Recently my car has had issues starting sometimes and my Check Engine Light (CEL) has been on. Car starting issues can be quite stressful if they happen at the wrong places or time so I decided to note my experience with this issue.
The first step is to SCAN YOUR VEHICLE. I personally have my own scanner but you can scan it anywhere. The CEL by itself doesn’t mean anything to you until you diagnose the problem.
If you examine the codes, you can see that they all have reference to ELECTRICAL related issues (short to ground, low voltage etc..). This lead me to believe that it is most likely some kind of wiring issue because it’s highly unlikely that all of those components failed simultaneously. I then took a look at the Bentley manual and found a diagram that showed the relationship between the ECU and other electrical components.
Looking at the diagram you notice that all those components were coming up on the scanner. Between the ECU and all the components (O2 sensor, Vacuum pump, etc..) I noticed that the fuel pump relay was interacting with everything.
The first thing I did was check the fuel pump relay. The fuel pump relay on this car gets primed every time you open the driver door. Sometimes I noticed it wasn’t priming and when this happened the car would not start or have a very rough start. The relay is located under the steering wheel. It has the number “409” written on the back of it. It is a small box with a width of about 1 inch. The fuel pump relay is almost like a plug. It has contacts that plug into an outlet making this quite an easy fix (you do not need to pay a mechanic for something as simple as this). Swap your old relay with a new one from the dealership.
My old relay was an OEM VW part and it had 8 PINS. The relays seem to have undergone a redesign and are now 7 PINS. I verified this with VW of America. You will see that pin #7 is missing in the newly redesigned relays.
I first bought the generic brand relay from Autozone and tried it(was a 7 PIN relay). The car would start fine BUT if you opened the driver door while the car was running it would SHUT OFF COMPLETELY. I’ve read reports that other generic brands like NAPA also have this issue. I’m not sure as to why because both the OEM and generic brand have the same circuit structure printout that you can see on the relay.
In short the new OEM relays are 7 PINS and they WILL WORK with your Jetta (MK4). The NON OEM relays that are 7 PINS WILL NOT WORK because as soon as you open the door while the car is running or you are driving your car will shut off!
Once I swapped my old relay with an OEM relay the car started smooth as it should and the CEL was gone once I cleared it with the scanner.
Parts needed (VW part numbers):
1J0 906 383 C – Fuel Pump Relay