Question for TECH-- Acceleration Sensor AND FLASHING ARROW
#4
06-02-2011, 10:04 PM
#5
06-02-2011, 10:08 PM
#6
06-03-2011, 05:52 AM
I don't really understand the question/statement but I think you are asking if the speed sensor will cause the car to go into the "LIMP HOME" mode. The answer is yes. And you don't have to drive it for a while for it to drop into "LIMP HOME" mode.
I have been having major transmission problems with my wagon. The crazy thing about it is that it's been getting better, not worse.
The transmission computer is programmed to change gears at certain speeds. There are certain throttle positions as well as vehicle speeds & loads that trigger the shift points. When the conditions are right for a shift and the computer sends the signal for a shift to occure and the shift doesn't take place, the computer considers that a problem and triggers the fault and kicks the car into "LIMP HOME" mode. The tranny computer doesn't want the tranny to get damaged and creates the fault notice to protect the tranny. This will also happen (the fault detection) if a signal is not received. An example of this is, 4 out of 5 signals are present and the 5th one doesn't happen in time. The computer will assume that something is wrong with the 5th item, like the speen sensor, then toss the fault code and go into protection mode to force you to get the system checked out.
The thing about the "LIMP HOME" mode is that it limits shifting and causes you torque, power and ultimately gas mileage. I just put about 2,000 miles on this wagon with the tranny tossing all kinds of codes, slipping gears like it's driving on pudding, and all sorts of shifting problems. The day before yesterday the car was doing pretty well on a country road and I looked down and there was a little surprise at the "flashing arrow". I decided not to reset the code and a few starts later the arrow disappeared and the car started preforming better (still had the CEL). I pulled the codes from my OBD-I port the next morning and got about 7 codes. I then pulled codes from the OBD-II port and only got 1 code, the dreadded P0730.
The first thing I think you shoud do is flush/change your fluid if you are not sure if it's been done within the past 30,000 miles. If the fluid is old it could be causing the gears to stick together a little or something.
I have been having major transmission problems with my wagon. The crazy thing about it is that it's been getting better, not worse.
The transmission computer is programmed to change gears at certain speeds. There are certain throttle positions as well as vehicle speeds & loads that trigger the shift points. When the conditions are right for a shift and the computer sends the signal for a shift to occure and the shift doesn't take place, the computer considers that a problem and triggers the fault and kicks the car into "LIMP HOME" mode. The tranny computer doesn't want the tranny to get damaged and creates the fault notice to protect the tranny. This will also happen (the fault detection) if a signal is not received. An example of this is, 4 out of 5 signals are present and the 5th one doesn't happen in time. The computer will assume that something is wrong with the 5th item, like the speen sensor, then toss the fault code and go into protection mode to force you to get the system checked out.
The thing about the "LIMP HOME" mode is that it limits shifting and causes you torque, power and ultimately gas mileage. I just put about 2,000 miles on this wagon with the tranny tossing all kinds of codes, slipping gears like it's driving on pudding, and all sorts of shifting problems. The day before yesterday the car was doing pretty well on a country road and I looked down and there was a little surprise at the "flashing arrow". I decided not to reset the code and a few starts later the arrow disappeared and the car started preforming better (still had the CEL). I pulled the codes from my OBD-I port the next morning and got about 7 codes. I then pulled codes from the OBD-II port and only got 1 code, the dreadded P0730.
The first thing I think you shoud do is flush/change your fluid if you are not sure if it's been done within the past 30,000 miles. If the fluid is old it could be causing the gears to stick together a little or something.
Last edited by rspi; 06-03-2011 at 07:28 AM. Reason: edit
#8
06-04-2011, 09:52 AM
#9
06-04-2011, 07:38 PM
He's talking about the vertical acceleration sensor located on the engine cradle. Doesn't normally have anything to do with the trans, but strange things can happen and throw a car into limp home mode.
#12
06-06-2011, 08:53 PM
It's located on the front of the engine/ suspension cradle, on the passenger side. Little squarish flat black box bolted to the front of the cradle. It's an accelerometer, and it senses up- and- down movement of the car- specifically, hard bumps or potholes- and sends that information to the computer. That way, the computer can differentiate between engine pinging and road bumps, so that it doesn't unnecessarily retard ignition timing. Basically, if the computer gets a signal from the knock sensor(s) at the same time as it gets one from the vertical acceleration sensor, it knows it can safely ignore the knock sensor signal. It's kind of a weird, Volvo- specific thing (at least I've never seen one on any other car) but it's still an ingenious idea to get the best performance possible.
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