4 pin coil pack wire functions

[grillhands]

Ok, just a quick update. I rebuilt my engine and now my car doesn't start. I have the p0685 ecm/pcm open circuit. I replaced j271 and fuel pump relay. Fuse 29 appears to be good and i replaced it anyway.

I was checking the CP wires and i found that with the car on, none of the wires have power. Also, when i checked if they are grounded with the car on, Pin 1 was barely lit up, Pin 2 was lit, Pin 3 had nothing and Pin 4 was lit. I've read that Pin 1 should have power with the car on but i'm not seeing that. However, it lights up when i put positive to it almost acting like a weak ground. I'm using a typical test light to check because i'm frustrated and running out of cheap options. I have no clue how it got like this and it's driving me nuts.

Audicrazy said i should be seeing the volts of the battery on pin 1 but instead it acts like a ground because it faintly lights up when i put power to it.

[walky_talky20]

Indeed, Pin 1 is the power supply to each coil pack. The red/green wire. You are going down the right path here. Let me explain:

Your code (ECM Power Relay Circuit Malfunction) can only be tripped 1 way. It makes more sense if you understand the circuit. The ECM power relay takes constant battery power and uses it to energize only 2 fuses: Fuse 29 and Fuse 204. Fuse 204 is just for the cam chain adjuster and isn't really necessary for engine start. Fuse 29 is important, however. It supplies power to 5 devices: 4 coil packs and the ECU. The ECU actually has several power sources. This wire from fuse 29 is how it is able to "monitor" the relay circuit and it sets a fault if that circuit is not energized.

On the control side of that relay (the relay "coil"), 1 side gets constant battery voltage. The other side is simply a ground signal from the ECU. So the ECU is commanding that relay to close in order to provide power to the coil packs on Pin 1. And it is able to see if the relay actually closed or not, via fuse 29.

So the only way that code will set is if Fuse 29 is not being energized. That should be the first thing to check: check for power at Fuse 29. Use your test light. I can't say for sure that it should be on constantly with the key on (it probably should), but it should certainly be on whilst cranking the starter. If you aren't getting power there, you just keep tracing it back until you find the problem. The next device upstream would be the ECM power relay (as discussed above). You want to see if it is getting constant battery power on 2 of the pins. There should be a ground signal from the ECU on another pin, and of course the output to fuse 29 and 204 is the other pin. See what you get. I would NOT advise jumping past that relay to make it run. Damage can occur to the coil packs if their power supply is not under ECU control, or so I've heard. Never felt like trying it out.

As for their being an apparent "ground" on Pin 1 of the coil pack connectors, that is expected if the power is not applied to that circuit. It is because each of the other coil packs which are still plugged in (as well as the cam chain adjuster solenoid) is a load which creates a path to ground. If you were to unplug all 4 coil pack connectors as well as the cam chain adjuster, then you should no longer see that path to ground. If you do, that would be a short circuit which you would need to rectify.

Hope some of that helps. If you are trying to solve this yourself, you should really get a good electrical wiring diagram for the systems you are working on. Without it you are flying blind. And throwing parts at it is no fun unless you get lucky.

[grillhands]

Thanks alot for your help. It seems you are the only one who replies to my thread lol. This is far from the typical, " What exhaust should i get?" thread. I'm off Wed and Thurs so i'm going to play around with it a little more. I'm at the point where i need a battery now so i'm going to do that as well. I've seen a hanes manual at pepboys and i'm probably going to pick that up too. Once again, thanks. I've found this info:

The coil pack connections:
Pin 1: Connects to Pin 1 on all other coils and then to +12v ignition feed (or fuel pump relay).
Pin 2: Signal ground
Pin 3: Spark Signal from ECU
Pin 4: Power ground (Engine Earth)

[murdered APR a4]

walky is wayyy to smart for me lols

[walky_talky20]

Just trying to help where I can. I'd be useless at suggesting an aftermarket exhaust, haha.

OP: If you need a good diagram, just PM me with you email address and I can send you whatever you need. I've got Bentley diagrams which are horrible and will kill your brain, or I've got good aftermarket diagrams in color which are much easier to read.

[grillhands]

http://www.audigeeks.com/images/tech...tronic_ATW.jpg

I've found this. It's for a atw passat that doesnt have the icm like my car however i think it only has 3 pins coming off the CP unless the sparkplug counts as one. I'm not sure.

[grillhands]

Update. I do not have power to fuse 29 however when i took the relay out of the secondary air pump and put it in j271 i got power to pin 1 in the injectors and to fuse 29. The only thing is that's not the relay that should be in that place. I tried the old and new j271 relay and neither of them can give power to the injectors. I do not have power going to fuse 34 which is also a control ecu unit because i don't have my secondary air pump, maf, or n75 anymore. I didn't get a chance to start the car because it started to pour outside and i need a new battery. I checked the fuel pump fuse and it will get power for about a second then go back to no power with the key turned to on. I had a old LED test light that lights up green for ground and red for + that i've been using to get these readings. I'm concerned about trying to start it because it's not the right relay and i don 't want to mess anything up further.

[walky_talky20]

That is normal for the fuel pump fuse. It will "prime" for about 2 seconds when you turn the key from OFF to ON each and every time. It will give constant power to the fuel pump when cranking the starter, obviously.

I don't know the difference between those relays, but there isn't anything special about them. I believe both are just normal 4 pin relays. You should just make sure the pin-outs are the same, they usually have a diagram with the pin numbers right on the relay housing. If the power to fuse 29 is turning on and off correctly (with the key) it should be fine to try and start it. If it is not shutting off with the key, that would be the only cause for concern.

I'll try and get you that diagram this evening when I get home.

[grillhands]

That is normal for the fuel pump fuse. It will "prime" for about 2 seconds when you turn the key from OFF to ON each and every time. It will give constant power to the fuel pump when cranking the starter, obviously.

I don't know the difference between those relays, but there isn't anything special about them. I believe both are just normal 4 pin relays. You should just make sure the pin-outs are the same, they usually have a diagram with the pin numbers right on the relay housing. If the power to fuse 29 is turning on and off correctly (with the key) it should be fine to try and start it. If it is not shutting off with the key, that would be the only cause for concern.

I'll try and get you that diagram this evening when I get home.

I going to pick up the battery tomorrow morning. I got hung up doing things around the house so i wouldn't get in trouble with my wife If you can send me those diagrams that would be great. I sent you a pm last night.

[walky_talky20]

Sent you the diagrams for a 2000 1.8T. Wasn't sure whether your car was a 2000 or 2001, but the diagrams should be the same for this part.

[grillhands]

Sent you the diagrams for a 2000 1.8T. Wasn't sure whether your car was a 2000 or 2001, but the diagrams should be the same for this part.

Thanks bro. Those diagrams are nicely detailed. I'm gonna mess with it this weekend. I also picked up a crank position sensor because I've read that it could be a possible source to my engine problem. My car is a 2001.5 awm

[grillhands]

Update: i started to use my multimeter and i followed what this said http://www.audicrazy.com/repair/Audi_ECU_J271.pdf I found out that i don't have 12volts to pin 4 on the relay harness. It barely registers anything. Everything else came out fine. I'm going to mess with it a little more while my son is still sleeping lol.

Edit: I made a mistake. It should read 12v when you apply the ground wire to it. My battery is 12v but the reading is 11.6v so the white/black wire is acting as a ground as it should.

Edit2: I'm only getting .3v to pin one on the coilpack as well and that should be 12v.

Edit3: the power i get to fuse 29 is .8v. I'm trying to trace it back but in the schematics is goes to the relay plate and i'm not sure what that is. If it's the fuel pump relay i've already changed it.

[grillhands]

UPDATE!!!! I will be getting my car back tomorrow from Dan's automotive and it is running like a beast. I'm so happy because the car has been down for like 2 months. The culprit was a loose wire at the ecu which connected somewhere into the dashboard. This caused my no spark and ecm code. I'm going to start to break it in and plan on going with a 50trim lol. I want low 12s with the my setup. Walkytalky, thanks for all your help as well.