Technical 2004 Punto HGT wont start cannot connect to ECU via OBD2

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Technical 2004 Punto HGT wont start cannot connect to ECU via OBD2

SLAM3R

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Joined
Dec 13, 2021
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3
Location
Auckland
Long one sorry, trying to get all the relevant info in the first post.

I recently purchased a 2004 Punto Abarth 1.8 HGT (which had been parked for my first 3 months of ownership due to lockdown till last weekend). We took it to a trackday and t was driving fine but then the check-engine light came on. No noticeable issues, stopped it and checked over what we could at the time found nothing obvious so kept driving it the rest of the afternoon (intending to look into it the next morning) then parked it at home overnight. The next day it would not start. Cranks over, and after some testing can confirm it is getting fuel pressure but no spark. Grabbed an OBD2 dongle (3x different ones actually) and installed several OBD reader apps on my Android phone, and after a lot of trial and error we eventually got some results from "AlphaOBD demo", where it connected to the ECU and it reported P0340 Phase Sensor (Camshaft position sensor), and U1601 CAN line error.

Seems logical that the cam position sensor is the most likely cause of the 'crank but no start' issue, however things have gotten a little more frustrating. We can no longer communicate with the ECU, it's like the ECU is dead/missing. We have tried all 3x OBD dongles (one bluetooth, one wifi, and one KKL USB cable via a laptop running MultiECUScan). We have intermittently been able to use each of the dongles with success initially (it was often flakey and dropping connection to the ECU before), but now nothing will connect to the ECU at all, spent several hours trying different dongles/apps/cellphones/laptops with no luck. Note, the app will connect to the OBD dongle fine and stay connected, just cant connect to the ECU.

We've checked every plug and ground connection that we could find and they all look perfect (no signs of damage/oxidation on any connectors/etc). Battery is fully charged. All fuses have been checked and are OK. Removed the ECU in case we could open it up and look for signs of a failed component but it's sealed up tight so gave up on that and put it back.

The dash still 'looks' normal, the CODE, ABS and other preflight check lights are coming on then turning off after key on for few seconds like normal, it still cranks but wont start, so I guess the ECU is still doing something, we just cant seem to talk to it any more.

If we were 100% confident that replacing the camshaft sensor would fix the car we would probably just do it (is this an engine out job as it's behind the timing gear which is basically wedged up against the engine bay/frame rail??). But since we cant talk to the ECU any more, I'm wondering if there is another, more sinister, electrical issue. I don't really want to pull the engine out to fix the sensor to find that the ECU/wiring is faulty and the car still wont run.

I have seen before where a CAN error on an unrelated module/wire can interfere with CAN communications to the ECU, so I assume this is a possible cause here. Any thoughts on things to disconnect in order to diagnose this better?

I am in New Zealand and these cars are not very common here and there are very few mechanics/workshops that work on them, let alone know them well. My friend and I are competent hobbyist mechanics (work on 90s era Honda's normally, this Euro thing is new to us.)

Also, we back-probed the camshaft position sensor connector with a multimeter, and when not cranking the voltage from the signal wire (middle?) was 5.8V, and when cranking it went to 6.0V (I might have those numbers reversed, I cant remember which way round it was) so this would indicate the sensor is doing 'something' and the wires to the senor are likely not broken, but I'm not sure what the correct voltages should be.

Anyway, sorry again for the long post, if anyone has any suggestions let me know. :D

Thanks
Matthew
 
Joined
Jan 11, 2015
Messages
2,101
Location
Helsinki
The connection from the ECU to the OBD port goes via the small connectors nearest the battery which are under the fusebox cover. Depending upon which ECU you have there is a very good wiring diagram available for the ECU's in the punto downloads.
 
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