C3 Earthing problem runs with obd2 scanner attached

[ozvtr]

Well I have no idea how the scanner is getting the engine ECU to start when the ABS ECU is disconnected AND I have no idea why the engine dies when the scanner is removed! The only communication lines to the engine ECU are the CAN lines and they are severed when the ABS ECU is disconnected! The only thing I can postulate is that removing the scanner stuffs' up the CAN BUS and the BSM "drops out" cutting power to the engine ECU?
Meannamate, is there anything else that doesn't/does work when the scanner is/isn't plugged in?

The circuit diagram doesn't even show the CAN line connections at the OBD2 connector (C001). I don't know what pins 3 and 8 are doing but It's not part of the OBD2 standard.

I would do continuities between pins 19 and 21 and 23 and 25 with the electrical connector disconnected from the ABS module. Check for open circuits of those pins at the plug on the loom. If they are open circuit, bridge them as wheeler says. Start and run the engine with and without the scanner connected and the pins in the connector bridged and not bridged. I would try all possible permutations to try and get a clearer picture of what's going on...if that's possible.

Unless it's just the way they have drawn the circuit, there are no other ECUs on that CAN BUS?

[Meannamate]

Ok! This is getting juicy! All ECUs connected. ABS disconnected. Scanner disconnected. OL at pins 19, 21, 23 and 25 (that’s assuming I’ve read the pins correctly- on the plug only pin 12 and 26 are numbered, so I went for the pins between). Is the there a plug pinout anywhere I can check? I’ll post a numbered pic. Anyway… with the pins bridged it doesn’t start. Am I missing something?

[wheeler]

I think you may have the pin assignment wrong on the left hand row. You have also written 12 twice? Looks like bottom left pin is 13 14 & the top left is 26.
If you take the back cover off the plug you should be able to check the wire codes tie pin with the pin numbers. You should also be able to easily identify the CAN wiring as they will be in twisted pairs.
If you dont have 120 ohms across each of the pins i said above then bridging the connector wont work anyway.
If you re post the connector picture again without marking it up i can highlight where I believe the pins should be.

[Meannamate]

Hi wheeler, apologies. Bottom left looks like 16. Difficult to see but would be correct if top left is 26. If top left is 26 then I think the bridging was correct. Here’s a clean pic anyway. I’ve removed some insulation at the back of the plug and can see the twisted wire pairs. I’ll dismantle the plug and retest.

[wheeler]

This is how I reckon the should be. Ran out of time to do one for bridging but will do it later. Need to know there is 120 ohms on each of these wire pairs first before bridging anything.

[wheeler]

This is what I reckon should be bridged. Need to make sure you have both your 120 ohms first.

[ozvtr]

[Meannamate]

Progress! Ok, so after your lesson on how to count and particularly how to count pins… I read 120 ohms across 25-23 and 21-19!! Hurrah! I then bridged them and hey presto car starts immediately! With the expected ABS warning light and ‘braking system faulty’ message. One thing I noticed was that when reading the resistance it crept up slowly from about 40-60 up to 120. Is that significant? Where do we go from here?

[wheeler]

Progress indeed, the fact you are getting 120 ohms on each of them suggests the CAN wiring is OK.
Not sure about the progressive creeping up reading, not something i’ve came accross.
Also you have removed the ABS ECU from the network & its now starting ok. That suggests to me the ABS unit is the problem. It would definitely be worth reconnecting it all back up just to confirm the fault returns again.
Also be careful sticking paper clips in the terminals, its can stretch them out & cause bad connections.

[Meannamate]

Ok, I went out during my lunch break and reconnected the ABS. Tried a few times to start it. It will start intermittently now. Then the dash faults come back after a few minutes running. Left it to run and took the key out. Engine carried on running as before. So to stop the engine I plugged the scanner in. Restart with scanner connected and no faults as before.

From this then I’m guessing it’s the ABS unit (or could it be an associated relay?). If it is the ABS, am I right that a new unit has to be recalibrated with Lexia et. al.?

(p.s. they weren’t paper clips, I tried to use bits of wire as close to the pin thickness to avoid stressing the connectors)

[wheeler]

A new unit is over £700 so i'm guessing your looking at used parts? A second hand unit can be used from another car no problem, If the spec of that car is different it may need some options changing. There are only a few things that need setting, Tyre size, gearbox type & something else i can never remember. You need to make sure you get a unit from another full CAN model so try get same year.

[Meannamate]

Brilliant thanks! I’ll start trawling for a replacement. I guess there’s nothing can be done with the old one?
I’ll report back on any progress… Thank you again, wheeler and ozvtr! I couldn’t have got anywhere near this far without your help!

[ozvtr]

One thing I noticed was that when reading the resistance it crept up slowly from about 40-60 up to 120. Is that significant?

No. Capacitance in the line. Probably part of a filter.

[ozvtr]

Yep. Scanner just enough to keep the impedance acceptable and CAN BUS running. Engine ECU would have to be connected to CAN BUS for engine to start. Also BSM may not apply power to stuff at key on with the CAN BUS not running. When engine is running and ECU gets disconnected from the network, engine light comes on but engine still runs. BSM seems to lock up too. Doesn't cut the power to the engine ECU when the ignition is turned off. Plugging in scanner balances CAN BUS, BSM starts responding and cuts power to engine ECU.

I don't know if you know it but you can remove the ECU from the hydraulic block and not disturb the brake lines.
Is the ABS actually working? The BSI is receiving an 'acknowledge' from the ABS on startup (no ABS light). So you can assume the hydraulic pump is working? Salt water can get inside the motor and corrode the motor and the electrical contacts. In which case you would want to replace the whole block. But during the ABS POST, it runs the pump to check the circuit. If you don't get an ABS error I guess you could say everything else is OK and you just need to replace the ECU?
HERE is a video. Not the same module but you get the idea.

I am a little perplexed as to why the ABS ECU is a "pass through" for the engine ECU. Why isn't the ABS ECU just paralleled off like the other ECU's? If the electrical connector pins and sockets are serviceable, what's in the ABS ECU that's "broken"? Logically there are just tracks on the ABS ECU's circuit board bridging the 4 pins? Or is there something inside the ABS ECU that's gone faulty? What? Why? Are you sure pins 21 and 23 in both the ECU and connector are serviceable? It could be the solder joints where the connector pins are soldered onto the circuit board inside the module. But you need to be sure its the module and not the connector.

[wheeler]

Early C3's were really bad for water ingress into the ABS unit due to where it is located, so much so that they were recalled to have mods done to stop it. One of them was to inject electrical grease into the connector, you will notice all the grease in the pictures, this is done at the factory now.
Yes the £700 i mentioned above was just for the Electrical ECU, if you wanted the full hydraulic block thats over £970
I would imagine most breakers would only sell the complete unit but its only a couple of screws to separate them.
Would be interesting top open up the ECU to see if there is anything obvious wrong with it.