A wierd thing happended this weekend while testing the 4WD capabilities on a beach. This weekend we recieved our first snowfall here and I wanted to try to go out on the beach with my 4wd escape.

I think I understand from some of the road tests why this happens (the computer overrides accelerator requests) but the vechicle when it get stuck seems to not be able to use the full engine power to extricate itself.

For instance I drove a small way off the parking lot to start on trail heading out on the beach. The first part had a small pothole (less than 1'). The vechicle would NOT go climb the pothole even in LOW gear.

when going into reverse even less power.

The RPM's never get beyond 1500rpm. I spent about 20 harrowing mins rocking back forth to get back to the parking lot (I only ventured about 30' off the pavement)

Now it should be noted I did some beach trails several weeks earlier and did not have similiar problems but did not try to drive at slow speeds on the trails.

It shoiuld be noted that the vechicle was NOT hightpointed NOR were the wheels losing traction (as I was directly observing them as I was trying to rock out of the depression/hole)

any thoughts :o

 

I'm not sure about why you didnt have enough power in forward, but In reverse I know why. The way the hybrid system is designed, the faster the I.C.E. moves the more power it robs from the system. A few people have noticed this with the Prius not being able to back up some driveways. Hope that helps.
Cheers,
Steven

 

You are not alone in trying to figure this out. I too have gotten into a position where rpms top out and there I am stuck and rockin and not rollin. I seem to top out at about 2500 and it is after I have been towing a load for awile and am on an uphill. At other times one of my front wheels drops into a hole to the hubs and though I get spin at the back it has pulled out with no problem. I have friends who have had your problem in snow trying to get back on a hard surface.

My first thought is that the 4WD is being automatically locked or disabled because of heat but no one, including myself, has noticed any indicator light in the message center like it is supposed to. I have then turned off the car for a few minutes, turned it back on and run a system check which shows '4 X 4 OK' and I seem to be then able to move forward again. You might try it yourself and watch for indicators.

In darker moments I start to think this loss of power under certainly less than 'extreme off-road conditions' (Ford's language for the override) is the result of a firmware bug in the 4WD sensor of the Powertrain Control Module because it seems to be shutting down my engine for no good reason but not giving me a blinking indicator light like it should. I have gone through the workshop manual but have yet to find a description of this kind of failure.

Perhaps someone else out there has a better idea.

Mike

 

Hi Steve:

___IIRC, the Prius II uses only EV mode to back up?

___Sherpadude, are you saying in one instance (higher speeds) you had power available and in another (slow speeds) you only had partial power? We both know the 2.3 in the Escape even after atkinsonization is worth ~ 130 HP at close to WOT and should be more then enough to pull the Escape out of any small hole or up a < 45 degree incline. I know about the drive by wire and the computer overrides but I have never heard of limiting power when you need it most?

___Sdcatcher, good trouble shooting analysis. I too am interested in the outcome.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___Waynegerdes@earthlink.net

 

In trying to find a pattern in this case versus what I have heard from others when they lose power I have noticed that nobody has said that they lose power when all tires are on level ground. It happens when one wheel is in a depression or on hard ground that causes no slippage.

I heard from some that on level wet or level snowy the response is great. I wonder whether the PCM is shutting down the rpms when the wheel torque reaches a specific high number (caused because the wheels are not slipping). You engineer types out there perhaps can think about whether this theory is on the right track.

Mike

 

Wayne,
Yes, thats correct. The Prius II (and I i believe) use EV only to backup. It has to do w/ the way the PSD directs the power. If the I.C.E. is moving it requires the MG1 to spin more than if it is stationary.
Cheers,
Steven

 

To further elaborate - if this helps ...

During the one day I tested this problem (that I could readily reproduce in those conditions) - I was alternatively level and with a slight gradient (perhaps less than 10 degrees). I could not get above 2k - more like about 1500rpm.

Describing one scenario (access road to beach, with slight snow cover). I attempted to enter the beach got about 10 feet in the road a pair of 10" depressions (someoe before had spun thier wheels to get free). When the front wheels hit this (with speed - less than 10mph) - no problem. When doing the same thing and crawling (less than 5mph) I was not ablle to scale these rutts. No wheels where spinning, one of the rutts could have been deeper than the other I'm not sure, and pushing the gas to floor yielded no more power (1500rpm) than slighty toughing the gas.

I was only able to free myself after rocking back and forth for several mins. It has defintely made me hesitant to use the vechicle in any demanding 4wd situations.

Several months ago I took it out on several beach trips and expierneced very similiar behaviour - if there is no momentum - the car cannot build it (or deliver power sufficient to free itself efficently)

AIM SHERPADUDE2
MSN arnao@interglobal.com

 

I think I may have a better idea why this is happening. I continue to read my Workshop Manual but now am focusing more on the inards of the Powertrain Control Module (PCM) and its Firmware limitations. I print below a section:

Engine RPM/Vehicle Speed Limiter
The powertrain control module (PCM) disables some or all of the fuel injectors whenever an engine RPM or vehicle over-speed condition is detected. The purpose of the engine RPM or vehicle speed limiter is to prevent damage to the powertrain. The vehicle exhibits a rough running engine condition, and the PCM stores continuous diagnostic trouble code (DTC) P1270. Once the driver reduces the over-speed condition, the engine returns to the normal operating mode. No repair is required. However, the technician should clear the DTC and inform the customer of the reason for the DTC.

Excessive wheel slippage may be caused by sand, gravel, rain, mud, snow, ice, or excessive and sudden increase in RPM while in NEUTRAL or while driving.

Mike