P20BF - Reductant (DEF) Heater Circuit Low

14791 Views 18 Replies 6 Participants Last post by blackbird, Jun 27, 2018

blackbird

Discussion Starter · Nov 9, 2017

I picked up a new 6-speed '18 diesel hatch yesterday and already ran into an emission system fault. The dealer did an out of state trade so the car had about 200 miles on it and I put about a hundred more miles on it since yesterday. On the way back to the dealer tonight to pick up a car I left there, the new Cruze set a P20BF emission system check engine light with the reduced vehicle speed in xx miles warning.

Not having a scan tool with me I called OnStar and they ran a diagnostic which showed the P20BF. This appears to be for reductant heater circuit low (i.e. DEF tank heater faulty, short circuit or circuit open). One of the two times GM replaced the DEF tank on my first gen Cruze diesel was for the faulty tank heater so I was optimistically hoping to avoid problems on the new powertrain. With any luck this is just a one-off problem and not a systemic issue like the first gens.

I'll post up what they find after the service department takes a look tomorrow.

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1 - 19 of 19 Posts

91794

· #2 · Nov 9, 2017

Maybe is the reduced speed limitation only in forward gears ?

(For example, if the DEF runs out and speed is limited to 4 mph maybe a nice workaround is to drive a brisk 10 mph in reverse.)

blackbird

Discussion Starter · #3 · Nov 9, 2017

On the old Cruze and this one I've never driven it far enough to find out.

The dealer has called three times today, first thing in morning and then two updates that they're still looking. Apparently there were a few other cleared codes and he was wondering if the car was dead or had been jump started. They're still doing diagnostics on the DEF tank code.

blackbird

Discussion Starter · #4 · Nov 11, 2017

Update. While the service writer was great about communicating what was going on I went in to pick up my car, drove off, and under two miles later the check engine light was back on and "service emission system" countdown back. It's now showing a P20E8 code which comes back as reductant pressure too low (i.e. DEF pump not producing enough pressure).

Checking the invoice confirmed the P20BF code for reductant heater circuit low and also listed another "PH66" code which I think is a typo. The service writer mentioned seeing a code for a power surge and asked if the car had died or been jump started which I'm guessing was related to that other code.

I crawled around under the rear of the car and and the the drop-down cover/door that covers the DEF tank electrical connectors was partially hanging down. It also had the same mileage as when I dropped it off. I'm figuring the technician cleared the code, took a visual look at the connectors, let it idle a long time (which explains why when the service emission system error on the dash came back showing ~90 miles until speed reduced to 65 mph when it was much higher when I dropped it off) and didn't even do a drive cycle test spin around the block.

Back to the dealer tomorrow. In Massachusetts you have to have a safety and emission inspection done when purchasing a new or used car within 7 calendar days. Even if they don't get to it until Monday that means it would still need driving time to set the emission system readiness monitors (self tests) in the computer. So I'm probably going to have to get it tested, fail, have the dealer fix the problem, then take it back for emission system re-test. Not the best way to start off ownership on a new car.

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HondaTech2016

· #5 · Nov 11, 2017

Sounds like I'd be taking it to another dealer then, unless that's a pretty long stretch for you.

When my car showed the DEF fluid low after only 300 miles the local dealer (in town, 5 minutes from my house) told me I needed to take it back where I got it. I couldn't do that because they were over a hour away. I ended up getting a dealer about 20 miles out of town to look at it. Turns out the nozzle was broken.

Needless to say the dealer in town can royally f**k off now. I won't even let them do the free oil changes. Plus they've screwed my parents since then as well. But unlike my Dad I'm a man of principle, I'll spend extra time and money to prove a point.

To be clear the reason I didn't buy from them was because not only was the other dealer cheaper, but the local one still hasn't had a diesel on the lot yet that I know of.

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blackbird

Discussion Starter · #6 · Nov 12, 2017

Same here. I have a dealer with a great service department and so-so sales staff that's actually closer to home. I would have bought from them but they haven't ordered any new diesels, even though they're one of the largest Chevy dealers in the multi-state area.

I'm going to have a talk with the service manager Monday and see if they have a Duramax diesel certified tech that can take a look. The only reason I'm going back is to cover myself if this car turns into a basket case and I have to use the lemon law. Speaking of which, the car did fail Massachusetts state inspection today. The safety/emission check is required within 7 days of buying a car and if a new car fails and I took it somewhere and got an estimate that possible repairs could run over 10% of the car's price (even if it would be covered under warranty) technically the manufacturer already has to buy it back.

It's a nice car and I'm giving the dealer one last chance and a few days to sort it out. If they don't it's going back and they can wind down the deal and I'll order a different one somewhere else.

Technical note, the check engine light went out today but the diesel emission system light stayed on along with the countdown to reduce vehicle speed warning. It the regular check engine light came on again the next drive cycle and both the original P20BF code for the reductant heater circuit and the P20E8 for reductant pressure low are set as active. I'd suspect there's a wiring problem and the DEF tank isn't getting power or the harness was damaged on install. Have to wait and see what they find.

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blackbird

Discussion Starter · #7 · Nov 13, 2017

Dropped the car off at the dealer first thing this morning and asked if they had one of the diesel certified techs look at the problem. An hour later I got a call that they found the DEF tube from the tank at the rear of the car along with some of the electrical harness had been improperly routed in the engine bay, came into contact with the exhaust/cat and melted. They have to order a replacement which is a couple days out.

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Chevy Customer Care

· #8 · Nov 14, 2017

Hey Eric, we recognize how this can be frustrating and apologize for the new inconvenience. We want you to have the best ownership experience possible with your new diesel hatch. Our team would like the chance to touch base with your dealer regarding your DEF situation to ensure the appropriate parties are involved. Please feel free to send us a private message with your contact information, VIN, current mileage, and the servicing dealer if you're interested. Hope to hear from you soon.

Best,
Eddie A.
Chevrolet Customer Care

HondaTech2016

· #9 · Nov 14, 2017

Cool, looks like someone from Chevrolet cares to help.

blackbird

Discussion Starter · #10 · Nov 20, 2017

Update. Dealer replaced the DEF supply line to the DEF injector, part number 42492083 to correct the low DEF pressure problem due to the line melting on the exhaust manifold from incorrect installation. I'm curious how that could have caused the initial code for the DEF heater control circuit. There isn't a photo in the part system for the tube and the service writer mentioned it might have an electrical connection as well but I find that hard to believe. Might have to take a look for myself out of curiosity.

On the way home from the dealer a few days ago it did some odd surging/bucking, way worse than anything I've experienced on the gen 1 diesel. It happened again this morning even worse after a cold start, bucking at part throttle and low to medium engine load a couple minutes into the drive.

No codes yet so I might give it a couple days before it heads back to the dealer again. Thought it could have been a really rough regen cycle but they ran it through a regen cycle and the engine wasn't even up to full operating temps.

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91794

· #11 · Nov 20, 2017

blackbird singing in the dead of night,
some queries about your car which we can temporarily name Bucky no-Dent.

- in which gear and at what speed did the after-cold-start bucking occur?
- did you try downshifting and/or slipping the clutch and/or shifting to neutral and idling to see if any of those things eliminated the bucking?
- during the bucking, how far was the go-pedal pushed in terms of percentage of its range? (what does part-throttle mean in this context?)

best regards...

/e

blackbird

Discussion Starter · #12 · Nov 20, 2017

Happened at about 35-50 mph, light acceleration in gear (both 4th and 5th), say rolling into ~25-35% throttle. I haven't had a chance to pull out the scan tool yet to see if there's anything pending. Not very fun doing drivability diagnostics on the brand new car but I haven't been super impressed by the selling dealer.

91794

· #13 · Nov 20, 2017

blackbird, your description sounds somewhat consistent with being in too high a gear at too low of a speed, which i understand can result in rough running especially when engine is cold.

but of course i don't really know. I am eager to find out the diagnosis and your choice whether to continue with the vehicle or just trade it for a ATS-V or a corvette.
i'm just a way-too-interested customer & driver - I'm not a pro/mechanic.
i'd be annoyed if my cruze diesel was giving problems due to an initial defect such as your car had.

Wow, bb, you had TWO Citation X-11s, 81 and 85.
You may be the only person in history to have bought TWO of those things! :|

blackbird

Discussion Starter · #14 · Nov 20, 2017

I've actually owned three X-11s at one point but still have those two sitting in storage. Although I really like the ATS-V coupe I'd probably have to sell my CTS-V so that isn't happening anytime soon.

Back to the Cruze, this isn't a problem with lugging the engine. It happens right around the engine's torque peak and I was in the suggested gear for the speed. I did downshift right after it happened the first time to give it a little more revs (north of 2k) and it still happened a few more times when rolling into the throttle. The diesel otherwise pulls perfectly fine and smooth once warmed up.

I'll keep the scan tool connected and logging to see if I can catch something. If it's hard to replicate, the dealer will have trouble verifying so I'll see how it goes the next couple days and take it back in after the holiday. They'll want to do their own diagnostics anyway so it's mostly for my curiosity.

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Cruz15

· #15 · Nov 21, 2017

Did you check the trans fluid level or the dealer at least? Should throw a code if its low, but maybe not until critically death low.
Maybe a sensor didnt get plugged back in correctly.?

blackbird

Discussion Starter · #16 · Nov 21, 2017

It's a manual trans and shifts fine. Since it didn't start doing this until the most recent repair they could have moved or touched something when were replacing the DEF feed line. Whatever it is the surging/bucking/momentary cutting out hasn't set an error code yet but in the morning I'm going to see if there's any pending codes.

I'm going to drive it a couple more days and maybe take a closer look over the holiday. The first time it happened which was immediately after leaving the dealer for the DEF line repair it was fairly minor. After putting a lot of miles on a first gen diesel, my immediate thought was it was doing a regen cycle. On the first gen cars at light load you can feel an ever so slight change in throttle and powertrain behavior on light load throttle tip-in.

It's only doing it on warmup and has been much worse on subsequent drive cycles when starting cold. I'm also fairly certain it isn't doing a regen under a minute after startup and before the engine has reached operating temp, and the fuel economy isn't taking a hit on the driver information center.

The other way to describe it for someone that's owned a lot of factory turbocharged vehicles would be if the turbo was over-boosting and/or the engine controller momentarily and suddenly opened the wastegate to cut boost. Watching what the manifold absolute pressure (MAP) sensor and boost pressure is doing is also on my list. Beyond that if I had to guess it seems like fueling or fueling timing is off.

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blackbird

Discussion Starter · #17 · Nov 28, 2017

Update 3. Car is back at the dealer and the same diesel tech that finally found the melted DEF supply line/harness confirmed he was able to replicate the hesitation/miss that's occurring after a cold start and was also able to tell it was still doing it slightly when warmed up. The service writer said the tech couldn't find any codes and tried to say that it might be due to the "wastegate" when cold.

I took that mean the tech thought it was the wategate (which is a bypass valve that controls how much exhaust gas flow over the turbocharger's turbine wheel, which controls how fast it spins and therefore how much boost it makes) was in closed loop, pre-programmed settings before the engine warmed up. I don't really buy that since it had perfect drivability for the few days I was driving it with the DEF after-treatment codes set. Come to think of it, I thought GM was using a variable geometry/variable vane turbo which would use a boost control solenoid but not a conventional wastegate flapper valve for primary boost control.

Over the last week I did get a chance to pull out the scan tool and do some high-speed data logging and was able to catch a couple of the hesitation events. It looks like the MAP sensor and fuel pressure were dropping/spiking downwards during a big hesitation event and the MAF was also dropping slightly. The service writer wanted to give my car back because "no codes, therefore nothing must be wrong" so I mentioned to the service writer that I'd just bring it back again and he reluctantly agreed to have the tech look at it again when cold and data log the sensor data.

While there's tons of great techs out there, unfortunately they don't get paid a lot for warranty work and therefore drivability problems that can't easily be traced to a bad part, check engine light, or service bulletin often don't get the attention and time needed to track down. I'll see what they say tomorrow. On a positive note, I did get a new Camaro SS for a service loaner. Or maybe that's not a positive. I can't see out of the darn thing and I swear they made the side mirrors smaller in the redesign.

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Rivergoer

· #18 · Jun 26, 2018

blackbird said:
Update 3. Car is back at the dealer and the same diesel tech that finally found the melted DEF supply line/harness confirmed he was able to replicate the hesitation/miss that's occurring after a cold start and was also able to tell it was still doing it slightly when warmed up. The service writer said the tech couldn't find any codes and tried to say that it might be due to the "wastegate" when cold.

I took that mean the tech thought it was the wategate (which is a bypass valve that controls how much exhaust gas flow over the turbocharger's turbine wheel, which controls how fast it spins and therefore how much boost it makes) was in closed loop, pre-programmed settings before the engine warmed up. I don't really buy that since it had perfect drivability for the few days I was driving it with the DEF after-treatment codes set. Come to think of it, I thought GM was using a variable geometry/variable vane turbo which would use a boost control solenoid but not a conventional wastegate flapper valve for primary boost control.

Over the last week I did get a chance to pull out the scan tool and do some high-speed data logging and was able to catch a couple of the hesitation events. It looks like the MAP sensor and fuel pressure were dropping/spiking downwards during a big hesitation event and the MAF was also dropping slightly. The service writer wanted to give my car back because "no codes, therefore nothing must be wrong" so I mentioned to the service writer that I'd just bring it back again and he reluctantly agreed to have the tech look at it again when cold and data log the sensor data.

While there's tons of great techs out there, unfortunately they don't get paid a lot for warranty work and therefore drivability problems that can't easily be traced to a bad part, check engine light, or service bulletin often don't get the attention and time needed to track down. I'll see what they say tomorrow. On a positive note, I did get a new Camaro SS for a service loaner. Or maybe that's not a positive. I can't see out of the darn thing and I swear they made the side mirrors smaller in the redesign.

Just curious...results on the hesitation event diagnostics???

blackbird

Discussion Starter · #19 · Jun 27, 2018

Dealer looked at it four or five times, confirmed it was doing it, but still says it's normal, the turbo wastegate, etc. It's gotten much worse now and does it every drive, all the time, hot and cold, continually when transitioning into the throttle. It's also been throwing a low vacuum code and a check engine light during severe events that goes away after a few drive cycles.

Just a guess, it's almost symptomatic of a MAP or MAF sensor with a dead spot. I gave GM a final attempt repair notice according to my state law, they couldn't coordinate with the dealer to get a regional field rep in to look at the car, so it's now with a lemon law lawyer. If there's no progress on that front I'll likely take it to a different dealer I trust or spend some time myself going over the car.

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