The terms EMS (engine management system) and ECM ( engine control module) are one and the same ;)
It's easy if you understand how the data systems work ;) The ECM receives the ambient temperature from the instrument pack via Can-bus it also sends it to the HEVAC. Because of the failure of the Can-bus controller in the EMS the data packet sent by the instrument pack gets no response from the EMS and can no longer see the ambient temperature as being valid. Because the HEVAC then also doesn't get a valid ambient temperature signal it won't let the HRW work. It will also effect the ambient temperature signal on the K-bus to the BCU also as the instrument pack converts Can-bus to K-bus, the DS2 bus as well as the window bus and Nav-bus (if fitted) ;) Can-bus data always takes priority over any other data bus. Russ |
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The CANBUS signal from the ECM is sent as high and low signals as opposed phase signals at a baud rate of 500kbit/s to the instrument pack, in this data packet among others are the coolant temperature signal, the engine speed signal, and ambient temperature signal. This is fed into a multiplexer IC within the KMB, the very same device also interprets the information in and out from the DS2 Bus, Nav Bus, trailer bus, Window bus, in fact the KMB is the central processing area of all of the data busses. In the case of the CANBUS, the KMB decodes the data packet, and transmits data on the lower speed K-bus to whichever ECU is prioritised first, and the ambient temperature signal, previously transmitted from the ECM on the CANBUS, is sent to the HEVAC ECU transmitted on the K-Bus, and as there is not a valid signal transmitted forward from the HEVAC ECU onward to the BCU on the K-Bus, heated rear window operation is inhibited. The CANBUS is always treated as highest priority in terms of data transmission over all other data busses on the car, as it is where the critical safety decisions are made, but failure particular of one transmission line, in this case instrument pack 3, compromises only the recipients of that particular data line. The CANBUS Messages 1 is reserved for ABS operation and SRS operation, and Messages 2 relates to JATCO EATCU, I think I've already covered the operation of Messages 3 So can you appreciate now, why failure of the CANBUS controller in the ECM has the affect it does on the heater rear screen? It's a bit like the having a gap in a line of dominoes, if all of the brown "CANbus dominoes don't fall over, the white K-Bus dominoes that follow the brown ones don't either. Brian :getmecoat: |
WOW.---No wonder things cost lots of money with the manufacturers going out of their way to complicate things.
I would fit a switch in a wire from the battery to the heated rear screen and be done with it. Lol.-Cost about 9 pence. ( And would switch on when I wanted it to and not in that annoying car habit. ) |
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Regards |
Thanks Russ and Brian for your detailed and interesting explanations. I have two questions arising from them.
My research was based on my KV6 which, of course, uses a different ECM to Edward's M47R. Is there a different mode of operation at work here between the two? As I indicated earlier, the exterior temperature signal bound for the BCU doesn't go anywhere near a CAN bus on the KV6. I have to agree with Colvert that it is absurd, on the diesel at least, that the HRW cannot be operated manually in the absence of an exterior temperature signal. It's interesting that TOAF can apparantly disable this restriction. Can T4 do the same? Simon |
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There is no difference in the operation of the KV6, Diesel or 1.8 ECMs they all use the Can-bus to input the ambient air temperature to them. Quote:
The ambient air temperature signal goes to the IPK multiplexer IC where it's converted to Can-bus and K-bus signals. Consider it if you will as a connection. As we both explained above Can-bus messages always take priority so if ECM loses the Can-bus signal then the IPK multiplexer IC effectively blocks the ambient air temperature signal from being transmitted on the K-bus. Fortunately the Can-bus controller on the Siemens 2000 ECM seems to be more reliable, but the same symptoms can happen if the Can-bus wiring is damaged. On the Diesel models it's nearly always the Can-bus controller in the ECM that's failed. Quote:
TOAF probably recodes the BCU to ignore the ambient air temperature, they seem to have included some other stuff as well such as one shot up on all windows with no anti trap Ouch!!! ;) It would be interesting to see if this affected anything else on the vehicles systems. Russ |
:}:}Thanks for all the information!
My priority it’s to make all the car systems to work again, not only the HRW, I can live without it for now. I saw that when the weather is a bit warm, the gauges along with the aircon and HRW works intermittent, but when there are near 0 degrees, they won’t work. So, first thing I want to do is to check the cables to see if the signal it’s lost here. I need to check the wiring near the right headlight when you look from the front of the car, right? The one near fusebox. Second, if the wires are ok, I will change the ECU to the spare one to see how the car does. If this solves the problem, I will proceed to take the bad NEC from my main ECU and put the spare one here, or like Brian said, to change only the little 8 pin IR from the middle of the ECU. If all of this fails, the last option is to replace my ECU and I will contact Brian. But I think I will do this after the holidays, the weather isn’t good too for working on cars. Thanks for all the help guys, I learned a lot about the car and did many DIY jobs with information from this forum! My first car that I started to do DIY jobs, heh. :} |
Easiest way to check the wiring is to warm up the car first so it's got some heat that would normally show up on the guage then just plug in your spare ECU, switch the ignition on, if the temperature guage works and the HRW works then it's the ECU if it still doesn't it's the wiring ;)
If it is the ECU then I wouldn't attempt to swap the NEC chip you might just end up with two ECU'S that don't work, I'd do as Brian suggested ;) Russ |
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If we just think about that for a moment. Given that the IPK receives the analogue exterior temperature signal directly from the sensor then converts it into a K-bus message, and there is a clear route on a K-bus wire from IPK to BCU, then it is surely very bad design to disable this route simply because there's a blockage on another network (the CAN bus). To continue the bus analogy, it's like saying that the road is blocked between London and Nottingham so therefore no buses will leave London for Cardiff! That's insane. Quote:
Simon |
Russ. Could you tell me if the anti-trap on the windows works through a current sensing device ??
An abrupt stop of a window would see a sudden surge in current as the electrical path becomes almost a dead short. I like the way all the windows on my wife's Citroen can be closed from in the house if it starts to rain outside and I'm in my jammies.--:shocked: |
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