Prado 120 Power loss when bogged - Lancelin

[moski Lurker Find all posts View Profile Close moski]

Hi All,

Bought my prado 120 6 months ago and have got into a bit of beach fourbie, but there is an issue. When bogged deep, my baby only revs to about 2k, feels like power loss. Spoke to a mate and he reckons it’s a safety feature so the engine doesn’t #### itself. Anyone else had a similar experience?

Note: new to four wheel driving so have no idea, just winging it.

Pic for reference

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

If you haven't turned traction control off fully by holding the VSC OFF button for more than 5 seconds it will reduce power when spinning the wheels.

If you have turned TRAC fully off, if its an auto it would be trying to protect the torque converter in the gearbox more that the engine by reducing power/limiting RPM particularly if the AT oil temps are high.

Edit: My mistake as amts said there is no VSC OFF on your 120 (a quick look at the manual and the VSC & TRC are automatically turned off when you lock the Centre Diff).

[moski Lurker Find all posts View Profile Close moski]

Thanks for your input mate, i didn’t have it turned off. Will look into it today

[amts Ninja Poster. Find all posts View Profile Close amts]

There is no VSC OFF button on the 120 Prado.

On sand, I would lock the centre diff and reduce tyre pressures to 15psi. You won't get into such a bogged situation very often.

[Daniel150 Member Find all posts View Profile Close Daniel150]

As above. This is VSC. (Vehicle stability control)
VSC limits power if it thinks the vehicle is out of control or sliding etc.
Locking the centre diff will turn this feature off.
This feature will stuff you up in almost any off-road scenario.

A totally seperate feature that works in conjunction with VSC, is traction control.
In a gxl you will have a TC switch as it was an optional extra. In a vx or above you don’t get a switch.
TC simply applies brakes to the free spinning wheel.
Even on soft sand this is still fine, contrary to what you may think, I’ve even found it helpful at times. And yes I do a lot of sand driving.
You can disable all these features by unplugging the abs plug at the brake booster, be prepared for your dash to look like a Christmas tree though.

[Daniel150 Member Find all posts View Profile Close Daniel150]

If you haven't turned traction control off fully by holding the VSC OFF button for more than 5 seconds it will reduce power when spinning the wheels.

If you have turned TRAC fully off, if its an auto it would be trying to protect the torque converter in the gearbox more that the engine by reducing power/limiting RPM particularly if the AT oil temps are high.

Edit: My mistake as amts said there is no VSC OFF on your 120 (a quick look at the manual and the VSC & TRC are automatically turned off when you lock the Centre Diff).

Just to correct…
There is no inbuilt protection for torque converter temps, just a warning on the dash. The vehicle will not cut power, if you ignore the light, you will cook the trans.

Locking the centre diff will not turn off TC. This is done via a button or as I described above.
Locked centre diff and TC on is perfect for 99.9% of scenarios.

Engaging low range will lock the centre diff and turn off VSC.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

Thanks Daniel,

This is what the definitions were in the brake manual that made me think the engine power cut was from the TRC \ A-TRC rather than the VSC:

TRC (Traction Control). The TRC system helps prevent the drive wheels from slipping if the driver depresses the accelerator pedal excessively when starting off or accelerating on a slippery surface.

VSC (Vehicle Stability Control). The VSC system helps prevent the vehicle from slipping sideways when front or rear wheel skidding occurs while cornering.

A-TRC (Active Traction Control). During rugged off-road driving, this system controls the engine output and the brake fluid pressure that is applied to the slipping wheel and distributes the drive force that would have been lost through the slippage to the remaining wheels in order to achieve an LSD (Limited Slip Differential) effect.


I did try to make a correlation between the power/rev cut when bogged Moski was asking about with the VSC/TRC already off and it made sense to me that it would be temperature related and most likely directly or indirectly due to the transmission overheating.

Rationale. The A750 gearbox ECU does have a few attempted protections for controlling overheating which include increasing the shift points, locking the torque converter in 3rd gear and turning the Warning Light On. Because of the common cooling system in the radiator an overheating transmission can also cause the engine to overheat particularly in a bogged situation with limited air flow through the radiator. An overheated engine can cause the fuel and/or charge air temps to rise to the point that the engine ECU starts reducing power output to cool itself and protect the gearbox/drive train if this was a factor in the cause of the overheating.

[Daniel150 Member Find all posts View Profile Close Daniel150]

Cheers mate, I can understand the theory of what you are saying, but in reality it doesn’t work like that.

In moskis case, he has simply not turned off the VSC and so the ecu has killed power to the wheels.

[ptommo59 Senior Member Find all posts View Profile Close ptommo59]

Hi Daniel,

Yep as he indicated that was most likely the case and what I originally suspected .

But I just wanted to explain there was method in my original madness with the second suggestion :-)

[moski Lurker Find all posts View Profile Close moski]

Damn, there may be a deeper issue then, as I had it in Low Range (by what you're saying VSC turned off) too. I had it looked over by a mechanic at UltraTune and he found no issues with it - may be time to investigate a little more. Sand was pretty boggy, but you'd think low range would chew it up and spit it out.

[JohnCW Lurker Find all posts View Profile Close JohnCW]

Damn, there may be a deeper issue then, as I had it in Low Range (by what you're saying VSC turned off) too. I had it looked over by a mechanic at UltraTune and he found no issues with it - may be time to investigate a little more. Sand was pretty boggy, but you'd think low range would chew it up and spit it out.

I'm not sure low range does turn of VSC, certainly on my 2004 I don't think it does. Easy to verify, when VSC is disconnected it indicates so on the dash. But certainly, on sand always engage the center diff which disables VSC. Even on quite hard packed sand VSC can create an artificial sensation the car is bogging into the sand when its just the VSC cutting power as the car moves around.