02 VW Jetta TDI with ALH engine glow plug

There is no throttle body on a TDI, but continuing to crank you engine with no fuel pressure will absolutely fry your pump and/or injectors (An '03 could be either an ALH or a PD engine, - different fuel injection systems, but same disastrous result in either).
Here's my .02:
DO NOT let a VW dealer touch your TDI. They commonly throw parts at it until the problem either goes away or they throw up their hands and say "I dunno". Either way, people routinely waste a boatload of time and money with no relief when taking their TDI to a VW dealer.
Go to TDIClub.com and look for a trusted TDI Guru near you (there's a list by state) and have one of these guys look at it. They're very helpful and more knowledgeable than 95% of VW dealers.
Good luck.

Replace your Glow plugs.

In addition to the 4 primary glow plugs, the cooling system also has 3 Coolant Glow Plugs to help provide extra heat to the cooling system in order to warm-up the vehicle's interior more quickly, and enhance overall engine warm-up time. (Example - Some Mercedes diesel engines use electrical heaters in the cabin because their engine is so thermally efficient.)
Likewise, this auxiliary source of heat from the 3 Coolant Glow Plugs is necessary because of the VW 1.9 TDI engines outstanding efficiency, which wastes very little heat.

The 3 Auxiliary Coolant Glow Plugs are located at the end of the aluminum cylinder head (in a protruding flange) directly below the vacuum (brake booster) pump, which also connects to a coolant hose.



The 3 Auxiliary Coolant Glow Plugs use two (underhood) relays which are monitored and controlled by the ECU. During a cold start, the vehicle's interior temperature selector switch helps the ECU choose one of three modes depending on the amount of heat required to warm-up the coolant.

For example, Coolant Glow Plug #1 can be selected to operate all by itself, or #2 and #3 can operate together as a two-some, or lastly, all three glow plugs can form a triple source of heat for maximum enhancement of engine warm-up time.

After the engine is completely warmed up and the thermostat is open, the Coolant Glow Plugs normally shut-off and remain off unless the (thermally efficent) engine cools down sufficiently to have the computer signal them to come back on to keep the engine and cabin air warm. Extensive idling times at stop lights or in the driveway are scenarios where these glow plugs are most likely to recycle on and off.

In conclusion, the period of Preglow and Afterglow is determined by the engine's coolant temperature (during a cold or hot start), which helps the ECU select a predetermined time-cycle for the combustion chamber and / or Auxiliary Coolant Glow Plugs to follow.

Finally, one myth that needs to be immediately debunked, is the belief that the TDI's advanced Glow Plug System is linked to the opening of the driver's side door, which is false! It is also noteworthy to mention that some earlier VW diesel glow plug systems were operated in this manner, but not so with the advanced VW Jetta 1.9 TDI engine.



Please do rate my response. Thanks!

In addition to the 4 primary glow plugs, the cooling system also has 3 Coolant Glow Plugs to help provide extra heat to the cooling system in order to warm-up the vehicle's interior more quickly, and enhance overall engine warm-up time. (Example - Some Mercedes diesel engines use electrical heaters in the cabin because their engine is so thermally efficient.)
Likewise, this auxiliary source of heat from the 3 Coolant Glow Plugs is necessary because of the VW 1.9 TDI engines outstanding efficiency, which wastes very little heat.

The 3 Auxiliary Coolant Glow Plugs are located at the end of the aluminum cylinder head (in a protruding flange) directly below the vacuum (brake booster) pump, which also connects to a coolant hose.


The 3 Auxiliary Coolant Glow Plugs use two (underhood) relays which are monitored and controlled by the ECU. During a cold start, the vehicle's interior temperature selector switch helps the ECU choose one of three modes depending on the amount of heat required to warm-up the coolant.

For example, Coolant Glow Plug #1 can be selected to operate all by itself, or #2 and #3 can operate together as a two-some, or lastly, all three glow plugs can form a triple source of heat for maximum enhancement of engine warm-up time.

After the engine is completely warmed up and the thermostat is open, the Coolant Glow Plugs normally shut-off and remain off unless the (thermally efficent) engine cools down sufficiently to have the computer signal them to come back on to keep the engine and cabin air warm. Extensive idling times at stop lights or in the driveway are scenarios where these glow plugs are most likely to recycle on and off.

In conclusion, the period of Preglow and Afterglow is determined by the engine's coolant temperature (during a cold or hot start), which helps the ECU select a predetermined time-cycle for the combustion chamber and / or Auxiliary Coolant Glow Plugs to follow.

Finally, one myth that needs to be immediately debunked, is the belief that the TDI's advanced Glow Plug System is linked to the opening of the driver's side door, which is false! It is also noteworthy to mention that some earlier VW diesel glow plug systems were operated in this manner, but not so with the advanced VW Jetta 1.9 TDI engine.

Before you invest in a long drawn out Glow Plug replacement etc. A little known issue occurs on the ALH TDI engines. The temperature sensor sending unit. A small blue module that plugs into the coolant hose assembly will cause a P error on the glow plugs that is nothing to do with the glow plugs at all. The part fails and sends a temp error to the engine computer. I tested all the coolant glow plugs, engine glow plugs and glow plug harness and all worked fine. One of the test procedures for the glow plugs is to undo this sensor that will force the glow plugs to come on no matter what temperature. This confirmed my GP system was functional and the sensor was bad. I purchased the part from local VW dealer for $33 US and installed and it is fine. Dependent on your model it can be square or round. The link to this part for your car is http://www.partsgeek.com/catalog/1997/volkswagen/jetta/body_electrical/water_temperature_sender.html

Be sure to have VW Pentosin coolant on hand to refill coolant system as you will lose quite a bit when removing this part. It is located slightly behind the coolant glow plug assembly.. This is the round ones not the ones on the engine block at top.

Be sure that when you replace it you put in a new rubber gasket seal.. its a round rubber seal that should come with your new part. Dont reuse the old one or you will have a leak.

There is a c-clip that holds this in the hole you slide that clip off and wiggle the sensor out. Coolant will run out of the hole, so do this outside. The sensor is easily pulled out. You will need to insert the new part in teh same hole with new rubber gasket and replace c clip. Then plug in wiring harness and you should be good to go.

glow plug light comming on when driving . starting ok. check your brake lights are working.

your glow plug relay is going out you need to replace it.

Ok , ok. Give me some more information and we'll solve this. We're talking about a jetta TDI 2000 with an ALH engine code I figure.
#1 Do you have an faults recorded in the ECM like a check engine.
#2 Are you using synthetic oil 5W40 preferably Castrol?
#3 How old is your fuel filter?

replace the relay but check connections first as often connection get hot and corroded.failing which buy a push button switch use a relay and and some heavy wire to and from relay to the heaters and work them manually.you could try seperating the relay and cleaning the connections inside.

glow plug relay is going out