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The ignition circuit stays live even after the ignition is switched off and keys removed. Doesn't go off till either battery disconnected or if you switch on an aux power (wipers etc) to consume the voltage.
i've tried this ecu on 2 separate cars and both do the same thing
Decided to have a play and see if I can't figure this out.
Found damage on the back of the circuit board going from B136-32 (self shut off control). Traced the circuit board and found it goes to a component on the board but unsure what it is? Tested across it with a multimeter and the other components that look the same as it and found the one on the self shutoff circuit appears to have an open circuit.
Can anyone tell me what it would be or where I might be able to get one?
It's a diode, so it should read open circuit in one direction, but read a resistance in the other direction, so it would be worth double checking it before searching for one I would say.
To check the opposite direction you just need swop your meter probes around so if you had your red probe on the left and black on the right swop them so you have black on the left and red on the right, although in an ideal world you would check it out of circuit i.e desolder it first. But checking it situ will give you a general idea. If it is suspect desolder it and recheck.
Brilliant thanks for that, I'll recheck it tonight then in both directions. As said I tested the others that look the same next to it and got readings so never thought of it being a one way diode.
Thanks again
After realising it's a one way diode I measured the diode the other way (switched my probes) and found it's giving a good reading so sort of back to drawing board again
Rechecked the circuit again and found there's another diode in the circuit, D33.
Measured the diode both ways and getting 0 Ohms both ways. Guessing that means it's burnt out?
Also carried out a diode test with my multimeter.
On D29, D30 and D31, one way I'm getting 0.5v and open circuit the other way.
On D33 I'm getting 0v through the diode both ways too?
On appearance they all look the same so should surely get the same?
Correct. Sometimes while in circuit they can read a resistance both ways which can be slightly misleading. In that scenario you would need to remove it from the circuit and recheck it to be certain it was dead short.
In your case you've got it easy as they should never be open circuit both ways whether they are in circuit or not. So you're on the right track as you definitely have a duff one there.
Btw the units you're measuring are ohms not volts just making sure you're on the resistance or dedicated diode check scale on you're meter.
When I put my multimeter on the diode test it outputs a voltage to give a voltage drop which is why I was saying 0.5v across 3 of the diodes but getting nothing through the other...well that's what the multimeter said anyway lol.
Now I need to know what diode I need to replace this?
Ah I'm with you now, all good then. Get all the numbers off it and try a google search with a heading of "smd " (surface mount diode) and you should get some decent results. It will be something along the lines of a high speed general purpose. I can make out what looks like jc marked on it on your photo which could possibly identify it as Phillips brand, but the other numbers will be the deciding factors.
Try Farnell or Rs etc.
Hi
Looks like it is on the pin connection so at the input stage.
Its probably a revers polarity protection diode so basic rectifier diode.
Hard to identify it from the pictures but I could make some estimates. http://uk.rs-online.com/web/p/rectif...iodes/8231625/
I would measure the physical package and identify what is connected to the pin.
make an estimate of the current at the pin, I would assume looking at the tack <5A.
Also safe bet that it is <24V, automotive uses this to protect for dummies jumping to a truck, but as there may be surge voltages if the load is inductive I would fit a 50V part.
If you can identify the load at the pin you can fit a diode to match, add 50% for the current rating or you will be back quickly!
RSwww.com has a component selector that includes size so you also need to measure the physical component.
Then you need a good soldering iron and steady hand!
better still find someone that can do a SMD repair for you, they will probably have a stock of SMD parts as common in power supplies.
Dave
Thanks Dave, really appreciate that. I was hoping to find someone who's got more experience on ecu's and electronics as this is a little beyond me after the vehicle wiring lol and then as you say they'd stick the right replacement diode.
I'll see about measuring the diode if I can to see if it helps at all
Hi
As an electronic engineer if it was my car I would be tempted to do the following:
Identify if that diode is direct to the output pin, easy enough to measure with a meter.
If it is remove the diode and just add a rectifier diode as big as I can fit, 30-50V 5-10A.
Check what caused it to fail before re-connection.
These parts are normally very strong so failure could be external to ECU causing excessive current draw.
Down stream is probably a switch (MOSFET transistor) that switches from the micro to ground. If the diode is toast then there is a good chance this has also been compromised.
Normally when these fail its not so hard to see as they pop the covers to let the smoke out (all electronics being based on smoke technologies).
Transistor is not more complicated to replace if you find someone with SMD (Surface mounted device) tools.
Donīt try this unless you know what your doing, you will probably over head the board and lift copper tracks. The the right tool is a 15 min job.
Dave
I found what had caused the fault, someone had dented the ecu case so that it touched on the circuit board and it had fried the circuit track for the self shut off control. They'd then soldered a piece of wire to replace the track and put insulation tape over the top (I found all this after opening up the ecu).
After checking the repair found the wire had been poorly soldered so removed it completely and bought some electric paint which had been recommended to me to repaint the track onto the board.
During inspection of this circuit though I thought I'd check the diodes and found there's 2 in the circuit. The first one in the circuit (D33) is the one that appears to be fried after carrying out a diode test, and the one further along the board (D30) appears ok.
Forgive my stupidity, but how can I test the diode then to see it's rating using a meter?
Really appreciate your help thanks.
03 July 2017, 07:36 PM
Correct. Sometimes while in circuit they can read a resistance both ways which can be slightly misleading. In that scenario you would need to remove it from the circuit and recheck it to be certain it was dead short. 
(all electronics being based on smoke technologies).