Archives for August, 2013

2 Posts

Flashing Check Engine Light & Coil Pack (MK4 Jetta)

In Spring 2013 I was driving to the gym and all of a sudden my Check Engine light (CEL) began to flash (orange color). My car began to stutter and vibrate unnaturally. Immediately I pulled over and turned off the car.  I waited about 1 minute and turned the car back on– the CEL was still flashing yellow and the car was stuttering. I decided to go to the gym and come back after an hour to try and turn it on again. When I came back the car was no longer stuttering! But the CEL light remained on (wasn’t flashing though). I took the car back home in Toronto and drove it for a week without issues. The car would stutter a bit only on start-up but would go away once the engine temperature rose.

I noticed the problem with the flashing CEL / engine stuttering would usually only come up on a cold engine and when it was moist outside (after rainfall or light snowfall in the spring).

After a week I drove back home to Windsor (about a 250 mile /400km drive) without issues.

When I got home the first thing I did was scan my car. I was getting codes for Cylinder #2 misfiring and short to ground codes for the cylinders.
Upon some investigation and research it turned out to be the Coil Pack. Physically, the coil pack from the outside looked fine, but upon closer inspection I noticed fine hairline cracks (very small). I found the majority of the cracks around the 2nd input for the ignition cable, which also matched up with the Cylinder #2 misfire. The were some other cracks around other ignition lead inputs as well.

Cracked Coil

My first attempt at fixing this was covering the cracks with epoxy. This seemed to work but about a month later I was washing my radiator and engine bay and upon start up the car up the car started to stutter and the CEL was flashing. At this point I gave in and bought a new coil pack from AutoZone(~$260 USD).

These cracks were so small that you wouldn’t notice them unless you unscrewed the coil pack and took the unit out and examined it closely under light. The fine hairline cracks was all that was needed to create tiny electric sparks in the dark that caused it to short.Ever since replacing my coil pack and ignition cables my issue with the flashing CEL and stuttering has been resolved.

Parts needed (VW part numbers):

06A-905-409-N  –  IGNITION LEADS (Cables)

06A-905-097  – COIL PACK


Fuel pump relay & Check Engine Light (MK4 Jetta)

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.

Once I scanned the vehicle, a list of codes came up for me:

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.

ECM Relationships

ECM Relationships

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!

Old 8 Pin Fuel pump relayIMG_0121

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