r1de23

have fun with an electrical problem... not my realm..

archimense

If VAG-COM cannot communicate with the ECU, then the ecu is dead or doesn't have power.

You can remove the ECU completely from the car and you will have the same symptoms as you have now.

s4TTq

thanks for all the replies guys, wanted to follow up...

i knew that the missing CEL and EPC had to be related directly to the ECU, so lack of power to engine module, bad fuses, bad relay, or bad ECU.

Multimeters are great, and heres why:

-battery terminals reading 12.44Vs (or you could use cluster gauge)
-In car terminals reading about 12Vs
-Hooked up relays to 12V power source and multimeter to appropriate terminals, and have multimeter test connectivity.

All tests came out good, so it had to be a bad ECU. borrowed an M box from my mechanic (even though I have a 2000) and unplugged the MAF. I started it up and let it idle for a while, then gave it a little throttle to test that fueling system where all in order.

So yea, bad ECU. but for guys who search the forum in the future, this is the proper way to test.

Klum00

So, I'm coming up with the same problem but mine is sporadic. Most of the time the EPC light comes on and the car starts fine. Then it will die at some point either while driving or while idling. Sometimes it will start right back up and sometimes the EPC light won't come on in the ignition position and the car wll crank forever but won't start.

I've checked the grounds behind the coolant resevoir and have replaced the engine speed sensor which seems to be a culprit sometimes. I removed my GIAC chipped M-box ECU to see if I could see any problems. Didn't seem to see any broken solder spots and the harness seemed to be fine.

Any suggestions? I'm going to try and throw one of my Tech's ECU's in to see if that remedies the solution, but since the problem only happens sometimes I'm doubting that the ECU is the issue.

donromani

yeh, that sounds more like a bad connection somewhere. At the very least your ECU is not completely Kaput yet or you would never be able to start it up.

timmy2tyme

the past week my 01 s4 has not been turning over it only does after i let the car cool down completly then it will turn right over no problem it happened alot latly but only when i shut it off andturn itback on right away

any waY IM PREETY SURE its the fuel pump relay or somthing related to that
their two pumps one from the tank and one to the motor so check the fuel filter if its clogged it might not turn on .

let me kno if yourstill having that problen cuz it sounds simialer to mine?

donromani

The engine does not turn over at all when hot? If it's not doing anything at all, no mechanical noise whatsoever, then you might have a bad starter.

sincitys4

I know this is an old post, but what did you find out that was wrong with your car. I'm having the same problem with mines right now.

nimmote

I havent had that issue with the S4, but my B5 Passat with the same 2.8L V6 has had an issue starting a couple times where it would crank forever even when i tried jumpstarting it with another vehicle and it would turn over once or twice but wouldnt keep running. I would smell fuel, I then read that it was a common issue if the car only ran for a few seconds (like to just move it out of the way)it would flood the engine and then you tried to start it later in the cold weather with no luck. The fix for that was to just hold the pedal to the floor and crank away and holding the pedal to the floor would keep more fuel from getting into the cylinders and fix the flooded engine problem. I have had that twice now. I had to crank for like 20 seconds straight, give it a few minutes break and then crank again and then it ran. That might not be your issue, but i wanted to share just incase it helps.

MonroeS4

Strange that no one questioned the Immobilizer? 2000.5 S4's have them. Glad I read this thread I was not familiar with the CEL/ESP lights being of importance to note for a no start problem. Learn something everyday. Has this issue been resolved? The fix was?