jgrill5

Hey guys - I have a new to me 2007 400h awd. When we first got the car, it said it was registering around 26.5 mpg. We reset it and now, after we've had it a couple months, it's registering anywhere between 21.5-22. This does seem pretty low. I don't know if it's because it's been so hot and the ac runs all the time or what.

Something I've noticed is when you're looking at the display in the spedo with whether it's running on engine, battery, or both, it seems to almost always be running on engine. Even when you're taking of from a dead stop and lightly press the gas, it goes straight to engine and no battery. Doesn't seem to matter how much battery power is left, it just does that. Any thoughts? Should I be concerned? I need to take it in for an oil change next month and I guess I'll have them look at it then unless any of you guys had an idea. Thanks!

voodoojc

I have a 2006 400h awd and seem to experience the same thing, but sometimes I can get it to run on electric up to 30mph (downhill). I just reset the mpg a couple days ago. I'll see what I get after this tankful.

mowmow

With Hybrids you really need to change your driving habbits to maximize the use of the traction battery rather than gasoline engine. Try to cruise a bit more, don't floor it all the time, get to the speed you want, let go of gas and gently tap to hold the speed especially in the 20-35mph range, it really makes a difference !!

rcy

Have you tried resetting the ISC (the ISC learning procedure). ISC is the idle speed control. If the battery has ever been replaced, or run down (or even below a certain voltage, the ISC needs to be reset, otherwise the engine idles too much. There is a TSB that explains how the dealer should do it, but it can be done by an ordinary mortal without the dealer only Lexus diagnostic computer.

See here for instructions - http://us.lexusownersclub.com/forums...howtopic=58930

I did this after buying my vehicle used (and then running the battery down fooling around with the NAV system without the vehicle in READY mode).

My around combined highway/city mileage went from 10.2 litres/100km to it's current 8.5 l/100km.

SLegacy99

Check your tires.

jgrill5

Hmmmm, I'll try and see if I can reset the ISC myself. The tires are brand new Goodyears I just put on - I keep them at 35psi....

rcy

The ISC reset is easy. Just make sure the vehicle is warmed up (I had a Scanguage to check, but just drive with a heavy foot and the engine will be nicely heated). The only thing I found was that I could not get the power meter anywhere near 50 to 75 percent. I guess that's to stop you from doing brake stands. Just push down the gas pedal - the engine management computer will not let you get near 50-75, but the process still works.

jrobe

Shut the AC off and drive it for an hour or so on some back roads at modest speeds (< 55 mph) and see what your mileage is. On a warm day, it should be close to 30 mph or something is wrong.

I bet you have a problem. I don't think I could get 21-22 mph if I tried. In fact, I can get 21-22 mph towing my boat.

jgrill5

I reset the ISC. I've only driven it about 10 miles so far...but it's at 31.4 so far, so it's much better. I got the car up to about 25 mph pretty easily from a dead stop on just battery (I haven't been able to do that!). So far, so good.

rcy

I figured as much. I think everyone should reset the ISC and see what a difference it makes. I bet a lot of the techs at Lexus dealerships don't even know about this one.

jpzy3rxh

Is this TSB valid for a 2008 rx400h? I have the 5k service coming up so I can try to ask for this to be done. I have run down the battery to the purple levels a couple times. I was doing 21-23 mpg on 91 octane, but since I switched to 87 octane I'm getting around 25 mpg - it could also be due to warmer temperatures since I switched gas around Memorial Day weekend.

rcy

I think the ISC only needs to be reset if you run down (below 11volts or so or disconnect the auxilliary battery (not the traction battery).

PLamarine

Holy moly! I just got my 2008 400h a few days ago, and the car was on the dealers lot for 3 1/2 months, until they recently dropped the price $5000 (I got it for $7000 below the original asking price). After 2 days, I got the Check Hybrid System message. It turned out the battery had run low, and I brought it to Lexus, and they checked the battery (all good) and charged it up.

I did notice when I was inspecting under the hood right after i bought it that the battery showed that it needed a charge.

I reset the MPG on the NAV, and was getting 23.3 average. Having a few extra minutes to spare, I decided to do the ISC reset as per the instructions, and then I reset my MPG on the NAV again.

WOW!!! What a difference, the engine kicked in almost all the time around town before the reset, and now hardly at all until the battery is about 1/4 charge, then it kicks in. I will update mileage figures after the end of this tank of gas, but what a difference it makes.

mowmow

I thought this TSB only applies to 2006 RX400h, it works on 2007 and 2008 RX 400h also ??

PLamarine

It appears so.