This post is long so I am going to summarize what I noticed first and then go into detail below. Also I have searched this board and others but if what I am describing is old news and I missed it please forgive me:

I took my 06 in last Wednesday July 25th for the backseat/battery recall and because I felt that my IMA battery was not regenerating as it should. They told me everything was fine with my battery and system but there was a PCM update available for the car. I have noticed a significant change in the way the car operates since. Here is the summary:

1.)After the update I notice an improvement of about 2 mpg on my average.
2.)I achieve this without having to “hypermile” as aggressively as before
3.)The EM assist is much more prevalent and remains constant throughout the entire acceleration-time and distance of acceleration no longer matters (similar to how the Prius operates).
4.)Essentially the IMA now replicates what we hypermilers call “assist” during acceleration and without going through the 4 steps you normally have to enter the “assist” mode.
5.)The level of SOC is not as important as it used to be
6.)With the changes it is much more difficult to attain a maxed out (7 or 8 bars) SOC (but as stated in number 4 this does not hurt me nearly as much as before).
7.)Keeping the Instant MPG over 70 when gliding and assisting is a good bit easier
8.)Cruise Control appears to give a better average MPG then before ( I have not had a chance to test this out extensively yet)
9.)My invoice from the dealership said “updated PCM, Electric motor and IMA battery software” but gave no item number or code and the folks at the dealership had no specifics.

Okay here are the details:

First let me give you a little background on myself.

-I purchased my HCH II in May of 2006
-My average since January is about 51 mpg per tank (I don’t log much of my mileage on this site, I have been using atlantagasprices.com for years now)
-I currently have 19k on the vehicle
-I rarely use AC,
-Tire pressure is between 44 and 46psi.
-My commute is 80% city 20% highway
-I disabled my DTR lights.
-I drive with my shoe off.
-I installed an engine block heater last winter (did it all by myself-proud to say that but it was hard!)
-I have been on this site since I bought the car but didn’t start posting much until about a month or two ago.


Okay so here we go. As many of you hypermilers know managing your SOC and staying below 2000/2500 RPM’s are two of the most important things in achieving a high average MPG. My experience is that the SOC matters very little since the update a week ago.

Before the update the amount of SOC determined how much assist the electric motor would give when starting from a dead stop or accelerating while moving. In either situation the electric motor would lead, the gas engine would follow and the electric Assist would retreat to nothing. I would accelerate until the RPMs hit 2000 and then either go into assist or glide mode if I could.

Now the electric motor assists 10 times more then it used to. What I mean by that is that during any period of acceleration irrespective of whether you are stopped or moving the electric motor no longer retreats to zero. Let me explain:

At 4 bars or above SOC the EM will assist 100% upon acceleration and retreat…but no longer to zero. It will hold and maintain at least 2 bars during the entire acceleration-no matter how long that is (so long as you have at least 4 bars of SOC). Also before when moving I didn’t have to necessarily punch the accelerator but had to apply a decent amount of pressure for the EM to reengage and assist again. That has completely changed now. To sum it up the EM will reengage and respond to the faintest amount of increased pressure on the gas pedal. So much so that when I glide I sometimes slip into assist without trying at all (I prefer gliding to assisting to preserve my SOC). Also, I rarely get the 1 bar of regen when moving anymore at all unless I really try (I learned that the one bar of my regen was my friend and not my enemy. Remember I am mostly city and don’t get the chance to regen as much as I like).

Most importantly I have notice that the amount of “constant” assist is tied loosely to the SOC. It is usually 2 less bars of assist then your current SOC. So when I have 7 bars of SOC the IMA retreats to and maintains 5 bars of assist until I complete my acceleration. 6 SOC=4 bars of assist and 5/3 and 4/2. Under 4 bars of SOC it reverts back to its pre-PCM update method of the EM leading, the gas engine catching up and the EM retreating to zero.

There is not much highway driving during my normal commute so I made a special trip to the interstate to test it out. On the way I notice that I did not have to crawl away from a stop light when it turned green to protect my average mpg. I could accelerate almost as much as if I were in a normal car and not hurt my mpg so much (reaching an unheard of 3000 or 3500 RPM’s). On the highway I got up to 65, slipped back into gliding for a while and then accelerated some again. At the time I had 7 bars of SOC. With the slightest touch I the EM reengaged to near max and settled at 5 bars of assist. I kept my foot pressure steady for a long time and the EM kept assisting. I didn’t count the time but I went a very good distance and ate up 2 bars of SOC. The EM never stopped assisting and I quit accelerating myself since I value a high SOC so much. Now let me clarify that I am not talking about nor did I employ well known “assist” technique ( reaching a certain speed, taking foot off of pedal, maxing out the instant MPG, allowing the gas valves to close and lightly applying pressure to the pedal to gain assist bars from the EM until just before your reach the breakpoint.) This was accelerating out of the glide, passing the breakpoint, the valves opening back up with the instant MPG around 40.

The only downside is with the new update my SOC stays around 4 or 5 (remember I have very little highway). When I glide I easily slip into assist without trying. I never get the one bar of regen and it is more difficult to regenerate the SOC since any acceleration now automatically reengages the EM. As I have described this isn’t so bad but my SOC has bottomed out once and I never used to let that happen before the update (remember I don’t run the air conditioner).

Lastly I have yet to see the results of the update on a brand new tank of gas and a freshly reset trip meter. When I took the car in I had about ¾’s of a tank and a trip average of around 52 mpg. When I picked it up at the end of that same day the kind tech that worked on my car at the dealership had the air on full blast and must have floored it because he dropped it to 45.5 (over what looked to be about 5 miles of driving). In the week since I have manage get it back up to 48.9 and have about 2/5’s of a tank left and somewhere in the middle 300’s in regards to miles on this trip

I think I have covered most everything but if you have any more questions let me know. Also if anyone else has had the update are you experiencing the same thing (I have seen one other person allude to it)? I found a thread here talking about a PCM update that came out in March of 2006, but I didn’t see any description of that one doing what I am describing and I am inclined to believe that what I have is a 2nd-more recent update.

Anthony

 

Interesting. I have noticed steady increases in my mileage over the past few tanks, but the last tank (the first after the first oil change) has been stellar. I posted a few days after the oil change with an observation that it is easier to get into the higher points on the instant FE meter and my mileage on that tank was an astounding 58mpg in combined suburban and mountain driving.

I just checked the maintenance slip from the oil change and there is no reference to a PCM update on the ticket (although that might not mean anything). BTW, I had the battery cap replaced about 4 months ago and didn't notice any stellar improvment after that.

I'm curious to see what other owners say on this thread--especially those who have had their cars serviced recently...

 

Well, I haven't had my car serviced recently, but I do have a 2 mo old HCH. It operates much like you are describing it, so I'm assuming that it came with the PCM update.

 

Do you have a Bulletin # or something? My SA can't see that my '06 needs an update.

Thanks.