As you may or may not know in most cases when the glow plug light flashes on your dash board (when driving!) its something to do with the brake lights or related electrical system.
The ideal when the glow plug light flashes (now to be refereed to as GPLF) is to connect to a VAG COM as what is actually happening is your ECU is telling you that there is a fault, GPLF it can be indicative of many things so connection to a VAG COM will let you know what it is for sure.
However........... As I said its normally something to do with the brake lights!
LED lights / modified bulbs
These will in most cases cause GPLF as the resistance of the bulbs is lower and thus the ECU thinks the light bulbs have blown, cure this instance of GPLF problem by use of of a MIL defeat loom.
At the time of writing both Brickwerks and T4'sR US sell them
First checks
Item number one to check, is are the lights going on and off?
- If so and only one bulb is operating then change it this should fix the GPLF.
- If so and both lights are working then you either have an intermittent fault with the switch (in which case attempt overhauling switch, as below) or you have another problem (in which case connect to VAG COM)
If the brake lights are not working at all then do the following in order:
1/ check both bulbs are not blown.
2/ check fuse number 20 (for brake lights) in the internal fuse box.
3/ overhaul switch
Overhauling switch
This took me 10 mins and saved a trip to the parts supplier, it is the easiest job in the world A:.
First of all remove the switch it is on a bracket above the brake pedal (note this switch is different to the clutch one which is a two pin). The switch has a plunger and 4 pins (the key is its above the brake pedal LOL mine was black in colour but I understand this is not always the case.
By hand twist the switch till it is free of the bracket. Then disconnect the plug. Pictures of the top of the switch, bracket and plug below for reference.
Pop the top off the switch which is retained by three clips you will be met with the below photo once fully dismantled
You will note that the switch is purely mechanical i.e. only moving components that make or brake two sets contacts thus this switch can easily be repaired.
Clean all the contacts to bright metal with contact cleaner and wire wool and reassemble the switch there are two sets (four) contacts to clean which are detailed below.
Picture of internal contacts you will need a small screw driver to put the wool on! (the one at the top of the screen had some crud in it which was my problem)
The other side of these prongs (1st pic) get hit by the other contact seen in 2nd pic (its the thin piece at just under the larger spring). The internal contacts get hit by the contacts under the bottom plate in the 2nd picture.
You can test the switch if you like by laying a multi meter on its most sensitive setting across first the two outer pins and secondly the two inner pins. The resistance should change instantly from 1 to 0 or 0 to 1 depending on which way you are going.
Then replace switch and job done.
Note if the switch is totally fried you'll need a new one GSF and VW sell 'em however this must be rare (if one has the part numbers to hand please add them in the thread or PM me).
Think this only applies to 2.5 Tdi engines but will stand corrected and edit as required :ILU:
The ideal when the glow plug light flashes (now to be refereed to as GPLF) is to connect to a VAG COM as what is actually happening is your ECU is telling you that there is a fault, GPLF it can be indicative of many things so connection to a VAG COM will let you know what it is for sure.
However........... As I said its normally something to do with the brake lights!
LED lights / modified bulbs
These will in most cases cause GPLF as the resistance of the bulbs is lower and thus the ECU thinks the light bulbs have blown, cure this instance of GPLF problem by use of of a MIL defeat loom.
At the time of writing both Brickwerks and T4'sR US sell them
First checks
Item number one to check, is are the lights going on and off?
- If so and only one bulb is operating then change it this should fix the GPLF.
- If so and both lights are working then you either have an intermittent fault with the switch (in which case attempt overhauling switch, as below) or you have another problem (in which case connect to VAG COM)
If the brake lights are not working at all then do the following in order:
1/ check both bulbs are not blown.
2/ check fuse number 20 (for brake lights) in the internal fuse box.
3/ overhaul switch
Overhauling switch
This took me 10 mins and saved a trip to the parts supplier, it is the easiest job in the world A:.
First of all remove the switch it is on a bracket above the brake pedal (note this switch is different to the clutch one which is a two pin). The switch has a plunger and 4 pins (the key is its above the brake pedal LOL mine was black in colour but I understand this is not always the case.
By hand twist the switch till it is free of the bracket. Then disconnect the plug. Pictures of the top of the switch, bracket and plug below for reference.
Pop the top off the switch which is retained by three clips you will be met with the below photo once fully dismantled
You will note that the switch is purely mechanical i.e. only moving components that make or brake two sets contacts thus this switch can easily be repaired.
Clean all the contacts to bright metal with contact cleaner and wire wool and reassemble the switch there are two sets (four) contacts to clean which are detailed below.
Picture of internal contacts you will need a small screw driver to put the wool on! (the one at the top of the screen had some crud in it which was my problem)
The other side of these prongs (1st pic) get hit by the other contact seen in 2nd pic (its the thin piece at just under the larger spring). The internal contacts get hit by the contacts under the bottom plate in the 2nd picture.
You can test the switch if you like by laying a multi meter on its most sensitive setting across first the two outer pins and secondly the two inner pins. The resistance should change instantly from 1 to 0 or 0 to 1 depending on which way you are going.
Then replace switch and job done.
Note if the switch is totally fried you'll need a new one GSF and VW sell 'em however this must be rare (if one has the part numbers to hand please add them in the thread or PM me).
Think this only applies to 2.5 Tdi engines but will stand corrected and edit as required :ILU: