Have read a number of threads that sound like this ... my 53K mile '06 recently has fallen from low 40s mpg to upper 30s. We are now frequently seeing the battery charge indicator at one or two bars, a point at which there is no motor assist available to help acceleration. Certainly the engine revs higher under these conditions and consumes more gas. This often seems to occur after my wife has come home from work running the A/C full blast. An hour or two later, I get in the car to go somewhere and within a couple blocks the charge indicator is down to one or two bars.

These changes first appeared after two service things we did closely together. First, we put on new Goodyear Fuel Max tires and second, we had a Jiffy Lube oil change with a 5-20 oil (vs. Honda's 0-20). I seriously doubt either of these would make a big impact on FE. A couple of months before this happened, we replaced the 12V battery.

Took the car to the dealer last week, and they could not find anything using their diganostic process/tools. They changed the rear arms and re-aligned the car at that time (again, I doubt this makes much FE impact).

The service writer said they installed all the newest IMA software and I am hoping to see some improvement. It's still a great car at 37-38 mpg, but I cannot understand how it could drop so much (was low 40s). More importantly, I do not like driving without motor assist. Acceleration is significantly reduced and under same driving conditions enough to be dangerous.

I rarely recall the car getting down to one or two bars of charge and motor assist not being available ... only under some unusual situations (for example, a few times I sat in the car waiting for my wife with the A/C running while auto-stopped, and after about ten minutes of that, the charge went down considerably).

I believe the dealer has done the prescribed Honda diagnostic steps, so hoping someone here has been through this and knows what fixes it.

 

Although I have no answer for your concern, as a side note I'll say that I did notice a FE loss of 2+ MPG on my former Camry Hybrid when the dealer mistakenly used 5W-20 rather than 0W-20.

 

Hi Tommy T,

The heavier weighted oil will definitely hit your FE. Make sure you have 0w-20 put in on your next oil change. If anything buy Mobil 1 and ask Jiffy to put it in if they don't have any.

The tires will also have some impact too.

Make sure when you're running the A/C, that you're using the "Auto" and not the regular A/C. The Auto mode is more efficient. My battery pack was taking quite a hit before I realized I should be using the Auto mode. The pack may still take a hit when using the Auto mode depending how low your state of charge is to begin with, but it will happen infrequently compared to regular A/C.

Those 3 things, independently, have a small impact on your FE, but compounded together, will definitely knock it down.

Hope this helps.

Jess

 

I have read a few threads like this one and the end result was the owner was putting in E10 fuel or whatever it is, this is cheaper fuel but gives you less FE in return, this will cause you to step on the gas more using more battery and more fuel. Maybe your wife is doing that?

 

Sitting with Auto-Stop for 10 minutes with the Air Conditioner running is definitely going to deplete your IMA battery. So is a lot of stop-and-go AC use.

I would consider excluding AC use to longer, highway trips where it will be more effective, less taxing on the battery, and the higher speed aerodynamic improvement offset it's impact. The toughest job for AC is getting into a hot parked car, and expecting it to cool things down for a short trip.

When you do use the AC started off in a hot parked car, at least set the temperature higher for the first few blocks, and then lower it gradually as the fan speed diminishes: it's counterintuitive but will cool the car faster.

Per the other posters, using 5W20 will definitely cause a mileage hit. Also, whenever "pros" do your oil change: check the level. If it's above the full line this will also impact your mileage.

New tires? The Fuel Max are obviously LRR, but OTOH when they are brand new they might still be a bit stickier than your old, broken-in OEM's.

 

We're having exactly the same problem with our '06; just got it back from the dealer who says that everything is 'per spec' - yet we're seeing FE drop from 38 - 40 over the 41K miles we've had to car to 33 now; the main battery is seldom above three or four bars, and often at one or two - meaning no assist and a scarily slow car.

I'm escalating the issue, but would love to hear the wisdom of the group...


Marc Danziger
'06 Civic Hybrid

 

As others have mentioned, the new tires and 5w-20 oil will affect mileage. Heavy A/C use and long auto-stops hurt the battery too. High temperatures adversely affect mpg regardless.

I wonder if the battery indicator never gets up to 6 bars or higher that the system is needing a "forced recalibration" or RECAL. These are supposed to be automatic.

I've read that a failing 12V battery can also trigger odd behaviour with the IMA system.

Hope this helps!

Cheers,

Roger

 

Yikes! Something is wrong. Take it in immediately and make sure you get software updates too, if you haven't already.

Jess

 

I experienced this issue for a few months and discovered that my 12 volt battery would only test to 10 volts with a load tester. I replaced it with an Optima D51R yellow top battery and my mileage gained 5+ mpg overnight.

Honda 12v batteries are notorious for failing after 3-4 years. Check there and be sure not to get any old battery as a "normal" battery will draw down the charge from the IMA battery quicker.

 

Mike

How does a weak 12V battery affect fuel economy? My understanding was that the Civic primarily draws upon the NimH battery. If the NimH battery is depleted, it uses the 12V battery to start the car.

Derek