Hello,
Im new to b5s and really any car newer than a mk2, and absolutely hate auto electrical systems. Im a novice when it comes to working on cars, but i have all your basic auto repair tools and know how to use them but, but admittedly suck at diagnostics.

The problem:
Turn the key in ignition engine cranks hard wont turn over, all lights light up then shut off as they should besides the battery light which as expected lights up after cranking for some time, as well the fuel light stays on unless im on the gas.
Check engine light never comes on.

Diagnostics:
Cracked the fuel line going into the front of the fuel rail and only got gas to trickle out, no pressure when turning key.
No spark.
Battery is showing 10v on its own, and over 13 when jumped to a running car. i would believe its low volts is from hard cranking and not my root problem.
OBD reader isnt giving me any readings or codes.
I have a cheapo blue tooth obd reader that works with an app on my phone, i have gotten a few readings and codes off of it before so i know it works. before it would show me real time data, which now it only tells me "no data" for every reading. Leading me to believe that the ecu isnt communicating.
replaced the ecu with another used unit and it has made no difference.

The car:
99.5 aeb
all stock
151k miles
tiptronic
car had no issues in the past couple of months.
recently changed oil, filter and tranny fluid.
over winter it had a hard cranking problem, but i was lead to believe it was weather related and didnt worry about it.
car ran perfect and got me too and from work the night before not starting

all this leads me to believe that the ecu isnt getting power or signal from key?
if its any help i can try to get some video later

please help me solve my problem and please dont tell me to send it to a mechanic, family is really tight on money and need this car running asap.

pic for attention:

i know, needs suspension and tires, all ive been able to do so far is get wheels

 

When you turn the car to the on position (prior to cranking) does the CEL turn on? If it doesn't, make sure the CEL bulb isn't burned out. If your CEL never turns on or flashes you have an ECU problem.

You say the fuel light is on, does the car actually have gas to start?

Again, check your fuel level. A more proper test would be to pull the fuel rail and injectors and check that they are firing. Alternatively, if you have been cranking the car and it's not starting, pull the spark plug and check the piston to see if it is wet.

How did you determine this? A spark is a necessary condition for an engine starting/running.

That could very well be…I would attach a trickle charger to keep the battery charged before attempting to start it again. 10v isn't going to get you there.

I don't trust your bluetooth OBD reader and app to pull all the codes from the ECU. Buy a blue $7 VCDS cable from ebay and download VCDS Lite to scan for codes. This is an absolutely necessary and basic diagnostic tool for these cars.

The car needs three things to start. Compression, air/fuel, and spark. You need to make sure the car has all three and that all sensors are working. If your cam position or crank position sensor took a dump, the car won't fire up either.

With all due respect, if your car needs suspension work and new tires, new wheels doesn't seem like the wisest of purchases..

 

thank you for your response, but i need help diagnosing why the ecu isnt working properly

 

Yes, you could remove the cluster to check the bulb. Pull the trim piece forward and there are two torx screws. You shouldn't need to unplug the other connectors to get at the CEL.

I didn't realize you were using another car to jump it. I meant use a trickle charger to keep it charged overnight while you figure this out.

The fact that your reader pulled codes off a Hyundai does not mean it is pulling all the codes off the Audi, what brand and model reader is it? The $7 that the proper cable costs to use VCDS Lite (which is free) is worth the money, trust me on this.

I am not familiar enough with the cam and crank sensor circuits to say that they would cause your exact symptoms, but I do know that if one of those sensors is bad the car won't start.

The fact that you replaced the ECU with another one already and it made no difference is not a good sign. You're sure the spare ECU is a good one?

 

The ECU on my 99.5 A4 went out at about 145K miles. This doesn't mean that is your problem, but it's the first thing that popped in my mind reading through your write-up. I have the same problem, good crank, no start, no connection with reader, and the CEL never came on.

The easiest way to troubleshoot this would be to find another ECU with the same part number (557 P if memory serves me) and swap it. If you know anyone else near you with an AEB engine, you could swap it out and see if it'll start. Then, find a used one for under a hundred bucks. I found my replacement at a salvage yard. Good luck.

 

the code reader has pulled codes from the a4 as well as other live data like coolant temp, voltage, throttle position and other readings. all those readings show "no data" now, the lights do light up on the unit though, so there is at least power at the port.

i dont know for sure the 2nd ecu does work, i could have been sold junk.
i got advice on another page on what pins to check for power to the ecu, after i check that if all is getting power like it should ill try another ecu

 

I would look at the fuses. At least One of the wires at the obd port is supposed to have power all the time, without a schematic in front of me I'm not sure which ones. I do believe there is also a DME relay. Do you hear the fuel pump run at all? It should run while cranking and then for about 2 seconds after (with key left on).

 

Sorry for my ignorance, but is the fuel pump activated by the ecu or no? I don't think i'm hearing it but that doesn't explain no spark, hence why I'm focused on the ecu.

All fuses checked out okay.
How do u cheek relays? Find a relay diagram and test them by putting hot and ground to different teeth and listening for it to open/close?

 

Sorry, I missed the part about you said you swapped the ECU already. You may be correct that it was a junk part (I've had it happen before), but I don't know.

 

First things first; make sure the CEL light is operational and that it comes on. We can move forward from there.