Tech Q&A – December

DEF Sensor Failures

Q: Our coach is a 45-foot 2019 Tiffin Allegro bus with only 12,000 miles on it. We were traveling through New Hampshire (24 miles from a scheduled campground stop) when the DEF (diesel exhaust fluid) light came on.

Knowing the tank was almost full, but unsure what to do, we stopped and put more in. The Check Engine light then came on and the coach would not go over 5 mph.

Of course, it was late Friday afternoon. We got towed to a trucking terminal. No one could check codes until Monday. The verdict was it needs a new part, which is unavailable. We were 500 miles from home and needed to be there that same day. Ugh.

The part is back-ordered for months. We were unhappy to have to leave a $500,000 coach and drive our dinghy vehicle home. We are very unhappy with Tiffin for not letting us know of this problem, which left us stranded on the interstate.

Patricia Briggs, via email

A: I’m sorry to hear of your plight. It has been reported that the power derate, which limits the coach to about 5 mph, can occur between 30 and 300 miles after the warning light comes on. This failure is becoming all too common.

The EPA requires diesel motorhomes built since 2016 to have a special sensor that detects the purity of the DEF in the tank. This was brought on by people trying to dilute the DEF with water, etc., to save money. DEF that meets ISO (International Organization for Standardization) 22241, the industry-recognized standard, is 67.5% deionized water and 32.5% urea.

The EPA requires the manufacturers to include engine software that derates (reduces) power if a bad sensor reading is detected. The computer cannot tell the difference if the DEF is bad, or the sensor is faulty. It is not Tiffin’s fault; the system is required by law, and other coach manufacturers are faced with the same problem.

From the information I have been able to find, Tiffin has had failures of both the DEF tank heads and sensors. Tiffin only installed the DEF systems made by Shaw Development in the Power Glide chassis, which is used under the Allegro Bus, Breeze, and two Phaeton models.

They are now on the sixth generation of sensors. Unfortunately, I have heard that this version is still having failures. These DEF sensors were required starting in 2016, but the 2018 and newer models seem to have the most failures.

Hopefully, the part for your coach will arrive soon. There are widespread backorders. I have heard that some mechanics have found a temporary workaround solution, which may or may not work in your case.

The DEF deteriorates over time. Motorhomes that sit in storage are especially prone to this problem, compared with commercial diesel trucks. Stale or contaminated DEF is drained out and the tank and head flushed with filtered or distilled water, then drained and refilled with fresh DEF. Again, no guarantees, but we’d like to hear from anyone who has success with this method.

In addition to dealing with the part failure, I recommend that affected owners file a complaint with the National Highway Safety Administration (NHTSA) online. A faulty part that causes the vehicle to only be able to drive at 5 mph is certainly a safety concern. If there are enough complaints, it may spur an investigation and recall on these components.

It also may not hurt, except financially, to buy two of the sensors in question for your rig, one they install after the failure and another to carry along for speeding up the repair next time.

GM V8 Valve Problems

Q: We have a 2019 GMC Sierra 1500 pickup with a 5.3-liter V8 engine. It only has about 20,000 miles on it and already has noisy valve lifters. We change the oil more often than the maintenance schedule calls for and use premium filters and synthetic oil. Is there anything we should be doing? Have you heard of any problems like this?

Smith, Dallas, Texas

A: Unfortunately, yes I have. Valve lifter problems are quite common in L84 5.3-liter V8 and L87 6.2-liter V8 gasoline engines like you have. It’s a manufacturing defect.

These are used in 2019 and newer Chevy 1500 Silverado, Suburban, and Tahoe models, along with the GMC Sierra 1500 pickups and Yukons, plus the Cadillac Escalade. GM pickups and SUVs with either the L84 or L87 can also develop a misfire condition due to bent pushrods and collapsed or damaged lifters.

Along with the lifter problems, there have been valve spring failures in recent 6.2-liter V8 engines, including L87, LT1, LT2, and LT4. There was a service bulletin dated September 2020 addressing this. The bulletin indicates that affected V8 engines may trigger a service engine lamp, combined with a misfire and engine noise, caused by faulty valve springs.

Other GM V8 engines, including the L82, L84, and L8T (used in 2500 and 3500 trucks) are included in the bulletin. Repairs of these problems are covered under warranty.

Coiled Cord Conundrum

Q: I see a lot of RVers coil their 30- or 50-amp power cords in nice coils, either in containers or on the ground after hooking up to shore power. You might want to check with an electrical engineer on how Faraday’s Law regarding coiled wire and how EMF fields affect that practice.

Are they unintentionally creating a condition that could possibly cause damage to the electrical systems of their rigs, especially because so many use electronics to control a lot of functions? Just a suggestion. Suppressors are not 100%.

John Lieber, via email

A: Faraday found that electrical wires coiled around a moving central magnetic core could induce electricity. Technically, there is a magnetic field around any wire with AC or DC current flowing in it. So, a coiled power cord could create weak electromagnetic fields (EMF), but in the real world, the amount of EMF generated is negligible.

There is no center core of ferrous metal or a magnet (unlike a Faraday coil). Modern RV electric cables are designed to reduce or eliminate this type of problem. The wires inside most cables are wrapped in a spiral pattern.

This not only makes the cable more flexible but also reduces magnetic induction. The older parallel-style cords probably created more EMF than the new three- or four-wire cords. In fact, I’ve never heard of an instance where EMF generated by a coiled RV power cord has caused a detectable problem.

Overheating wire due to insufficient cooling is a more serious problem. When a cord is carrying near maximum current, it is best not to have it tightly coiled and/or in hot sunlight. You can feel if the surface temperature is hot to the touch.

If any readers have a substantiated instance of a coiled power cord creating a significant problem, I’d like to hear about it. Also, if anyone has a gauss meter (which measures magnetic field) I’d appreciate it if they would test their power cord under load and report back.

Low Flow on City Water

Q: Thank you for all the informative articles in RV Magazine. We have a 2017 Keystone Raptor 355TS toy hauler. The RV’s freshwater fill and city-water connection (same connection) both have very low flow (less than 2 gallons a minute). However, when running on the freshwater pump (no city water connection), there’s an adequate/expected continuous flow (I believe it has a 4 GPM pump).

I suspect the city-water check valve to be the culprit, as I’ve already ruled out pressure regulators, filters, etc., upstream/external from the connection. There seems to be more than adequate pressure and flow to the city water connection.

Furthermore, it has an approximately 2-gallon accumulator tank that came with the freshwater pump, and you can always tell when the tank empties and you are left with the reduced “true” flow of the city-water connection (until the tank recharges again).

Although the check valve doesn’t leak (when no city water connection is present and pressurized by the freshwater pump), I wonder if replacing it with a more “high-flow” check valve would be your suggestion?

Kevin Allen, via email

A: Yes, I think you’ve nailed the culprit. It pretty much has to be the check valve restricting flow. I suggest something like the Valterra P23415LF brass ½-inch check valve and backflow preventer (1/2-inch MPT inlet by 1/2-inch MPT outlet).

They allow water to only flow one way and can be used on an RV hot water heater, water pump, or city water fill. You can find it here. 

Parking and Backing an RV

Q: My husband and I enjoy reading your articles very much. We now have a 2019 Keystone Cougar 366RDS and have been RV owners for 21 years. I would like to know if there are hand signals to use to assist my hubby when backing our RV.

My husband has hearing difficulties, and I don’t want to be yelling in the campground as we place the RV in its lot. We do have a camera on the back of the rig, which has helped immensely, but I still need to give directions to fine-tune our position.

Mary Rosenquist, Fort Wayne, Indiana

A: Safety first. The driver should walk completely around the coach to become familiar with obstacles before backing up any significant distance. Decide where to park to allow space for slideout rooms and awnings. Also, determine where you need to park so that sewage and water lines and power cables are accessible within distance for easy hookup.

Of course, motorhomes towing dinghy vehicles must unhitch before backing. The spotter should also look for all obstacles, including curbs, overhead obstructions such as wires and tree branches, and detritus such as broken glass, etc., which might puncture tires.

Always stay in view of the driver and never get in a position where you could get hit or run over by the RV. Agree on hand signals in advance; some of the online videos use different signals. In addition to hand signals, I recommend using a pair of inexpensive walkie-talkies such as GMRS units to quickly communicate about items not readily covered by hand signals.

There are some very good instructional videos online that cover this subject. Here’s a great example.

Upgrading From 30-Amp to 50-Amp Service

Q: We have a 2016 Coachmen Pursuit 29SB motorhome that we purchased new in 2016. At that time, we were new to the motorhome arena and did not research as much as we should have before we purchased. Our unit has one air conditioner and 30-amp electrical service.

The Pursuit also has a small black tank as well as a small refrigerator. We thought about trading it in and getting a new motorhome, but after all, we have already done to our unit (and have gotten most of the bugs out of it as well as the cost) we do not want to take that path.

The main thing we want to do first is upgrade from 30-amp to 50-amp service and add another air conditioner in our bedroom. What is the best and safest method to upgrade to 50 amps?

Tom Pahula, via email

A: Having the electrical system changed over by an RV shop or electrician can be quite costly, perhaps more than $2,000 for parts and labor. It entails changing the power panel out, along with the heavier power cord and perhaps the power converter.

I recommend having a qualified electrician do it for safety, as you mention in your priorities. However, if you aren’t a heavy user and haven’t exceeded your 30-amp service by using a large amount of power, and just want to add another air conditioner I have a possibly simpler solution.

Add a second power cord, this one rated for 20 amps with a 20-amp plug, which can power only the rear air conditioner. That would be far less expensive and a simpler solution. You can plug both cables into the respective 20- and 30-amp outlets on the campground power post.

There are also a number of lower-current-draw air conditioners entering the RV market. Check around and you may find an A/C that’s a perfect fit for your lower-available-power needs.

Roof Vent Cover Replacement

Q: Our fifth-wheel is a 2014 Keystone Cougar High Country 299RKS. We noticed that the cover on the exhaust fan in the bathroom has a quarter-size hole in it after a hailstorm. We put duct tape over the hole for now. Is the exhaust fan cover easy to replace, and does it have to be replaced with a specific one for our trailer or are they universal?

Vickie Rogers, via email

A: The vent covers are fairly universal, but I have found a few variations. Therefore, I recommend that you wait until the weather is dry and take the old cover off and bring it with you to match up at the RV shop. Removal and installation are easy. Once you get up on the roof, you can see how they attach.

Lithium Batteries

Q: First let me say that I am so glad Tech Q&A has returned. Anyway, not mentioning the lithium battery option for “Baffled by Batteries” (August issue) was not good. Lithium batteries can deliver more amp hours (Ah) without ruining the battery than lead-acid batteries, they are lighter, take less space, require no venting, and yes, they are expensive.

However, if you purchase one with a good warranty, it easily recovers its purchase price before the warranty expires while enjoying all the other benefits. Regardless of whether you agree with my assessment of lithium being the best option, you should have at least mentioned them as an alternative.

Gary Fanta, via email

A: Thanks for the kind words regarding this column. Perhaps I should have mentioned lithium batteries, so I will here at your request. I agree that they have many advantages over conventional lead-acid batteries. The main disadvantages that keep them out of mainstream use are their high cost, poor low-temperature performance, the danger of thermal runaways in some instances, and special charging needs.

For example, a lithium battery with a 100 Ah rating is typically more than $1,000. Many RVers install two to four 100-Ah batteries, so the cost would be more than $4,000. I hope that prices come down, but demand for lithium batteries is increasing, and Afghanistan has the world’s largest deposits of lithium, which may drive the price up.

Engine-Starting Battery Goes Dead—Tip

Q: We have a travel trailer, and I was reading your answer to the question about the engine-starting battery going dead (August issue) after a couple of days. I would look at the possibility of a bad diode in the alternator.

It can allow the current to drain back through the alternator and drain the battery. One symptom of a bad diode is the alternator putting out less than 12 volts when it should put out about 14 volts. Just a thought.

George Thaxton, Stamford, Texas

A: Yes, a failed alternator diode certainly could cause the battery to discharge, and owners should consider this. Thanks for this; it is helpful, useful information for readers.

However, the reason I didn’t include it in my answer was that a diode failure would also illuminate the charging warning light (which typically is an icon shaped like a battery), and there was no mention of that in the letter.

---

A member of the Good Sam family since 1988, Ken Freund has been helping readers better understand their RVs for more than 30 years. Throughout his career, he has been a service manager, technician, shop owner, an ASE Certified Master Technician, an instructor of the California Smog Check Program, and author of Haynes Repair Manuals.