348 View inside the Climate Control ECU - Info Request

Does anyone have access to a 348 HVAC ECU and can look inside to verify a component for me? This is part number 151711, but the later version (black back, not white). Circled in white is the item that I need info on because I'm not sure if this one is original (and maybe not correct).

The one photo is a peek inside with the back cover removed. The other is with the board removed and separated from the other board.

Thanks.


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Here's my problem, for starters...


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It is (burnt) original. It is a resistor and should have "68RJ" written on it. On one of your pictures, it appears that the writing is still visible; can you read it?

If you confirm 68RJ, then it is 68 Ohm resistor of some 1-2 Watts. You can replace it with a standard resistor of the same Ohm value and similar size. However, it is possible that the resistor was overloaded and burnt by some other failed component, in which case the same will happen to the new resistor. After replacement of the resistor, connect the AC ECU briefly and, if it still does not work, disconnect it immediately. In that case, you will have to first check the power transistor next to the blown resistor.

 

Here's some close-ups:


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I looked everywhere for this and found that Bosco bought all of SECI's inventory when they closed.

http://www.boscoelettronica.com/en/industrial-electronics/power-resistors/

But I'm not sure if this is the original part since it's obvious that some repairs have occurred in the past.

Are you talking about replacing the Motorola part TIP 142 9144?

 

What about this little guy? The blue PTC? Looks like C995. All three items in the photo are in the same circuit for the temperature control valve - E5 error.


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It is a 0.82 Ohm resistor (it was nice green colour originally). So, look for a 0.82 Ohm resistor in radio shacks, at least 2W but better 5W since there is enough space to put in a bigger one. I suspect that the large transistor next to the blown resistor is controlling the heater pump (the highest load "consumer" for the AC ECU) so check whether your pump motor is good by connecting 12V directly to it. If the motor has failed (seized or has a short), it will probably not run but draw excessive current which could have been the reason for the resistor (and possibly the power transistor) overload ad damage. In fact, it is better to check the water pump motor first, then the large power transistor.

 

Okay, thanks. It seems like maybe the SECI resistor is not the original - appears to have been worked on in the past.

Previously, I checked the heater valve motor and the valve itself. Both seem okay. Tested the system with the motor detached from the heater valve... same thing, an E5.

Swapped in my old HVAC ECU (early 151711 with white back shell), had an E1 code on startup. But I noticed that, by moving the main cable a bit, the ECU would lose power. Wiggle the cable again and the E1 comes back.

Turns out, the yellow connector wasn't fully seated and locked in. Although it seemed that it was.

So I switch back to my original ECU, thinking the same (loose connector). Nope, still an E5. That's when I opened the box and found the cracked resistor.

BTW, everything works perfect with the old ECU except it still has an intermittent loss of power to it.

 

I wouldn't worry about the PTC, it looks good (never mid the chipped-off coating at the leg). I suggest that you, straight away get both, the resistor and the transistor. The transistor is TIP 142, easily available ("9144" does not count, just a batch number). This transistor is the same as the two power transistors inside the fan speed controller so it is good to have a few of these as spare. Once you have verified that the heater pump motor is good, install a new resistor and give the ECU a brief check, with the ECU connected but still out of the box (if possible?) and keep an eye (a finger) on the new resistor. If you see it gets very (burning) hot or starts smoking, disconnect the ECU and then go to the transistor.

 

It is original, I have one removed from my (now modified) AC ECU - same green colour as the longer resistor next to it. Your resistor is black because it was seriously burnt.

 

Interesting. Thanks. Do you have those part numbers.

Separately, I was surprised to see the huge difference between the early and later versions of 151711.

White back shell - made by AME (disregard the white circle):

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Black back shell - made by Magneti Marelli :


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If I remember well, the SECI R82 (0.82 Ohm) resistor that I removed from my White-Black ECU is the one marked by the red line on the pic below. Otherwise, there are no part numbers for the resistor or the transistor. They are just a "0.82 Ohm" resistor and a "TIP142" transistor.

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I had a look at the circuit board (same as the pic above) removed from my AC ECU as well as at the wiring diagram. I can confirm that the transistor TIP 142 and the resistor R82 (0.82 Ohm) are the power circuit that controls the Electric Water Pump, via the Pin 14 of the ECU's yellow socket (2nd pic below). The internal AC ECU circuit (the transistor, 1st pic below) connects the negative terminal of the pump motor to the ground (the motor has ignition switched +12 volt on its positive terminal) thus switching the pump motor on. The motor current flows through the resistor (R82) and then through the transistor (TIP 142) to the ground. The R82 resistor is there to somewhat limit the current and protect the transistor.

So, if the R82 resistor is burnt, it means that there was overload by the pump motor. The code E5 you are getting means "Motor for heater valve control" but it may not be accurate. In addition to the burnt resistor, such overload current might have also damaged the transistor TIP 142. The checks should start with the pump motor (sized or has internal shorts in its windings thus drawing excessive current). With regard to the transistor, if you don't have the means to check it, just replace it (or replace it anyway). And a new resistor, of course.

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SECI before....
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...and after.
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Related info:

A good water pump motor draws 0.5 Amp when not loaded by pumping of fluid. It probably draws about 1-1.5 Amps when in the coolant circuit (I have no easy way to check as my pump is no longer in my 348). So, if it draws considerably higher amps (say about 3 Amps) when tested while still in the coolant circuit, the motor is either seized (stalled) or just bad.

 

Great info, thanks Miroljub.

The later ECUs and their boards are quite different (the one I'm trying to fix). However, the R82 does lead to Pin 14 here as well (see red line in the photo).

I'll replace the R82 and the TIP142, but will check the water pump while waiting for pieces to come it.


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Also check the diode next to the resistor.

 

Close inspection it appears to be okay, and I don't think I can do a test without removing it from the board.


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Also, I see that this unit has been worked on before and I'm concerned that some parts may be incorrect.

For example, notice the legs on the TIP, which don't quite match up with what's on the board. Also notice that the white line is applied after the legs were soldered.

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You can probably test the diode in-situ when you also remove TIP142 as the anode of the diode appears to be connected only to the link from the SECI resistor to the collector of the transistor. If this is correct, you can test the diode on the pc board but I don't think there is any problem with it as it seems that it just conveys a small signal - the information on the voltage drop across the SECI resistor, to the small transistor near the diode. The small transistor is driving TIP142 (via its base) and the voltage drop monitoring should be a kind of overcurrent protection circuit for TIP142 - if the voltage drop across SECI is too large, it means too high current caused by the pump motor; the small transistor should then start reducing the current through TIP142 to prevent its overheating. However, it seems that in your case this did not help. There is probably a limit as to what overload current this circuit can compensate for. On the other hand, it is possible that the main culprit is actually failure of TIP142 which, if resulted in a short in it, left the water pump current flowing through the SECI resistor directly to the ground, thus resulting in the resistor burn-out. You will find out when you test the pump.

Otherwise, the solders of TIP142 do not really look as redone. I don't think any repairer would bother about the white line so it was probably drawn during manufacture.

 

Yes you can. Not for 100% but you are sure for 95% when it checks out ok.
As M already stated it is probably a protection diode for the TIP142 for reverse tension spikes coming from the waterpump. If the diode is SC the current will burn out the resistor. So do check the TIP and diode both.
And of course wiring and pump.

PS :Those solder joints look really bad.

Grts
Patrick

 

Great to know about the diode, so I may skip testing it. Notice the one end is connected to the board's surface trace, same as a resistor. Unfortunately, it's impossible to see what's connected to what under these three components.


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Regarding the TIP, the soldering on the board is pristine (both sides), but maybe its legs were snipped during a previous replacement?


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The legs may not have been cut, they have steps near the transistor body:

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