Potrice

Hey everyone,

I get the P20B9 check engine light (Reductant Heater A Control Circuit/Open) but the suv seems to run fine. I initially thought the problem was the heater crapping out but I think it's a wiring issue since I don't get the X amount of starts left on my dash. Also, if the heater crapped out, the def would freeze in the -30C temperature we had here in Ontario.

Anyways, so I proceeded to drop the tank and accidentally broke the long/slim black nozzle on the def fluid pump (I was pissed). Do I need the change the entire pump now? Gluing the small piece back in doesn't seem possible. Anyone else with the P20B9 code that could help? A part of me wants to say ?&*( all of this crap and put the chip/emulator in and never touch the crappy SCR system ever again.

VIN = 4JGDA2EB4DA231578

Thank you in advance!

turbosl2

I have a cloned MB STAR diagnostic tool/laptop i bought from aliexpress. I would invest in this because what i learned with the MB is that nothing can be replaced on this car without learning it to the vehicle, not even a battery. Terrible engineering. They will never get my money again. Buy the tool and it will pay dividends in the end, especially when you need a NoX sensor for the diesel. They also come with the factory service manual, photos...complete shop manaul

turbosl2

The code you have is for the pressure line and my diagram shows its on the actual pot assembly.

Found this on the net for the GL350, maybe it can help. I dont have time to fire up my MB star software

Potrice

Airflow Doctor

Have the same thing but here in NJ in March the temperature does not get below the DEF freeze point so I’m waiting on the warmer weather to address the problem. My BlueDriver tool says the fault for this code is likely to be the pressure line heater or the SCR module. Mine has 125,000 miles and I’ve already replaced the tank heater at 105,000. Reading up on this some suggest when one component fails it’s best to replace them all.

I suspect the the reason you don’t get the count down indicator is it is only programmed to work off the tank level sensor. I was up in Vermont for a few days and it got down in the -30 C range and I had no problem either.

Airflow Doctor

Have the same thing but here in NJ in March the temperature does not get below the DEF freeze point so I’m waiting on the warmer weather to address the problem. My BlueDriver tool says the fault for this code is likely to be the pressure line heater or the SCR module. Mine has 125,000 miles and I’ve already replaced the tank heater at 105,000. Reading up on this some suggest when one component fails it’s best to replace them all.

I suspect the the reason you don’t get the count down indicator is it is only programmed to work off the tank level sensor. I was up in Vermont for a few days and it got down in the -30 C range and I had no problem either.

Potrice

Well, I just called the dealership and he said the code is for the def feed line heater. Of course, they don’t sell the feed line heater individually, so I had to order a whole new def feed line. The part is on back order and they’re shipping it from Germany...estimated time to get it is 10-15 days. I’ll keep everyone updated once I installed it. Now I’ll go start a new thread because my alternator just died...

peter2772000

You don't have emissions-testing, get the damn thing deleted and be done with it.

I posted on the alternator thread. BTW, did you buy this truck new?

Potrice

I just got a call from the dealer saying they received the part. I will replace it soon and will update if the P20B9 code is resolved. If, after that, I ever get more codes regarding the SCR system, I'm going to throw in the white towel and get the emulator.

Diabolis

The DEF does freeze at -30C (it freezes at -11C). The heater is there to thaw it.

You won't get the start count indicator right away for a number of reasons. MB shuts off the whole DEF injection system when the ambient and DEF temperatures are below 10C and/or the SCR cat is not up to operating temperature. Once the ambient temperature and DEF warm up above 10C and the SCR is able to reach operating temperature - which in the winter months here may not happen for hours after you've started driving - you will get the start countdown only AFTER YOU HAVE TRAVELED FOR 80 km after the CEL light first comes on. You'd also get the countdown if the DEF level in the tank drops below the minimum (not sure if it's the same on the ML but it is 0.8L on the Sprinters; the first DEF warning comes on at 5.5L and the second at 3L remaining).

Potrice

Thanks for clarifying good sir. I have received the DEF feed line from MB (took them 10 days to ship it from Germany) and I will be installing it this Friday. Hopefully, this will take care of the check engine light issue.

Diabolis

Anytime. And yes, IIRC a P20B9 error indicates a pressure line heating element failure. You can't just replace the heating element - it's basically a metallic film that's wrapped around the pressure line that goes from the DEF tank to the metering valve near the front of the exhaust, so you need to replace the line. On the W164 there were a number of connectors along the way where you could check the individual heater segments with an ohmmeter, but I don't know if the design has changed on the W166. It is not a common failure. Were you driving in deep snow or otherwise scrape the bottom of the car by any chance?

Potrice

Negative. I didn’t hit anything or drive into deep snow. I just started the truck on a cold morning and the CEL popped. I love the truck but I got hit hard with wear and tear repairs for the last 2 months. 1 wheel bearing, 1 rear wiper motor, 1 alternator (1000$ up the wazoo), 1 rear shock was shot (replaced both) and now the def pressure line heater. Hopefully, I’ll be good for a while. The truck was problem free for the last 100k-110k km. It is now sitting at 174 000km.

I was thinking of trading it in for a brand new Santa Fe (they’re really nice imo). Went for a test drive and everything was good, but going from Hyundai to MB was brutal...no where near the amount of comfort. The new Santa Fe was just as equipped as my 2013 ML BT though. I guess they caught up in technology for the last couple of years lol.

Diabolis

Hope it all works out with the DEF line heater. l get to drive a number of different cars and I usually end up getting rid of my own before they reach 100K km, but from what I am seeing it seems that most luxury cars made in the last 8 years are actually designed and built to fall apart after a certain mileage and/or time.

Interesting re the Santa Fe... I recently drove an E53 for a couple of days and then a Genesis G80 (with the 5L V8 NA engine) for a week. The entire time I was in the Genesis I was thinking that the moment the GV80 hits the market I'll buy one. Once you get past the glitzy but ultimately frustrating video game in the form of the new MBUX system and dashboard in the E class, the G80 drives and feels every bit as good as the new E53 without the look-at-me pretentiousness of the "budget" AMG Merc and only costs 2/3 as much to boot. People are vain and most of them buy cars for the badge (and sadly with an E53 they don't even realize that all it says is "I couldn't afford the real one"), but once you look past the badge and instead objectively compare the quality of the product itself, it would be very hard to make a case for an E class, a 5-series BMW or an Audi A6 over a over that G80 Huyndai. So yeah, that Santa Fe may be only 80% as good as the Merc, but it is a 500% better value. A more refined Genesis GV80 will be 98% as good as the GLE Merc and still cost 2/3 as much. Once you factor in the warranty and the service, it's a no brainer.

Potrice

So I put the ML on the lift and proceeded with the job. The first half of the installation (from the exhaust to about half the length of the car) was easy. The second half (from the middle where it bolts on the frame all the way to the def tank pump) was another story...one heck of a job. The def feed/pressure line (whatever you wanna call it) was going above certain wires and into the upper part of the frame. Very hard to reach and a good thing I don’t have big hands. To remove the old one and install the new one, I had to remove the fuel tank support bracket, remove the rear passenger side wheel to have access to the def feed/pressure line.

All in all, it took me about 2 hours, taking my time, while enjoying a beer. I then used my Bluetooth OBD2 reader and cleared the check engine light. Hopefully, this will take care of the problem. I’ll keep this thread updated if it comes back (I really hope not).

Diabolis

I am assuming the CEL hasn't returned since you replaced the pressure line?

P.S. Just curious - did you see any places on the old one where the heater may have been damaged by mechaical abrasion?

Potrice

Correct. The CEL is gone. Regarding the inspection of the old one, I found nothing out of the ordinary. Everything seemed fine except that it was covered in road junk. I guess that salt and dirt got in the exhaust insert. Can't tell 100% for sure though.

Bern6389

which one did you buy?

excal

FYI, had this done at the dealer as I didn't have access to a lift. Came out to about $1000 CAD. If it were the in-tank heater there are places like Xemodex that will refurbish your part with better quality components, but no such option for the heated line.

Potrice

Ouch! I did this on a lift and it was a huge PITA. I can't even imagine doing this crawled under the suv...crazy! By the way, the 1000$ amount seems weird to me. The part cost me about 350$...so 650$ in labour? Hard to believe they would charge more than 2 hours for this job...stealerships!

excal

Just checked my invoice. It was 4h labour at $169/hr plus $285 for the part plus HST for a total of $1095, because nothing at the dealer costs less than a grand!

Potrice

Update: The CEL hasn't returned. I just wanted to let anyone know that if you broke the nipple of the Adblue/DEF pump, you can get the nipple repair kits here: https://xemodex.ca/ca/product/nipple...very-pumps-mb/

I also recommend getting the DEF tank heater kit from Xemodex, since the build quality far exceeds the OEM heater. Also, you get lifetime warranty.

Diabolis

+1 on the Xemodex DEF pump & heater rebuilds. No personal experience but I've heard only positive feedback from folks that are using them (and I know a bunch).

ketanpunde

Sorry, for intruding into an old thread, I am a newbie in this forum, newbie owner of 2014 ML350 Bluetec (90,000kms). I had a check engine light on a abruptly weather changed cold morning (night it was +11 and morning -13). The code was P20BE "Reductant Heater "B" Control Circuit Performance". I didnt erased the code, drove the car for 200kms. returned to the used car dealer.Dumb question and I am sure you guys are experts. I hope everyone is aware of the Emission Performance Warranty and the Related Components covered for 8yrs and 130,000 kms. Just saying. https://www.mercedes-benz.ca/content...s_Warranty.pdf

Diabolis

The DEF tank heater is not covered under the 8 year emission system warranty. See page 22 in the PDF you linked for what specific items are covered.