Originally Posted by
harlie
Exactly Gav! This is the big problem with electronics and peoples blind reliance that electronics are great – well not this exact example but the notion of everything that is reported must be gospel (bit like the media really).
Now, as some here know, I’m the biggest fan of electronics, I’ve got a habit of converting everything electrical in sight to run a programmable integrated interface – just for the hell of it. Several years ago, my wife asked, “why do you need to be able to turn the kitchen light on/off from anywhere in the world?” I replied “O come on, you don’t think it’s cool that an internet connection in London can click a button that sends a command that is transferred through several different protocols, over several mediums including a standard 240v power line to operate a tiny relay hidden in the wall within a couple milliseconds.” Eyes were rolled as she walk away - she does quietly think it’s cool that she can turn the heating/cooling on or off or just check the inside temp at home, or the pool water temp from her desk at work in the city (or phone on the way home) before she plans her evening! Anyway back on track.
Problem: Assuming that all electronic/electrical issues will log a fault is very naïve – it’s an idealistic notion but that’s it. After reading uteman’s posts I am assuming that he’s NOT a moron. The Electronic Control Modules only log faults for issues/errors/scenarios that they know about, someone has to write the code that executes - firstly in the event of a fault occurring (input from sensors or network data values are identified by the main program), and secondly the entries (fault detail) that are logged. If the ECU receives an analogue value from a sensor or digital value from the network that the original designer did not consider would be received then 2 possibilities commonly happen, either it handles the exception and a vague fault is logged (no or incorrect details recorded) or nothing (the car continues as if nothing is wrong – the computers are oblivious to the issue). I’m trying to ignore the 3rd possibility of unhandled exceptions, which would have the chance of creating a really unpleasant scenario.
What uteman describes here (no one else has seen/heard/felt what’s going on), is typical of the system being oblivious. This could well be a drive train issue, but personally I don’t think so - the lockup should be smooth enough to not cause a drive train shudder and if it is drive train I would think you would feel something during normal gear changes as well. However like vehicle computers, I have ‘returned’ incorrect advice in the past and could be wrong here.
As an example of issues that the ECUs won’t record think about this. The Trans computer (TCU) sends a request to the Engine computer (EMS) when lock up is required. The EMS receives this and reduces engine torque (to allow smoother change) at the same time it sends a message back to the TCU with timing details. TCU receives this message and times the signal (to the millisecond) to the lockup solenoid. The signal to the lockup solenoid is analogue (the TCU outputs voltage from +0.5 to +12v on a dedicated wire which is earthed somewhere – this wire is different to the wire that engages each gear change).
If this wire (or connectors) has extra resistance for some reason (dirt/grease/oil/rust) the voltage received by the solenoid will be vastly lower than expected – Or what if the circuit board/capacitor/mosfet ect (inside TCU) has deteriorated to the point where it is actually outputting lower/higher voltage. Does the solenoid open/respond at the same speed with reduced controlling voltage? Don’t know, but I do know that there will not be a fault logged in any ECU for an example like this, firstly the developer would not have considered it and secondly the TCU is not monitoring what is received by the transmission.
Gav’s point of the injector above is great – the EMS does not check whether the nozzle piezo opens, let alone how much fuel is squirted in. It just checks that a circuit is plugged in and able to receive voltage – it could even be a small resistance short because that check has no redundancy.
These types of scenarios highlights the problem with Computer controlled mechanicals, and it’s not limited to cars. Everything that is controlled by computer where the final output is not monitored with redundancy is prone (down to simple things like my pool heating, computer told the valve to open diverting water to the roof for heating – someone (me) had accidentally cut the wire while gardening so that signal was never received by the valve – computer was happy the pool was heating – mrs wasn’t!).
This is the issue I have with computers in modern cars; there is no where near enough monitoring for the electronics to provide complete diagnostics – we all hear stories about funny errors solved by replacing a sensor. The problem is compounded by the attitude of many people (including dealers & mechanics) that the electronics always report everything and accurately. There is no where near enough focus on signal/data checking.
In short a fault is only logged for an error that the ECU receives and expects.
If it was me (because this is my field) I would be checking that the messages between EMS and TCU are indeed on the BUS and that their timing matches. Then check the analogue signal and comparing them to another vehicle. Unfortunately that is above most mechanics – just like rebuilding a transmission and torque converter is above me.
So it’s not the Transmission, Maybe try another TCU and check the wiring loom and every connector.
I’m sorry to hear your pain uteman – I was there with our D2 some 10 yrs ago while still under warranty, after every sensor, loom and injector was replaced, they replaced the EMS and the weird problem was gone, ironically it was torque converter related (only partially lock and then would get surging)… At the time I had a dealer mechanic tell me that it “couldn’t possibly be a computer issue because the other computers would log errors.” I responded as would be expected, I remember being so crapped off with it I wouldn't look at it…. Other than sensors the engine and transmission wasn’t touched, it was a near new car – we still have it, trouble free.
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