The No-Throttle Lexus (99 GS400 - P1125) 

Fly by night

This issue is probably something the reman supplier either doesn't test or can't test.

Pirates...that's what they are...@##%^

@@sewing1243 That is my opinion also. They may have tested the rest of the ECM engine functions and skipped the one Ivan dug into. I think Ivan is thinking on a much higher level than a lot of other techs. I'm still not certain about his explanation.... but then, I don't mess with Lexus autos either. Thanks again, Ivan, for an interesting video!

The PCM could have a couple different revisions. (speculation). Think about how many engines the PCM must fit into. Mess up the coding for which model and not working. Plus the failure could be the PCM resetting itself into failure mode and never getting out on both.

Precisely correct! I wonder if there's one chip controller or separate transistors that can be replaced?

@@PineHollowAutoDiagnostics It is pretty typical for H-bridges to be a single IC with all four mosfets in it (though discrete fets is possible too of course). The IC is a lot simpler because otherwise you need gate driver circuits and you also need to carefully design your system to prevent "shoot through", where the switching speed of the mosfets is not the same and as a result there is a segment of time where both the high and low driver on the same line are on....blowing up the circuit. Premade ICs handle all that in a reliable way.

Jessica, you are a genius. Impressive take.

@@Zeus-wl2pl I just have an EE background. But, I really have trouble with strange driveability stuff. That is the witchcraft! :)

@@jessicav2031 awesome stuff, Jessica. Now I feel stupid. 😂

Lol they definitely don't have a stellar reputation 😂

Great story! 😃

@@PineHollowAutoDiagnostics It was difficult. Am Asperger's. Don't know how to give up on fact. Ultimately battled falsehood to demise. Oh Well (Peter Green era Fleetwood Mac)...

And your pup too. Hope all is well.

He's a mechanic so it's not like having a someone asking dumb questions and bothering you . . .

It wasn't just for cruise control purposes. There are other reasons for allowing the ECM to control the throttle mapping, like changing the throttle feel or masking the drivability impact of emissions strategies. In some cases like with the BMW VANOS system, much of the throttle control isn't even done with the throttle plate at all.

@@RobertHancock1 It's a dumbass setup, doesn't matter to me what it's used for.

It was informative to try out the replacement ECM and compare waveforms 🙂

Ha it took me a bit of thinking to see the pull up or pull down strategy of the drivers 😉

Exactly! But maybe it did? Service data specifically wants you to test both the motor and clutch winding for resistance (and its actually rather high in, Kohms, so low resistance or a short may cause damage). Unfortunately, no resistance checks were done and no comparisons between the replacement TB vs the original TB. hmm... FS1 may actually determine H-bridge driver damage on both the original ECM and the replacement, concluding that there was in fact a short circuit in the wiring or TB that destroyed both.

@@ecaparts The P1125 clearly has a strategy to disable electronic control during multiple high current scenarios. Not saying it can't still damage the driver but they have done a reasonable job preparing for over current scenarios, from instant transients to more sustained high loads.

@@ecaparts But the new ECM fixed the problem.

@@ecaparts It seems it would have "destroyed" them both the same way. It did not destroy the third one . . .

Had the same problem with them

Financial engineering is where to money is. Lol

If only they ran as clean . . .

What if you DON'T have a known good ECM?🤔

@@PineHollowAutoDiagnostics In general 4-Quadrant (+ regen, sending return spring energy back to the supply) switching (chopper) H-Bridge servo (positional) control for electronic throttle, in satisfying the motor current requirement for torque (and by extension response), is based on a lot of engineering motor and control theory, which is easier to learn (visualize) if you first look at an actual working system and then work your way back to how the drive circuit works and then how the control loop works. What you will find is by looking at the motor current you can see if the bridge is working properly in each operational quadrant with the added dimension of accounting for regen energy from an energy storage source (like a spring, or for a rotational system, momentum) by looking at H-Bridge drive signals. Traditionally, if you look at established 4-year EE degree undergrad coursework you will find a course in Electric Machines and one in Basic Control theory. From a practical standpoint in the motor lab you will first study how a DC PM motor is operated to achieve speed control and then positional (servo) control. I think it is easier to first learn speed control and then move to servo control, although the sequence is largely the professors choice. However, if you just take time and study a working actual system you will understand what the theory is trying to describe. And you are very talented at instrumentation, generically called data acquisition systems. I find a lot of the interaction of electricity and magnetism as a culmination of efforts by Gauss, Faraday, and Ampere as described by Maxwell's Equations, is the long way around when understanding electro-magnetic machines. You don't really have to understand Vector Calculus to understand and correctly apply the theory. If you set up your own experiments you can become very knowledgeable about the practical aspects of motor speed and servo control, and what I think you will find is the primary need to monitor the dynamic aspects of current through the motor windings.

Make a key? Like grind it? 🤔

I'm sure he means programming keys. Lol

@@PineHollowAutoDiagnostics Have you never programmed a key? interesting. You have to go get the physical key copied -- it only costs $1 per key at most hardware stores. But then the key has a built in transponder that needs to be programmed. Some cars like Acura or Nissan require a special code pulled from the computer-- and if the scantool doesn't pull it up, then you can't program the key (which can be really annoying). Newer cars have the keyless system that's more advanced, but I've never programmed one.

That's awesome Roxanne!

Yes the service data and description of operation are lacking here. I am more familiar with GM and domestic vehicles which typically need to be driven open and closed (without power they freeze in position). Not exactly the case with this one. This TB has a strong return spring to the close position. So does it NEED a reversed voltage to the TB motor? NO. Also, there was no reverse voltage indicated on the scope AND the schematic specifically showed the + and - polarity to the TB motor. Does that mean the polarity doesn't change? Unfortunately, I'm left with more questions than answers: Is this NOT an H-bridge driver? What is the clutch circuit for? Why does scan data show TB close % if there is a spring return?? I wish we had more information with this one...

The polarity change is when each wire is pulled to ground/hot. When the blue is high and the red is low, the polarity is going one way, when the red is high and the blue is low, the polarity is reversed.

On a surface it seems that way, but remember, this was an evolution to "drive -by-wire"