VTM-4 not working properly?

[Desert Ridge]

Job One for VSA is to prevent vehicle inversion. Terrain was not level. VSA says, "oh-oh, don't want this puppy to tip over, better do something...."

[captmiddy]

Could it be because the system attempted to engage the rear tires and noticed slip and transferred all power to the front wheels which could also do nothing but slip, and really what you needed was power to all four wheels with a little slip to get it to start moving? It is just a guess because it seems odd. But at least you were able to get it to go by using the lock, which is exactly what it is for.

[Webwader]

Could it be because the system attempted to engage the rear tires and noticed slip and transferred all power to the front wheels which could also do nothing but slip, and really what you needed was power to all four wheels with a little slip to get it to start moving?

I don't think so. The only marks on the grass were from the front tires. My fishing partner was watching and he said the rear tires never turned.

[Webwader]

Job One for VSA is to prevent vehicle inversion. Terrain was not level. VSA says, "oh-oh, don't want this puppy to tip over, better do something...."

The ground was not level by a few inches, so the puppy was still wagging his tail.

[Kodiak]

First off, there seems to be significant amount of confusion between the function of the VSA system and the VTM-4 system.

1. VSA= Vehicle Stability Assist. The system uses multiple sensors to determine in the vehicle is maintaining the intended direction you input. It uses a steering wheel angle sensor plus yaw and later g sensors to calculate the actual path vs. the intended path. If there is a significant difference, the system begins taking action. If it is a understeer condition that is due to much power being applied to the wheels, it will begin cutting power and applying brake to the inside wheel. If it is an oversteer condition due to the mu surface or a vehicle response due to a power off from the throttle, it will apply brake to the outside wheel.
2. The system also acts as a full time traction control system. If it detects slip on one wheel, it will divert power to the tractive wheels by braking the slipping wheel. If it detects multiple wheels slipping and calculates you are commanding too much power foe the available mu of the surface, it will begin cutting engine power.
3. As a safety precaution, the VSA system cannot be shut down when a TPMS warning is detected.
Next explanation is the VTM-4 system. First off, it is a predictive rather than reactive system. It ALWAYS launches in 4WD mode. It removes power form the rear wheels when it detects there is no speed differential between the front and rear wheels.

1. The VTM-4 system is always active and can not be shut down unless there is system failure. If a failure is detected, a VTM-4 warning lamp will illuminate in the cluster.
2. The VTM-4 lock button, applies the maximum torque to the rear wheels. If will lock the left and right rear wheels together and therefore should not be used on high mu surfaces. It can only be activated in 1st, 2nd or Reverse gear positions to prevent damage to the rear differential.
3. The system also protects for an oil over temperature condition and will shut down to protect the system.

Next, lets have a lesson in physics: simple beam theory. When a large trailer is loaded on the back of a vehicle, the rear axle load increases. The reduction in tractive capability combined with a low mu surface will result in wheel slip. This will trigger two simultaneous actions: The VTM-4 will increase the torque distributed to the rear axle and the VSA will begin cutting engine power due to the slip condition. If you continue down this path of applying engine torque with the throttle and hold the vehicle at a stall condition, you will overheat the transmission. Additionally, hot engines do not have as much combustion efficiency as an engine at normal operating temperature. The engine ECU will begin retarding the timing to prevent spark detonation and ruining the piston.
Analysis: If you encounter a condition where with a low mu surface and begin to lose forward momentum, you should shut down the VSA system, shift to 1st gear, apply VTM-4 lock, and smoothly apply engine power. This set-up provides the maximum possible driving force at the wheels. If you have applied 20 inch wheels you should be towing – you have killed the available torque at the axle.

Just because the rear axle is not slipping, does not mean the VTM-4 system is not functioning. You may have reached a stall condition at the rear axle due to the available force at the rear wheels combined with the mu of the surface (high axle load improves tractive force) and the reduced engine power caused by the front wheels slipping.

[nevadagarth]

In other words, the situation described to start this thread had put the VSA and VTM-4 at their respective limits for "normal" driving conditions.
Is this correct?

And the only way to "get out of this situation" was to engage the VTM-4 LOCK.
Is this correct?

The combination of trailer load and low mu surface (i.e. slippery conditions) are not considered "normal" so the computer(s) could not compensate for the described condition.
Is this correct?

[Webwader]

Just because the rear axle is not slipping, does not mean the VTM-4 system is not functioning. You may have reached a stall condition at the rear axle due to the available force at the rear wheels combined with the mu of the surface (high axle load improves tractive force) and the reduced engine power caused by the front wheels slipping.

Maybe I should clarify that this occured at a very low throttle position. Since I was trying to get the trailer up on a pair of 2x6's (3" thick) that was only about 18" long, I just eased the throttle on. Front wheelspin occured almost immediately. I eased back off the throttle and tried it again. Same thing. Secondly, the tongue weight of the trailer is only 400 lb. and the bed was empty, not exactly what I would consider high axle load either. I don't buy that explanation. When I did engage VTM-Lock, the trailer went right up on the blocks with a very light throttle and no wheel spin at all. If it is as predictive as you say, it should have sent torque to the rear wheels as soon as it sensed slippage in the front wheels.

[lowrider90]

Originally Posted by Webwader

Maybe I should clarify that this occured at a very low throttle position. Since I was trying to get the trailer up on a pair of 2x6's (3" thick) that was only about 18" long, I just eased the throttle on. Front wheelspin occured almost immediately. I eased back off the throttle and tried it again. Same thing. Secondly, the tongue weight of the trailer is only 400 lb. and the bed was empty, not exactly what I would consider high axle load either. I don't buy that explanation. When I did engage VTM-Lock, the trailer went right up on the blocks with a very light throttle and no wheel spin at all. If it is as predictive as you say, it should have sent torque to the rear wheels as soon as it sensed slippage in the front wheels.

I agree with you, but also agree with he explanation you are responding to. The bottom line, I have tried to spin the front wheels on beach sand and in other soft traction situations have absolutley been unable to do so.

I am going to be hauling my boat this week, 4100 with trailer, and would hate to see the rears not helping as i think they are going to do!, I'll post about that later.

Your rears should have done the job without VTM-$ Locked. Sure would love to hear from a honda Engineer on this one!

[Kodiak]

A 4000 pound trailer typically should be operated with a 12% tongue load in order to be dynamically stable. This reduces the front axle load by approximately 92kg. The rear axle load increases dramatically from 886kg at curb to 1281kg with this type of trailer. That is a 44% increase from the standard axle loads that the VSA was tuned for.

This will probably be misunderstood also, so let’s try to break this down to simplistic terms. The front wheels were on a low friction surface. The front axle load was also reduced by 200 pounds. Both of these conditions combined resulted in the front wheels slipping. This increased the amount of torque being sent to the rear diff. However, when the front wheels start slipping, the VSA will start cutting engine torque. Therefore you got your shorts in a bunch.

Next, why didn’t the rear wheels slip? The rear axle load was increased dramatically. The VSA would have intervened to reduce engine torque when the front wheels slipped. This prevented the rear wheels from ever breaking loose because not enough torque was developed, and the rear axle load was dramatically increased improving the tractive force potential at the rear wheels.

If you simply cut the VSA, the VTM-4 should have transferred the available torque to the rear wheels. As mentioned earlier, if you both cut the VSA, and put the transmission is 1st (not 2nd), and engaged the VTM-4 lock, you have the maximum possible torque available.

My understanding is, once you applied the recommended procedure, the vehicle was able to pull the trailer up the block – correct?

[DoctorJ]

Kodiak, what is "mu"?

And while moving the trailer on the blocks would the rear axle torque have kicked in if the throttle was not reduced? Meaning the VSA did not have enough time to detect the slippage so it could add torque to the rear wheels? I thought that is what you meant when you stated "got your shorts in a bunch".