Hi all,

I bought a 2008 FEH last September (2015). It needed an oil change in January, and I asked the mechanic (independent shop) to inspect everything, as if I was thinking of buying it.

AOK except he reported that it's showing P0A81 DTC. He also said they tested the fans and both work - I assume he means they could force them on via their scan tool. He then said they could not do any repair work on it and I should contact the Ford dealer. After reading this forum I'm a bit reluctant to do that!

The Check Engine Light (CEL) is not on - I assume this is what's meant by "wrench light" in other posts? I don't have the A/N option, just the multi-display for odo, mpg etc in the main dash instrument cluster. It says "Electrical System OK", and when I check for DTC's with my little bluetooth gadget it reports no codes. Is P0A81 a code that needs a more sophisticated scanner to read?

The car does use EV mode regularly, although not as much as I'd like. I think this may be due to the fact that I don't drive it much (it's our 2nd car after our Prius), and the HV batteries don't hold their charge for more than a week or so. I do notice that driving more regularly helps. On a related note, how would a failing 12v battery affect the EV system? I'm wondering if that needs replacing and would help with this. It always starts right up, but I suspect it uses the main EV motor to start the ICE. What are the symptoms of a failing 12v battery?

Finally, I live in AZ and it's been well over 100 the last couple of weeks, up to 114 at times. Seems that the EV mode disables at high temps? It works fine when I leave the house, but driving home in the hot afternoon it doesn't drop into EV mode (after being parked in the sun all day). When pulling away from a stop it's really noticeable - no guts at all!

Being an '08 it's probably out of the 8yr warranty by now, although it's only at 86k miles.

Any comments / suggestions welcomed!
thanks
patrick

 

First thing to do, is when it's refusing to go into ev mode on a hot day, stop and put your hand on the top of the hybrid battery under the cargo area carpet. If it feels hot, like 100F, it means the cooling system for the battery has a problem. 100F is the maximum temperature allowed for the battery. Operating the battery adds heat, so when it reaches that temperature, the system brains disable use of the battery. This is why the FEH seems so gutless when this happens: because you're not getting the electrical boost. If the battery's a/c system is working properly, the battery should be more like comfortable room temperature.

It would use the hybrid battery until the combination of usage and ambient temperature cause the battery to reach 100F. So you'd have ev operation up to that point.

So if the battery is hot, the next question is if the interior a/c is working. If is, the problem is in the portion of the overall a/c system that's only used for the hybrid battery. This would only be some part of the hybrid battery's hvac system. Most likely the fan.

If both the battery and interior a/c are not working, then the problem is in part of the system they both use. That is most likely a loss of refrigerant, but it could be a number of other things, including the compressor, the valve that portions refrigerant between the two hvac systems, or the computer module that controls all this.

An Internet search says the code is for a battery cooling fan failure. This is getting beyond what I have experience with, but I'd guess this is the one located in or near the hybrid battery. I don't think this would show up as a check engine warning.

 

Thanks for the info and suggestions. Next time I'll check if the battery is hot.

Interior AC is fine, although I only use it when I really need to as I don't like AC! Sounds like you're saying that there is one AC system for both interior and the battery. Does that mean that if I have the AC turned off at the climate control, the battery will not be cooled? Or will the computer force the AC on if the battery needs it?

Also, note that the FEH had been sitting in the sun at temps well above 100F for several hours! It's only about a 20min drive home for me, so I can believe that the AC would not get the battery pack down to below 95F in that time.

Final question: If the CEL is not on, and my scan tool shows no codes, how can I see whether there is still a problem - do I need a fancier scan tool?

patrick

 

The a/c system on the pre-'10 FEH could be viewed as a "T" shape. The stem of the T comprises the a/c rad/condenser, belt-driven compressor, and control module. The intersection of the stem and crossbar of the T would be the valve. This valve determines if refrigerant is sent to the interior hvac system, the hybrid battery hvac system, both, or neither.

The interior a/c system would comprise refrigerant lines, fan, blend doors, controls etc.

The hybrid battery a/c system would include refrigerant lines from the engine compartment to the rear hvac unit, fan, controls etc.

Even if the outside temperature is above 100F, the system should be able to get the battery temperature below that, and so enable the ev mode to work. Your drive may, as you say, be too short to get to that point. You should see earlier ev mode operation in the morning. Hopefully your nights are not also at or above 100F.

Turning off the interior a/c will have no effect on the operation of the a/c for the hybrid battery. You have no control over the a/c for the hybrid battery. (Other than reducing overall demands on a system that isn't in optimal operating condition. Like if you have refrigerant, but it's only partly full.) The system will force/turn on the hybrid battery a/c if the battery needs to be cooled and the shared portion of the a/c system is working properly.

To help understand this, I'll tell you what happened to mine. The symptom was that on the first really hot day of the year, I lost ev mode, regenerative braking, and interior a/c. The problem was that the refrigerant lines to the rear of the vehicle corroded through, and all the refrigerant escaped. So both "arms" of the "T" were disabled. In your case, only the rear hybrid battery "arm" is malfunctioning. (Replacing the lines cost me $1800.)

I can't answer the question about the scan tool.

 

I replaced the HV battery fans in my '06. Not an easy job, but quite doable even for a weekend mechanic. About $250 and 2 hours of time. There's a very nice write-up on Edmunds that's linked to here.

The hybrid system is surprisingly sensitive to the 12V battery starting to lose power. If you have any doubt about the condition of your 12V battery, I do suggest replacing it. I put it off in my '06 and I blame that (though I could be wrong) on burning out my Smart Junction Box, which wasn't a cheap repair. This thread includes my description of that experience.

 

Thanks - I found the battery fan replacement guide, very useful. Also the battery blend door actuator replacement guide. When I had the oil change & inspection they said the 12v battery is on its way out, so replacement sounds like a good idea!


I don't want to replace the fans unless they really aren't working - how do I test for this?


I had a longer, cooler drive yesterday and the hybrid system worked properly, thankfully. I could see that the rear AC was working - it was dripping water by the rear left tire, the vent area under the rear floor mat was cold, and I could hear fan noise listening at the rear side window vent. So I guess at least one fan is working. On the way home it was about 102F and the system still worked. So I may have a combination of intermittent issues!


I would still like to know how P0A81 DTC is reported -- my little scan tool says no faults, but the mechanic said he got this code.

 

I'm dealing with this currently on my 07. There's actually two fans in the battery unit. One going bad will throw this code. A typical obd scanner will not detect this code, it doesn't turn on any lights. It'll show on Forscan or any other specialized Ford scanner.

Other AC problems will cause issues with the battery temperature, but this code is specific to fan failure. Even if the fan runs, it has multiple speeds at which it will run. If the motor is worn, it'll create a bigger electrical draw than normal, and create this code. If that's the case, it's not blowing as hard as it should.