MK4 1.9 BEW Throwing Multiple Sensor Codes-- ECM? BCM? (or Harness?)

[Zacque]

Hey there, I have a BEW TDI with just over 215,000 miles on it. I've owned it for a little over 6 years. I replaced the alternator about 6 months ago, and the battery last month. Despite this, when I start the vehicle now it pops the Battery, Brake, ABS, and Air Bag lights, but they are confusing. Sometimes they flicker as I start or drive, and sometimes they stay until I put the car in drive and hit the gas.

Also, the EGR was ripped out the end of 2019.

I ran VCDS on it and it came up with these codes:

Engine:
P0407 EGR Sensor 2 (not sure how to clear it)
P3007 Camshaft Position Sensor G40
P0118 Engine Coolant Temp Sensor G62
P0101 Mass Air Flow Sensor G70

Trans:
Transmission Fluid Temp Sensor G93
Brake Light Switch F

Airbags:
Supply Voltage B+

Central:
Window Regulator Switch E40 Front Left (this has gone out before, the new one in the driver door is no more than 2 years old. I replaced the switch and the locking solenoid.)

Thank you so much, the posts and comments from this site have helped me fix my car numerous times over the years. Any insight or advice or pointers would be a huge help !


My concern with all of this is that there is a larger electrical issue in the car. I wonder if it could be the Engine Control Module or the wiring harness that runs from the ECM to all these sensors. Have anyone seen this before in an ECM failure? Or do you have a hunch of what the true problem could be?

 

[STDOUBT]

Have you checked/cleaned all your grounds?

Golf/Jetta IV Ground List

 

[tdi_my live]

The main ground cable is located under the battery. Check out the poles. Clean everything nicely and reinstall.

 

[Tdijarhead]

I assume you replaced the alternator because it wasn’t working? Did you buy it from an auto parts store? You recently replaced the battery, because it wasn’t working either?

To me it sounds like the recent alternator you put in isn’t doing it’s job. Auto parts store alternators, starters etc are often junk. Get a digital multimeter ($30 Walmart) you tube how to use it if you don’t know.

Sitting in your driveway with the car off a new battery should show around 12.7v a well used but good battery should be from 12.4-12.6 a battery which will need replacing soon, probably at the onset of cold weather will be 12.2-12.3, below that and starting your car can be a challenge, in addition to the cars ecu throwing a bunch of random codes.

With the car running the voltage at the battery should jump to around 14v generally 13.8-14.2 that is the voltage the alternator is generating. If it’s down below 13.3 or so the alternator is not keeping up with the electrical demands of your vehicle, I really wouldn’t like to see anything below 13.5 with all the cars accessories running. With all the accessories off it should be right at 14 ish.

Borrow or buy a multimeter and dig a little deeper.

 

[oilhammer]

Yeah, the parts store alternators are garbage, and cause all sorts of problems. Genuine Bosch is the only way to go. 120A if it is a manual, 90A if it is an automatic (but the 120A is usually more common, and often cheaper, so I'd just put that on there, it won't hurt anything).

Also in addition to the grounds, make sure the fuse link box and all its connections, especially from the alternator, are good and nothing is burnt or melted.