Car will not start J271 relay issue with a curve ball!

[runvsofme07]

Ok, so my car is sometimey it will start fine for a week then throw a code but no light for Intermittent power failure. I can then disconnect the battery let the car sit and it will start again MOST times. Heres where it gets tricky, im looking up the part number for the ecm relay (#30) and the one that is in my car is 165 906 381 with a mfg date of 6/97. clearly it has been swapped out at some point because my car is a 2000. Anyways when i look up that part # i can find it for pretty cheap but its not the original relay it looks like it came from a vw. I didnt have any problems with it until my car got chipped. Is 4D0 951 253 the correct relay? Or are they the same thing?

[Mad Cow]

Where did you get 4D0 951 253 from? The correct relay is 165 906 381, but it usually isn't the issue. When you get the no start condition, does the CEL turn on with all the other warning lights?

[runvsofme07]

Im pretty sure the check engine light turns on, the car is starting and running for the moment. I just ordered a 165 906 381 since it was fairly cheap. There are only two relays in the box, i couldnt figure out which one was the ecm relay but i now know that 4d0 951 253 is a 4 pin relay not for ecu.. but i checked the grounds and they looked ok, and the wiring looked good. The 40 amp fuse in the box was blown so i replaced that but it didnt solve the problem.

[Mad Cow]

The DME relay is the black one, behind the other relay. If the CEL comes on then it's most likely not the relay because that means the DME is getting power, and that fuse is for SAI so yea it's unrelated. Next time this happens watch for the CEL to be sure though, or alternatively connect vagcom before you try starting and see if the communication interrupts at any point.

[runvsofme07]

I did that Wed. night when it wasn't starting to see if I could clear the code and make it start, the vag com communicated the whole time, I plugged it up and went to measuring blocks and no issues occurred with the connection.. I should be looking for the cel to stay on while the key is in the on position? then it should go off during cranking right?

[Mad Cow]

If you had no connection issues and the motor still wouldn't start then it's definitely not the relay. All it does is turn the ECU on, if it turns on and stays on then it's doing its job properly.

[runvsofme07]

codes are 17925 and 18010, main relay electrical malfuntion and power supply at terminal 30 voltage too low, the 18010 is probably from disconnecting and connecting the battery multiple times. both codes are intermittent.. im going to get the relay now its only $13, what else should I be looking for?