DEF Heater Unit Replacement DIY Procedure
02-12-2021 | 10:50 AM
#1
Thread Starter
Senior Member
Joined: May 2013
Posts: 437
Likes: 83
From: Espoo, Finland
2012 GL 350
DEF Heater Unit Replacement DIY Procedure
Hey all, I replaced the DEF heater on my 2012 GL350; other years/models may be similar.
So before Christmas I got dash message that DEF was running low and I immediately went out and got 10L and dumped it in. Strangely the message would occasionally return, but I never got to the countdown. We went back to the US for 3 weeks over the holidays, and when I got back it was OK for a couple weeks, then the same message popped up. I bought another 10L and put in about 8 and that shut it up. Then, about a week later I got a persistent check engine light for P20BE which suggests heating element failure. I reset the light multiple times but it was pretty clear it was dead. At this point I started shopping for a replacement part. The cheapest available are on eBay but most of the sellers of the least expensive units are in the USA and China. I don't buy stuff from China and this whole Covid mess has really made ordering things from overseas a challenge because there are so few flights, and it's been quite cold here (0-15 degrees F for daily highs, or -12 to -18 degrees C) so I didn't want to let it go for long, not knowing what damage might be caused if the DEF froze. I found the XModEx site and they looked like they would ship express for no additional cost, and since it was actually less than buying locally or from Germany/UK (my normal spots for car parts these days) I went ahead and ordered from them. Sure enough, the part arrived in 2 days via UPS. I did screw up, forgetting that when ordering something this expensive (it was USD$527 with a 5% off coupon code I found) that you have to pay VAT, which here in Finland is 24%. Ouch. You've been warned; socialism sucks.
Anyway, today I installed the unit. I unfortunately didn't take any photos since I had left my phone in the house and I was already under the car and dirty. I've uploaded the WIS procedure which has some pictures.
1. First off you jack up the rear of the vehicle as high as you can. In order to drop the tank, you need to make some space, using jack stands under the rear jack pads.
2. Next you crawl underneath and go to the forward portion of the tank. There you will see the DEF line on the passenger side (USA/Non-UK) of the tank, along with an electrical connector. To disconnect the DEF line you put a pair of pliers on the outer ring by the knurled sections and gently squeeze while prying, and it will pop right off. The small electrical connector, you push out the grey tab, then pull.
3. Next I found it necessary to drop the exhaust; just the rear silencers/mufflers. There are 4 bolts holding each, 13mm. I used an electric impact and this was fast/easy. I also had to pull the Torx screws from the exhaust trim at the muffler outlets in order to pull the exhaust down since the exhaust tips just extend inside of them.
4. At this point, with the exhaust out of the way, you remove the plastic protective cover for the tank. It's held on by 4 10mm plastic nuts and comes off easily.
5. Now you need to position a jack (my tank was full, if yours is empty or near empty you may not need to) underneath the tank. I used a square piece of plywood to make it more stable and positioned the jack right beneath the round portion of the bottom of the tank. With the jack in position, you remove the 4 nuts that hold the 2 metal straps. I think these are 12 mm, but maybe they were 13. Anyway, as you remove them the tank will then be supported by your jack. Slowly lower the jack until you can access the two electrical connectors at the rear of the tank. Disconnect these connectors, and continue lowering the tank until you have it as low as it will go. Then slide the tank out (to the side if you have a trailer hitch) and then set it on the floor (if full.)
6. At this point, there are good instructions provided by XModEx, but I'll briefly describe what you do. There is a pump on top of the tank which you remove by unscrewing three 4mm hex bolts. You have to disconnect 5-6 electrical connectors and remove some zip ties from the large nut on the top of the tank that holds the heater down. Once these connectors are out the way, you lift the heater out of the way, exposing the large, round nut. This nut is just like the nut that is used to hold down most fuel pumps. To unscrew it, XModEx provides a tool, but you can also loosen it using a large screwdriver and a mallet/hammer to tap on the large edges. Just be careful not to break the nut.
7. Now that the nut is off, you pry the top of the heater up with a screwdriver and pull out the large rubber seal that holds it in place. At this point, you need to unscrew the plastic cylinder counter-clockwise about 1/8 turn. This is tricky because the DEF is slippery. I found the best way to do this was to put on some long gloves and reach down the bottom of the tank and use the metal heating element to turn it. Once loose, pull the cylinder out of the tank. There is a filter on the bottom that you can twist off to let the DEF drain out.
8. If you've bought a unit that comes with the new cylinder, then you can skip this step, but the XModEx kit requires that you remove the old element and level sensor and reuse the cylinder. They provide a tool to remove the two star shaped press-fit fasteners, but I found that using a long flat blade screwdriver and a set of long needle nose pliers was easier. The level sensor is held in place with a U shaped pin. Once you have the new unit in place and have replaced the star fasteners and pin, you are ready to reinstall the unit in the tank.
9. First you put the rubber seal back in place (I rinsed it with water first.) Then you push the cylinder all the way down until it hits bottom. Again, I used my long gloves and used the heating element to turn it clockwise 1/8 turn to lock it in place. The top requires that you align two arrows, one on the heater and one on the tank. At this point, you screw the large nut back on to hold down the heating unit either using your tool or the hammer method. Then you use new O-rings to reinstall the pump. There are two of these, one small and donut shaped and on cylindrical with a hollow center. The small one you place on the nipple of the pump, but the cylindrical one you place about 1/3 of the way into the heating unit assembly. Then you carefully push the pump into place and replace the three small bolts. Reconnect the electrical connections and put your zip ties back in place.
10. The rest of the job is the reverse of disassembly. There weren't any gotchas that I can think of except that I had the whole thing put back together and realized that I forgot the plastic cover. So I had to drop the exhaust again and install it, then do it all over. Oh well,
Total time was 4 hours; 3 1/2 if you don't have to drop the exhaust a second time, and you don't lose one of the nuts that holds the cover in place and then have to pull a new one out of your workbench after fruitlessly searching for it for 10 minutes.
Reset the check engine light and you're done.
So before Christmas I got dash message that DEF was running low and I immediately went out and got 10L and dumped it in. Strangely the message would occasionally return, but I never got to the countdown. We went back to the US for 3 weeks over the holidays, and when I got back it was OK for a couple weeks, then the same message popped up. I bought another 10L and put in about 8 and that shut it up. Then, about a week later I got a persistent check engine light for P20BE which suggests heating element failure. I reset the light multiple times but it was pretty clear it was dead. At this point I started shopping for a replacement part. The cheapest available are on eBay but most of the sellers of the least expensive units are in the USA and China. I don't buy stuff from China and this whole Covid mess has really made ordering things from overseas a challenge because there are so few flights, and it's been quite cold here (0-15 degrees F for daily highs, or -12 to -18 degrees C) so I didn't want to let it go for long, not knowing what damage might be caused if the DEF froze. I found the XModEx site and they looked like they would ship express for no additional cost, and since it was actually less than buying locally or from Germany/UK (my normal spots for car parts these days) I went ahead and ordered from them. Sure enough, the part arrived in 2 days via UPS. I did screw up, forgetting that when ordering something this expensive (it was USD$527 with a 5% off coupon code I found) that you have to pay VAT, which here in Finland is 24%. Ouch. You've been warned; socialism sucks.
Anyway, today I installed the unit. I unfortunately didn't take any photos since I had left my phone in the house and I was already under the car and dirty. I've uploaded the WIS procedure which has some pictures.
1. First off you jack up the rear of the vehicle as high as you can. In order to drop the tank, you need to make some space, using jack stands under the rear jack pads.
2. Next you crawl underneath and go to the forward portion of the tank. There you will see the DEF line on the passenger side (USA/Non-UK) of the tank, along with an electrical connector. To disconnect the DEF line you put a pair of pliers on the outer ring by the knurled sections and gently squeeze while prying, and it will pop right off. The small electrical connector, you push out the grey tab, then pull.
3. Next I found it necessary to drop the exhaust; just the rear silencers/mufflers. There are 4 bolts holding each, 13mm. I used an electric impact and this was fast/easy. I also had to pull the Torx screws from the exhaust trim at the muffler outlets in order to pull the exhaust down since the exhaust tips just extend inside of them.
4. At this point, with the exhaust out of the way, you remove the plastic protective cover for the tank. It's held on by 4 10mm plastic nuts and comes off easily.
5. Now you need to position a jack (my tank was full, if yours is empty or near empty you may not need to) underneath the tank. I used a square piece of plywood to make it more stable and positioned the jack right beneath the round portion of the bottom of the tank. With the jack in position, you remove the 4 nuts that hold the 2 metal straps. I think these are 12 mm, but maybe they were 13. Anyway, as you remove them the tank will then be supported by your jack. Slowly lower the jack until you can access the two electrical connectors at the rear of the tank. Disconnect these connectors, and continue lowering the tank until you have it as low as it will go. Then slide the tank out (to the side if you have a trailer hitch) and then set it on the floor (if full.)
6. At this point, there are good instructions provided by XModEx, but I'll briefly describe what you do. There is a pump on top of the tank which you remove by unscrewing three 4mm hex bolts. You have to disconnect 5-6 electrical connectors and remove some zip ties from the large nut on the top of the tank that holds the heater down. Once these connectors are out the way, you lift the heater out of the way, exposing the large, round nut. This nut is just like the nut that is used to hold down most fuel pumps. To unscrew it, XModEx provides a tool, but you can also loosen it using a large screwdriver and a mallet/hammer to tap on the large edges. Just be careful not to break the nut.
7. Now that the nut is off, you pry the top of the heater up with a screwdriver and pull out the large rubber seal that holds it in place. At this point, you need to unscrew the plastic cylinder counter-clockwise about 1/8 turn. This is tricky because the DEF is slippery. I found the best way to do this was to put on some long gloves and reach down the bottom of the tank and use the metal heating element to turn it. Once loose, pull the cylinder out of the tank. There is a filter on the bottom that you can twist off to let the DEF drain out.
8. If you've bought a unit that comes with the new cylinder, then you can skip this step, but the XModEx kit requires that you remove the old element and level sensor and reuse the cylinder. They provide a tool to remove the two star shaped press-fit fasteners, but I found that using a long flat blade screwdriver and a set of long needle nose pliers was easier. The level sensor is held in place with a U shaped pin. Once you have the new unit in place and have replaced the star fasteners and pin, you are ready to reinstall the unit in the tank.
9. First you put the rubber seal back in place (I rinsed it with water first.) Then you push the cylinder all the way down until it hits bottom. Again, I used my long gloves and used the heating element to turn it clockwise 1/8 turn to lock it in place. The top requires that you align two arrows, one on the heater and one on the tank. At this point, you screw the large nut back on to hold down the heating unit either using your tool or the hammer method. Then you use new O-rings to reinstall the pump. There are two of these, one small and donut shaped and on cylindrical with a hollow center. The small one you place on the nipple of the pump, but the cylindrical one you place about 1/3 of the way into the heating unit assembly. Then you carefully push the pump into place and replace the three small bolts. Reconnect the electrical connections and put your zip ties back in place.
10. The rest of the job is the reverse of disassembly. There weren't any gotchas that I can think of except that I had the whole thing put back together and realized that I forgot the plastic cover. So I had to drop the exhaust again and install it, then do it all over. Oh well,
Total time was 4 hours; 3 1/2 if you don't have to drop the exhaust a second time, and you don't lose one of the nuts that holds the cover in place and then have to pull a new one out of your workbench after fruitlessly searching for it for 10 minutes.
Reset the check engine light and you're done.
