the battery was on its way out anyway and the root cause of the problem. However, the fans continued to misbehave, Here are the scenarios of when the fans turn on, and when they don't. Somewhere in here, there must be a clue as to the root cause:

1. Engine warm but not hot: the fans turn on some number of minutes after shutdown if the car has been driven lightly and the engine is warm but has not reached full operating temperature. The fans stop when a driver's door is opened or the car is locked or unlocked, but then they will start up again a minute or so later. Sometimes it is impossible to get the fans to stop and stay stopped unless the car is driven to get the engine to full operating temperature.
2. Engine at full operating temperature: the fans behave normally and do not turn on after the car's engine is shut down if the car's been driven enough so that the engine is at full operating temperature.
3. Engine cold and new battery connected: when I replaced the battery, even though the car had been sitting idle for a few days, as soon as I connected the new battery the radiator fans started to run. They turned off and stayed off after I opened the driver's door.

The question is, what can be causing this aberrant fan behavior? I initially thought it was my car's 6-year old battery that caused the problem. There are dozens of reports on the forum of dying batteries causing all sorts of mischief with a 911's systems. But even after replacing the battery with a Porsche battery purchased from my dealer, the problem surfaced immediately upon the new battery being connected and continued to manifest as outlined in 1-2, above.

Luckily for me (so I thought at the time), the fans acted up in the shop when I dropped off the car. My dealer is only a few miles from my house, and driving the car there got the engine warm but not to full operating temperature, And sure enough, the fans started a few minutes after I had dropped off the car and left. So the tech (and my SA) both witnessed the problem first-hand, and even managed to reproduce it after a short test drive. And that's the end of the good news.

After 4 full days in the shop, I was told today that the car's systems have no fault codes. Last Friday, after a test drive, the tech noticed that the car's charging system voltage was low - around 12.2 volts - and that led him and the shop foreman to believe the fault lay with the alternator. Today, they tested the charging system again in 3 situations - (1) with the engine cold, (2) with the engine warm, and (3) with the engine at full operating temperature. But this time, the charging system and the fans behaved and performed flawlessly. So the tech and the shop foreman are no longer sure what the problem is. They still believe it's the alternator - they said they are "80% sure" - and I was told the cost to replace it would be an eye-watering $1,964. I decided to pass on that right now, as I'm not willing to place a $2K bet on a "fix" that has a 1-in-5 chance of not working.

If you were to look at the wiring diagram for the car, you'd see that there are not many possible direct causal candidates for the problem. The culprit is pretty clearly not a fan relay, because there are two - one for each fan - and each fan is individually controlled by PWM (pulse-width modulated) signals from the DME. That both fans are turning on and off simultaneously pretty much rules out the individually operated fan relays as faulty. Next thought is it could be the DME unit itself, but again there are no fault codes and the dealer is not suspecting it. Upstream from and connected to the DME there are two temperature sensors. One sensor is the Engine Coolant Temperature Sensor (on DME pins 43 & 42) and the other is the Engine Compartment Temperature Sensor (on DME pins 40 & 42). The problem is not likely caused by the Engine Compartment Temperature Sensor because the engine compartment purge fans operate normally (they might run-on after shutdown as they should only if the engine bay is hot and they then shut off and stay off). That leaves only the Engine Coolant Temperature Sensor as a possible direct cause. But when I asked the shop foreman about, he said quite definitively that's not the problem.

So, that's it. If I take Door No. 1 for $2K, I'll replace the alternator with no confidence the problem will be fixed. If I take Door No. 2 and don't replace the alternator, I'll get the car back with the problem unresolved and no further understanding of what the cause might be. I have asked my dealer to reach out to PCNA dealer tech support, thinking the geniuses in Atlanta have seen it all and may have a better idea what's causing this. I hope to find out tomorrow what they say. But I'm not very confident the dealer and PCNA will even connect. And so, at wit's end, I'm reaching out to the online community for help. BTW, in case you were wondering, the act of opening the driver's door or locking/unlocking the car as causing the fans to shut down is, I'm told by my dealer, completely normal. I was told that when the driver's door is opened or the car is unlocked, the car assumes you're going to start it and so the DME shuts down all extraneous electrical systems to provide maximum power to the fuel pump and starter. When the car is locked, the car puts the electrical systems to sleep and this, too, would typically shut down the radiator fans.

Thanks in advance for any insightful and thoughtful help anyone can provide.

_RS_

"charging system voltage was low - around 12.2 volts"
Do you see that on the voltage gauge? It's seriously low. Put a charger on the battery to fully charge it and the voltage should not drop too much with your "test" run which reproduces the issue. If the alternator is knackered it won't matter until the battery gets low again.

(I've replaced a battery and one of the things that was happening was the engine fans coming on for a few minutes when I closed a door or the frunk, that has gone away)

Jack F

Can one of the fan relays be on it’s way out giving back faulty info causing the system to run both fans? How much are fan relays? Is everyone sure that it cannot be both?

LSR

Thanks for your post. I appreciate it. Unfortunately, the car's circuit diagram shows the fan relays are actuated individually by the DME and, because of this, it is highly unlikely for the relays to be the source of the problem which manifests as both fans turning on and off in unison. If one relay was on its way out, only one fan should misbehave, not both.

_RS_

So frustrating for LSR that we still live in an age of poke-and-hope with cars, I don't think we should pay for that if the dealer cannot diagnose, perhaps they should do it for part cost and charge labor if it fixes it?
This reproducible event in the ECU/DME should be able to be trapped and traced back to the cause.

Good luck, LSR.

LSR

Thank you for your post. Your battery replacement experience and aberrant fan operation before you replaced the battery seems to confirm what both I and my shop have been thinking, namely that the immediate cause of the fan actuation is a drooping battery voltage. If it is a voltage-related issue, though, what's causing that? The battery is brand new, so that's not to blame. If the alternator caused Friday's low voltage readings, then why was it and the charge system operating perfectly today? And why are there no faults codes? This is what's got my shop stumped. They think it's the alternator, but can't nail it down to that. If I knew that someone else out there had a similarly weird problem that was demonstrably caused by a wonky alternator and resolved by a new one, I might feel more inclined to place a $2K bet on replacing it.

Bud Taylor

So I can sleep at night please dont pay 2k dollars to a stealership for an alternator. At a qualified indy this is a $500 job and if you have a buddy its a $300 job. That price is obscene.

paddlefoot64

Going out on a limb here, but is voltage regulator to blame for erratic charging and possible parasitic drain?

LSR

I assumed the dealer's price would be on the high side, but didn't realize how much higher. Please sleep at night! If I get the work done, it won't be for $2K.

polobai

If you are a DIY person, the alternator may not be too hard to do. Worth a shot-I have seen alternators have intermittent failures and eventually fail completely over time. My guess is that yours is on the way out judging by the 12.2 voltage reading when the car was running. Most times what I do is have the OEM alternator rebuilt at a local alternator/starter rebuild shop. This way its still an OEM part on the outside and there is no chance of fitment issues (considerably cheaper as well). Honestly, most alternators you buy are rebuilt anyway-may as well save the cost on the front end.

LSR

Good question, but I don't know the answer. I don't even know if there is a voltage regulator in the car. You'd think there should be, but neither the parts list nor the service manual make mention of one. Looking at the wiring diagram for the charging system, there's something called a "battery sensor" that's connected to the alternator. And the repair manual mentions the battery sensor and says a new battery sensor installed in the car is detected and documented automatically by the gateway control unit. But what the battery sensor does, and whether or not it might be a play here, I have no idea. Interestingly, the dealer's shop has never mentioned the battery sensor as a suspect.

LSR

Thanks. I can DIY many things, but not this one. Without a shop manual for the car, a PIWIS tester, a bunch more tools than I own, and some experience inside the car's engine bay, changing out the alternator is not something I'm keen to try (at least on my own car ).

digits

Wait a second - it's only 12.2v while the car is running? That does make the alternator a likely suspect. Even with your new battery I bet the voltage is really, really low when the car is turned off and all sorts of weird behavior is possible from what I've seen in numerous "old battery" threads.

ClassJ

One story that could help. (although different make and model). Are they suspecting the alternator is outputting AC? Otherwise I would think temperature sensor more than anything.

On my 2006 Mustang GT. A few years ago it threw a code for a camshaft timing sensor and the car had a repeated bucking/hesitation issue coupled with the CEL. Thankfully I googled the issue prior to ordering a new cam sensor and pulling the timing cover off.

Turns out, on that car, the alternator diode/rectifier assembly typically fails and injects excess AC/ripple into the system. This, in turn, can cause all sorts of wacky behavior. This is not something that Ford includes in the shop manual or fault tree. The charging system was working fine.

In that case, the instructions from the forum posts stated to check the AC voltage at the battery. If it was more than X, that indicated a bad alternator rectifier. It did. I changed the alternator, cleared the codes, and the issue was fixed.

LSR

I don't know the particulars on when the shop saw the low voltage - engine running or not. But that was last Friday, and yesterday when they were digging into the charging system and testing the heck out of it at various engine temperatures everything and all voltages checked out fine. I've never heard of an alternator going bad and then not. I'm not saying it couldn't happen, but it just strikes me in the gut as not likely. So the fact that the alternator was perfect yesterday makes it hard for me to accept the alternator's to blame. Plus, though my car is a 2013 it's got only 17k miles on it so the alternator should still be pretty much like new.

I've come across plenty of situations, though, where an electronic part works erratically and a failing electronic device could explain why the charging system worked improperly on one day and properly the next. So I'm wondering whether the problem might be with the car's Battery Sensor. The wiring diagram for the charging system consists of only three devices: alternator, battery, and battery sensor wired in series between the alternator's and battery's positive terminals. The battery is brand new, so that leaves only the alternator and battery sensor as likely suspects. As I understand it, the battery sensor measures the current to and from the battery and it's state of health, and the car's computer system adjusts the charging system voltage, idle speed and other parameters to suit. I've read a battery sensor going south can result in low or erratic system voltages. But I'm only surmising here.