Dealer called me a couple of days ago- said it was the MECS pump- they tapped on the pump and the car would start- Ragtop said there is nothing else near the pump (other than the wiring) that could be affected, so I gave them the go ahead to replace the pump. Cost estimate was $680 and change. Later, the dealer tech put the car in the hot sun (110 deg), which was condition where my car would not start. checked it out and found it wouldn't start again. They did some troubleshooting and found a wiring problem- first the service rep said it was a short and then said they had a high resistance reading in the "1876 circuit"to the PCM. Gave me a clue that he didn't know what he was talking about, but he said the car was fixed and ready to go, with an extra charge of $232 for the troubleshooting. I agreed to the charge and said I'd pick it up the following day.
We pick the car up today and service rep swears up and down we will have no further problem. Drove about 3 mi, pulled over to make adjustment on car top carrier (we are on vacation!!!), tried to start car- would not start! Outside temp is about 80 deg- not a heat problem like I've had before. Dealer has made my car worse than when I brought it in! Service rep is apologetic, said they will take a look at it on Monday, since there was no tech on duty today (Sat). He agreed to provide a rental at no charge until the car is fixed. Plan is to pick it up on Tues. Wondering what my liability is if dealer can't fix car- I have to leave this area and get back to work and may have to tow the car back home.

 

The MECS pump could not have an effect on the car starting or not. The computer can't even detect the pump since it's controlled through a relay. The only feedback from the pump to the computer would be that the coolant is over temperature (above 150°F ?) if the pump isn't working.

 

Thanks Econoline, this is what I never understood- how could a pump prevent the car from starting unless there was temperature sensor was in the pump? Do you know what component senses the coolant temperature? The fact that my car would not start in hot weather may mean that the over temp trip point was too low ( faulty temp sensor?) Others have said to check the relay(s) that control the pump. Could the relays fail only in high temperature?

 

If you have a Scangauge you could monitor MeT but I don't know where the sensor is. I think the trip point is 150°F for over temp.

Here's the thread on the relays: https://www.greenhybrid.com/discuss/...hutdown-19843/ One of the relays is the one that controls the MECS pump so it might be worth replacing that one. I think GaryG said there are five identical underhood relays and he recommended carrying a spare (FOAZ-14N089-A $12).

 

Thanks, I'll get the tech at the dealer change this out. So, if the vehicle temp went over the trip point(150 deg?), that would prevent starting? I could see the temp inside the vehicle going to 150 on a hot day sitting in parking lot.

 

I'm not positive, but I would think that it should always start regardless of temperature since the systems cool down by running and circulating the coolant. If still over temp after some length of running time then it would shut down again. I think that was how mine behaved when it went over temp from the MECS pump failure, it would start but then shut down again. The key had to be cycled, which probably cleared the over temp event and allowed the restart.

It would seem like bad design to use any sensor reading from when the engine was off to prevent starting. That's like saying the oil pressure is zero now so let's prevent the engine from starting. I doubt that Ford would do that.

 

What you say makes sense, I don't think Ford would design something that would prevent starting, but these are the symptoms I have had with my 2006 FEH- it wouldn't start only 3 times in high temp in 6 years. Cooling the car down by putting it in shade and airing out the back has done the trick. Dealer was not able to tell my why this could happen, but has this week id'd a bad MECs pump and bad wiring. Now, car has problems starting at any temp- they are still working it.

 

Airing the car out doesn't affect what the MECS cools - that is all under the bonnet. I might guess that the HV battery cooling fans or temp sensors are/going bad.

 

Yes, I learned a lot in the last week about the FEH system, just $900 and 2 years too late. This is not a case of anything just going bad, as this car has had this problem since it was new, I'm convinced. We've only had problems starting in hot weather, and have had the car in hot climates on 3 occasions over 6 years, where it has failed each and every time. The third time I had the luck to have it fail in hot weather while on vacation. The Ford dealer here replaced the MECs pump- I'm not convinced that was really a problem, but I'm told the codes pointed to the MECs. After that didn't fix the problem, the Ford hotline told them to check "circuit 1876" to the PCM. They found damage on the wire in that circuit which gave a high resistance reading- took two tries to get it right, but it looks like that may have been the smoking gun. Nice that Ford tells the tech to replace the most expensive parts first.

FjiordHybrid- what do you know about temp sensors in the rear of the car? That was my thought all along, but nobody I've run into seems to know any details.

 

Honestly, I don't know much about the sensors other than I have read (here, maybe) that some people have had them go bad and need replacing. I think if the temperature sensors in the HV battery go bad it is possible that they can make the computer think the battery is either too hot or too cold to start or at least go EV. I do know that the only things that the MECS pump cools is the stuff in the transaxle and the 12V charger.

I drove from Austin to Las Vegas through really hot weather and never had an issue and I have the original MECS pump.