1.4 petrol AUA No Start / Intermittent ecm/ecu comms problem

mk1BDA

New Member
Hi everyone, this is my fist post on this forum. Sorry for not posting an introduction as yet but I have a major problem with my A2 and i'm hoping someone may be able to help.

A couple of weeks back I started the car and after idling for a few seconds its started to run really rough (like it wasn't firing on all cylinders). It revved freely and sounded OK above 1200 rpm, but at idle the poor running returned and it would stall. I restarted and the same thing happened, ran rough and died, then I haven't been able to get it to start since.

The engine will crank, but it will not catch / fire up. The starter just turns the car over. It will not start with easy start either.

I've replaced:

Coil Pack
Spark plugs
HT Leads
Coolant temp sensor

Checks:

Check and clean of all earth points
Battery is fully charged
Fuel pump primes system with ignition
New fuel has been added and fuel appears to be getting through
Good compression
Inspect TB and clean. TB actuator internals appear contamination free and in good condition.
EGR valve looks dirty and old.

Diagnostic tool reading is intermittent. Switching the ignition on, I notice that the EML light is very quick to turn off. In this scenario, where the EML lights and almost instantly disappears (before ABS light for example). I am unable to make a talk to the vehicle ECU.

Occasionally, the EML will appear and stay lit if I leave the ignition on for a period of time only then can I talk to the ECU and I have been able to pull codes relating to the Throttle Actuator and EGR Valve. These codes are

p0638 Throttle Actuator Control Range/Performance B1
p0403 Exhaust Gas Recirculation Circuit Malfunction

The throttle butterfly is unresponsive, does not move or appear to get power or commands with ignition or throttle input. I believe the throttle butterfly should cycle / self check with ignition but could be wrong?

The EGR appears to click with ignition. I have noticed that, the EML light appears and disappears as soon as the EGR clicks (1-2 secs after turning key to ign on). In this scenario, as I mention above i have no ECM comms, although I can run a scan, it just reports modules such as ABS and Instrument panel cant talk to the ECM (P01314 for example).

Is there an electrical relationship between the TB and EGR that would prevent communication with the ECU?
If I unplug the EGR, the EML disappears altogether does not light up at all during ignition cycle. Disconnecting the TB makes no difference.

I find it really unusual that disconnecting the EGR results in no EML illumination at all. Having it connected, always gives the EML light (albeit for 1-2 secs) but there appears to be a problem either here or with the throttle that is somehow shorting out the ECU resulting in a no comms situation.

If anyone has any ideas what I am looking at here, or could provide a circuit diagram for these elements that would be much appreciated.
 
Hello,

Someone who knows the petrol engine better will be along to help soon enough.

Sounds like a fuel issue or position sensors.

I am used to the TDI engine however I have made a low cost check list below in no particular order.

1 . Fuse blown by faulty crank case breather hose heating element?
  1. Fuel pressure from fuel pump - Fuse?,
  2. Injector/s not firing - see number 1
  3. Injector loom damage?
  4. Vac hose worn through from fuel rail (left hand side) to sensor on side of engine
  5. Crank position sensor
  6. Cam position sensor
  7. Blocked crank case breather
  8. Blocked fuel filter
  9. Clear all your fault codes and attempt one fix at a time then rescan and so on, slow and steady.

I did read your post twice but I may have repeated something you already mentioned.?

All the best,

Andy
 
Codes could be a result of attempts to start with unplugged components

When cranking does rev counter indicate crank rpm
 
When I am able to connect diagnostics in live data I can see engine speed rpm when cranking do I have ruled out crank and cam sensors.

I have cleared all codes when I am able to connect. Switched off and then retried the ignition cycle and the 2 above codes return.

Is there any reason why unplugging egr would prevent the EML showing up and when I have EGR pluggged in EML shows, egr clicks and then EML disappears in about 1-2 seconds
 
Hello,
The throttle body will need to be reset. Did you do this?
Cheers
Andy
 
Hello,
The throttle body will need to be reset. Did you do this?
Cheers
Andy

Yes when I gained access to the ecu, i went to the throttle and performed a reset on channel 60. Although, it registered as successful there was no movement from the throttle at all during this process
 
this sounds very much like an ECU failing

exactly what I was thinking, I've opened up the secret compartment and everything is bone dry. I've sprayed some contact cleaner on the ecu connectors but to no avail.

I was initially searching for a relay or fuse that would control the ECU but im lead to believe there isnt anything like that on this model.
 
hello,
You could try eBay for an ECU, clock, barrel, door lock and keys package?
Couple on hundred quid on there. You could place a wanted add in the market place?
All the best and good luck
 
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