Pelican mechanics... Obd2 codes(Vw)...
 

I have a Vw 1.8 turbo that won't start.... wife says the air conditioning, turn signals wouldn't come on , then she drove it 25 miles home... next morning it wouldn't start. Hooked up code scanner and got P1237, P1238, P1239, P1240 Manufacturer Control Air Metering. Looked up says cylinder 1-4 fuel injector open circuit. Any ideas?

do bad coils throw a code?

Check to make sure you have voltage supply to one side of each injector. The computer grounds the other side to pulse the injector. ( the fault code dictates you probably don't ). And with other electrical things not working, I would start by checking all the fuses and such.

I'd bet your alternator just failed

You know, Eric is a smart guy. I was sort of thinking similar when I first read your post. Does the battery/starter spin the motor, or is it all dead? They will throw all sorts of codes, once system voltage drops below the 9-10 volt range. I'll do the best I can to help you out here. I have never seen a vw ecm fry its injector drivers , but that does not mean it is not possible. Could also be a blown fuse that supplies voltage to the injector circut.
Keep us posted.

more info.... the fuel pump is not running when I turn the key on. So I hooked it up to a 12 volt battery and it runs. Then I kept it hooked up but it still wouldn't start. I read where it needed 70 psi to open up the injectors. Then I pulled the fuel line off the injector rail and turned the key on, plenty of fuel but probably not 70 lbs. Checked all fuses and replaced fuel pump relay. Checked voltage at injectors read at 3.47. Replaced alternator, no go. I'm thinking maybe fuel pump is just starting to go? THANKS for all suggestions will work on it more tomorrow an let you know. All suggestions appreciated...

A bad fuel pump wouldn't cause the turn signals or air conditioning to shut off

I'm not sure about those older VWs, but I know Honda uses a ELD electrical load detector that slowly goes bad and wreaks havoc, and eventually burns out the alternator and battery

It does not need any fuel pressure to open the injectors, they are opened electrically, and will shoot fuel even if there is only 10 psi. I think system pressure is somewhere around 45 psi. I think you need to find the root cause of that 3.4 volts on the injector harness. You should have 12v. You have a broken wire, faulty relay, or bad module somewhere. If you give me some more specifics as to what year/model you are working on, I can get you some wiring diagrams, and that may help you to chase it down a little better.

See if you can find someone with a Vag-Com or real VW scanner, the 1.8t have a real good diagnostic system, but a generic scanner will not tell you exactly what is going on.

Turn signals and a/c are part of separate electrical system.
Even if the dash circuits are out, the motor should run.

I'm thinking check/replace battery, and clean all grounds(clip on a few extra wires to see if it works after). That could be causing the wonky computer.
Start from there.

Update in case anyones interested.... New Beetle 1.8 turbo. Checked #32 fuse twice couldn't see that it was broken then tried a new one and it started:). However the electrics were still on the blink. Took it to the dealership thinking it was either a relay or ignition switch(which according to the internet could involve burned wires). It was the dreaded ignition switch, took them 7hrs to fix cause of the wires , I watched from afar. Think the mechanic was bald by the end of it:D