drop in fuel mileage and driveability problems after ECM reflash/replacement

Ecfool · 07-03-2007, 02:23 AM

Hope this forum can help before I have to do damage to local Toyota dealer. My wife took her 2004 Prius to dealer for ECM reflash recall, while they were attempting to reflash it they told her that it would not communicate and required a new ECM. Ok fine I told her. But it was running great (average mileage of 45-47, not as good as my Honda Insight but respectiable). Well today after having it back from dealer for approximately 1 week she took me for a drive and said that it was using a lot more gas, I checked fuel mileage gauge, was only getting 23.8 for 120 mile reading, major decrease. The car also will not go to auto stop while in gear and assist is way down as well as synergy battery will not fully charge (only charged to about 1/2 way and still blue on charge indicator after 6 mile drive). Have others had this problem after reflash

narf · 07-03-2007, 02:45 AM

<div class='quotetop'>QUOTE(Ecfool @ Jul 3 2007, 12:23 AM) [snapback]472109[/snapback]</div>

Quote:

Hope this forum can help before I have to do damage to local Toyota dealer. My wife took her 2004 Prius to dealer for ECM reflash recall, while they were attempting to reflash it they told her that it would not communicate and required a new ECM. Ok fine I told her. But it was running great (average mileage of 45-47, not as good as my Honda Insight but respectiable). Well today after having it back from dealer for approximately 1 week she took me for a drive and said that it was using a lot more gas, I checked fuel mileage gauge, was only getting 23.8 for 120 mile reading, major decrease. The car also will not go to auto stop while in gear and assist is way down as well as synergy battery will not fully charge (only charged to about 1/2 way and still blue on charge indicator after 6 mile drive). Have others had this problem after reflash
[/b]

Some of what you mention is normal...

The battery is supposed to stay around half full on average. You shouldn't see full green unless you spend several minutes coasting downhill. Also, I found on my car that the first tank or two after a reflash I had reduced mileage, down to about 42 from 50. The car is recalibrating to the battery system.

As far as the engine shutting down, if it is extremely hot out, extremely cold out, not warmed up yet, or if the A/C is running hard with a low battery the engine will keep running to maintain the battery.

How's the weather, and how long are the trips you are taking, and how are you calculating the mileage?

**efusco** · 07-03-2007, 08:41 AM

23 is very low and definately suggests a problem that only the dealer will be able to diagnose/treat.

But, before you go, check a few things:
1)Tire pressure. The only time I've seen dramatic drops was when I had one tire going flat and the pressure was very low.

2)Oil level...probably not it, but check it anyway.

3)Make sure the defrosters aren't on/running continuously.

I agree that the battery SOC doesn't sound like a major problem. If it was frequently dropping into the pink range I'd be concerned, but 4-5 bars is normal.

If the issues persist with mpg 1/2 of what you normally get they definately need to check the car out.

**TonyPSchaefer** · 07-03-2007, 08:49 AM

I agree that it sounds as though something odd is going on there. Do what Evan suggests.

What strikes me is that with the engine running as much as you say and the reluctance to go into electric mode, I would expect the battery's state of charge to be much higher than a half. I mean, when the engine's running it's usually recharging the battery in some way. Not always, mind you, but some of the time. And with it running as much as you indicate, I would think that there would be a considerable amount of regen going on.

We should also consider that the Prius really does "learn" the driving style of the owner. Unfortunately, all this memory goes away when the 12v battery is disconnected. Therefore, the first thousand or so miles after a disconnection will see lower-than-normal mileage.

Keep us posted.

Ecfool · 07-03-2007, 12:04 PM

Thanks for the replies, as a hybryd driver since 2000 (bought Honda insight #116 off assembly line) and proffesional mechanic. I check tire pressures at least weekly maintain 40psi, oil level checked weekly. I even tried a scan for diagnostic codes no codes present. As for "learning curve" sorry not buying that theory, I know as in Honda IMA that if you dissconnect 12volt battery you loose all battery charge indicator so yes some recalibration for state of charge. The main battery does loose charge while driving, it will drop from half to only 1 bar rapidly then slowly build up. I am aware heat will affect state of charge and it has been approximately 115 out lately, but it hasnt done this in previous summers or even before ECM replacement. My biggest concern is lack of power and really really low mileage. Called dealer today and got appointment for friday so may have answer then.

07-03-2007, 08:41 AM	#3
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 17,250 My Car: 2004 Prius Model: Package: #9 Thanks: 50 Thanked 261 Times in 157 Posts Friends: 37	23 is very low and definately suggests a problem that only the dealer will be able to diagnose/treat. But, before you go, check a few things: 1)Tire pressure. The only time I've seen dramatic drops was when I had one tire going flat and the pressure was very low. 2)Oil level...probably not it, but check it anyway. 3)Make sure the defrosters aren't on/running continuously. I agree that the battery SOC doesn't sound like a major problem. If it was frequently dropping into the pink range I'd be concerned, but 4-5 bars is normal. If the issues persist with mpg 1/2 of what you normally get they definately need to check the car out. __________________ Evan E. Fusco, MD "It's a damn poor mind that can only think of one way to spell a word." -Andrew Jackson

07-03-2007, 08:49 AM	#4
TonyPSchaefer Your Friendly Moderator Join Date: May 2004 Location: Far-North Chicagoland Posts: 10,512 My Car: 2004 Prius Model: Package: #9 Thanks: 39 Thanked 168 Times in 109 Posts Friends: 23	I agree that it sounds as though something odd is going on there. Do what Evan suggests. What strikes me is that with the engine running as much as you say and the reluctance to go into electric mode, I would expect the battery's state of charge to be much higher than a half. I mean, when the engine's running it's usually recharging the battery in some way. Not always, mind you, but some of the time. And with it running as much as you indicate, I would think that there would be a considerable amount of regen going on. We should also consider that the Prius really does "learn" the driving style of the owner. Unfortunately, all this memory goes away when the 12v battery is disconnected. Therefore, the first thousand or so miles after a disconnection will see lower-than-normal mileage. Keep us posted. __________________ Proud father of Priapus: the '04 Tideland BC9 with an OEM EV button and sense of self-righteousness Current Mileage Chicago Prius Group Website Chicago Hybrid Group on FaceBook Find me on faceBook

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07-03-2007, 02:23 AM	#1
Ecfool Join Date: Jul 2007 Posts: 2 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Hope this forum can help before I have to do damage to local Toyota dealer. My wife took her 2004 Prius to dealer for ECM reflash recall, while they were attempting to reflash it they told her that it would not communicate and required a new ECM. Ok fine I told her. But it was running great (average mileage of 45-47, not as good as my Honda Insight but respectiable). Well today after having it back from dealer for approximately 1 week she took me for a drive and said that it was using a lot more gas, I checked fuel mileage gauge, was only getting 23.8 for 120 mile reading, major decrease. The car also will not go to auto stop while in gear and assist is way down as well as synergy battery will not fully charge (only charged to about 1/2 way and still blue on charge indicator after 6 mile drive). Have others had this problem after reflash

07-03-2007, 12:04 PM	#5
Ecfool Join Date: Jul 2007 Posts: 2 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Thanks for the replies, as a hybryd driver since 2000 (bought Honda insight #116 off assembly line) and proffesional mechanic. I check tire pressures at least weekly maintain 40psi, oil level checked weekly. I even tried a scan for diagnostic codes no codes present. As for "learning curve" sorry not buying that theory, I know as in Honda IMA that if you dissconnect 12volt battery you loose all battery charge indicator so yes some recalibration for state of charge. The main battery does loose charge while driving, it will drop from half to only 1 bar rapidly then slowly build up. I am aware heat will affect state of charge and it has been approximately 115 out lately, but it hasnt done this in previous summers or even before ECM replacement. My biggest concern is lack of power and really really low mileage. Called dealer today and got appointment for friday so may have answer then.