Haven't had luck finding any info on this anywhere, so I've been trouble shooting by myself so far. Here's the problem:

Twice in the last 6 months, our S60 has experienced a complete loss of all electrical systems while driving in extreme heat (100+ degree weather.) This is what has happened in both instances:
1. a/c begins to run hot
2. engine becomes sluggish
3. instrument warnings start popping up one after another (trunk lid open, passenger door(s) open, brake failure warning, etc.)
4. headlamps / signal lights fail
5. door locks and windows fail
6. and ultimately, complete failure of the instrument cluster (and all accessories.)

At this point, the car will continue to run. However, once the vehicle is shut off in this condition, it cannot be restarted by ay means (even a jumpstart) unless:
1. it is allowed to cool
2. the battery is disconnected and reconnected.
battery and alternator have both been tested and check out fine. engine is not overheating either. only a disconnect / reconnect will restore electrical power and the car can be started normally without the aid of a jump Continuing to drive in the heat will result in another shutdown, but driving in cooler weather the car will run fine as if there never was a problem.

after digging around under the hood and checking every power terminal i could find, i finally took apart the ECU box (under hood, right front fender side, just forward of the power steering pump) and discovered that the closed box is fed by an air tube leading back to the cabin / firewall. on the box end, there is a 12v fan feeding air to the box similar to what you find in your pc / video card.

After dissambling the 12v fan housing, and starting the car, i have found that the fan does not operate. i was thinking the fan could be temp controlled, only kicking in at higher temps. but if that's not the case, have i found the potential problem, a busted fan? has anyone else run into this before?

 

temps finally hit 100+ in parts of L.A. this afternoon...
and sure enough, after sitting in the sun and 100+ temp, the car died this afternoon after about 10 minutes of driving, leaving my wife stranded when she parked and shut the car off. The car has driven perfectly fine in lower temps since the last incident nearly two weeks ago.

Exact same symptoms, same fix. I popped the hood, opened the housing for the ecm. the module felt a bit hot to the touch, but it didnt seem too extreme? anyway, i let the car cool, disconnected the battery, reconnected, and the car drove home like nothing happened.

what gives?

 

2nd day of temps, second consecutive day AGAIN with the problem. This time I got my hands on it mid day while it was still hot. All the electronics shut down after 2 blocks, but the car made it the rest of the way home (about 10 miles.)

1. the ECU cooling fan DOES operate.
2. the ECU unit was burning hot to the touch, even after the car cooled in the garage
3. opened the under hood fuse box... all fuses are fine, however, the ECU relay was burning hot to the touch; i couldnt keep my finger pressed on the top of it.
4. i have been unable to find any loose connections, bad grounds, or melted wires.

i read on another forum that a remote terminal under the hood can have issues (bad solder/connection; can cause a break in the line between the ECU and fuse box in high heat.) i found it, but it's located at the front engine mount and nearly impossible to reach/examine without removing the radiator fan.

all i know right now is the car will 100% suffer a complete electrical failure in the heat. does ANYONE out there have a better idea what the issue could be? it's gotta be electrical, but WHAT and WHERE?

 

i have a 2001 c70 that went through a flood, their is no power at all. this car is new to me and i need to fix it. what could it be? ecm? did you figure out what caused your volvo to die in high heat

 

I had the ecm moule replaced when I had the same issueyou describe. I haven't had any problem since>

 

Is the Alternator still charging good when it gets hot?
I will bet it is not.

 

yeah, we had the car hooked up when it was good and hot in vegas (109F, which was one of the 2 times i was referring to in my OP) ....alternator was charging fine, battery voltage was fine too. got it back on the road and crapped out again at state line.

as far as the ECM, yeah, that's something i've been thinking too. it's pretty damn pricey though, and if that's the case, i'm inclined to just let it be over the winter.

we did have ONE more hot day where it happened again. same story. car died once it was shut down in the garage, but the ACC position still worked (sort of. dash would light up, but was dim, and door locks wouldn't work.) I unhooked the post under the hood, reconnected it, and it started right up fine.

so, it's still a mystery. the only other thing strange this car has done is that it's blown three low beam bulbs (2 left, 1 right; all silverstar bulbs) over the past year in cold, damp weather. so, electrical short, ecm.... $*&^ i don't know...

 

ecm - silverstar bulbs are known to blow in that condition so i doubt it is related.

 

Maybe the connection at the post under the hood is causing the problem.

 

I'm wondering what the fix for SoCalS60 was. I have a 2004 S60 2.5T doing the same thing. Hot, humid days I can get about 5-10 miles out of it before the clock goes to dashes, relays behind the dash click, all gauges and dash go dead and the car goes into the "limp home mode". Sometimes it will set the CEL and the SRS Airbag light is set. I've also seen the "brake fluid low" message, and "brakes failed, stop safely" message but these are intermittent and do not happen in conjunction with the dash blanking. When the dash goes blank I also lose power to the power windows and locks unitl the car sits and cools down. I've had the car since new and all of the recals are complied with that I know of including the fuel psi sensor, module software updates, etc. It is a temperature related, wiring/circuit board issue. I'm leaning toward the Autobrake Control Module but haven't spent the $$ yet. I haven't found any forum that gives a definite fix for the issue but have found several posts with the same issue, included the NHTSA site. Any insight would be appreciated.

 

This may be a dumb question but, is the tube that runs from the ECU box to the radiator still connected? I know this tube routes cooler air from the front of the car to the ECU to cool it. May be something as simple as that.

 

Checked the cooling air tube you mentioned. Looks like this model vents air from the a/c compartment(interior) via tube into the ecu box and then overboard under the car by a second tube. With the car running I could feel the cooler a/c air circulating. I'm leaning more towards the Autobrake Control Module because of the intermittent "brake fluid low" and "brake failed" messages.

 

im working on a recently flooded car and am fighting through some of the same issues ya'll are describing. the error messages on the dash are the same. i found i got some things working by removing the CEM and hosing it down with a circuit board spray/cleaner, called HILCO LUBE by Hill manufacturing.(no i dont sell it). it brought the dash back to life. Car ran even though dash was dead. if i find any more solutions, i will post them.

 

Sorry to revive the dead, but I've got what seems to be an identical problem with a 2004 v70. This (limp home) ONLY happens when we get 90 degree plus temperatures. Has anyone ever figured out a fix...or even the exact problem?

 

I too would be interested if anything ever came out of this discussion.
Our 2002 S60 runs great until the outside temps get hotter than 90-degrees than it goes into the limp mode.
Let it sit for an hour or two and she runs fine ... Till she gets hot again.
Other than this aggravating issue, it runs great.

Thanks in advance to any advice ... Next step is back to the dealer who has yet to resolve issue!!!!

 

Problem Solved .. For those interested I discovered the throttle plate was binding upon full engine warm up.
With the aid of a heat gun, I removed the ETM, sat in on my workbench and slowly applied heat to the throttle plate and surrounding body.
Discovered the plate would bind at elevated temperatures ... Lossened up the throttle plate screws and allowed it to reseat itself.
Tightened the screws back up, reinstalled the ETM and now back in business!
Car drives the way it should without taking it to the costly dealership!!

 

I am having issues with my V70, and trying to tackle it down do you mind offering more info as to where the throttle plate and the ETU is?

 

My issue was strictly due to the throttle body itself causing my S60 to go into the "limp-mode".
Original post/discussion was possibly ECU module related.

Both units are "located under the hood" ...Both noted problematic issues perhaps related to heats.
ECU module is located in an "L" shaped plastic black box ... Throttle body plate located within the throttle body itself, sitting directly in front of engine with air intake hose connected from air cleaner.
In my case, excessive under hood heat combined with elevated outside ambient temperatures caused my issue.
If your vehicle is going into the "limp" mode during hot days, take a look at your throttle plate (located in the throttle body itself.. metal flapper blade) and see if it can move freely.
Mine was binding in the "closed"/Idle position.
This may be a bit tricky to test for as it was only noticeable when everything was fully warmed up & hot.

 

It was something affected by heat/humidity so the throttle plate could have been the trick. Don't know if the throttle plate would have been the fix for the my issue since I kept getting the "brake fluid low" and "brakes failed/stop safely" messages in conjuction with the limp mode and dash blanking out. I tried a junk yard antiskid/abs module but the car acted up again after a few months...reinstalled the orignial abs/anti-skid module. I also resoldered all of components on the dash module(fix for a similiar issue) but that never helped either. I went to several dealers and one of the best Volvo shops(had it towed but they couldn't duplicate the next morning). The dealerships all wanted to replace modules, that worked fine 95% of the year. I thought it could have been the CEM board but that is in a conditioned enviroment and spraying it off with cleaner wouldn't have done much, based on past expirence. I worked this over three summers and finally got rid of the car. Hated to do it as it was loaded car and paid off but I was tired of dealing with it stranding my wife/kids at the worst times/places and not having enough time to work on the car myself. I got rid of the car before dcdlexmass posted his first post. Good luck.

 

I worked this over three summers and finally got rid of the car.

Perhaps the most intelligent comment to date!! .... After repairing my daughter's S60 throttle body issue this summer I was once again reminded why these cars are such a PIA.
Brake light failure warning and a check engine light went on just last week! ...
Indeed they are wonderful cars when running correctly but they sure need a lot of TLC and $$$$$$.

We will be looking to replace it soon as I find some spare time!