Bottom Line
Maintenance Q&A
Battling blinking lights, blown circuits and bad batteries

By Paul Abelson, senior technical editor

Q. I have a 2004 Volvo VN. The aerodynamic headlights keep burning out every month or two. At first I took the old bulb to the truck stop and bought a replacement. Then a friend with the same problem told me to go to a discount car parts store where I got the same bulb for a lot less. That didn’t help other than to save me some money.

Because of CSA, I don’t want to have one go out on the road, so I went to my Volvo dealer just in case it was a wiring problem. They checked the wiring and couldn’t find anything wrong, but they still charged me a hefty diagnostics fee. Can you help?

A. I can’t help with the diagnostics fee. Remember, your truck took up a service bay and a technician’s time, so even if the search was unsuccessful the dealer needs to cover his costs. If you were in the market for a newer truck or were a regular customer, you might have some leverage with the dealer. But I digress; back to the bulb.

Most likely, you are replacing the bulb with an incorrect part.

Two bulbs are visually identical: the 9004 and 9007. The same sockets fit but the filament and wiring are different. The 9004 has a transverse or crosswise filament, while the 9007 has an axial filament. The 9004 has a ground wire where the 9007 high beam is, and the 9004 high beam is where the 9007’s low beam connects, The two bulbs have different notches in their mounting bases, but strong hands can, and sometimes do, force a fit. The Volvo uses 9007s, while Mack uses 9004s. With the sister companies sharing dealers, it’s easy for a parts counter attendant to get the wrong bulb.

A forced fit can cause the bulb to vibrate when not seated properly, and vibration shortens bulb life.

Q. Occasionally, most often when it rains or snows, my Peterbilt’s circuit breaker pops. It’s the one for my lights, which sets up a dangerous situation – especially at night. It could get me a CSA violation. When I reset it, sometimes it works and sometimes it pops out again. I’ve changed circuit breakers and it doesn’t help. It’s just with the lighting circuit.

A. In most states, license plates are required on the front of the tractor and the rear of the trailer. In a few states, they are mandated for the rear of the tractor. That’s why all new tractors have rear license plate lights.

The running lights and the license plate light are on the same parallel circuit. One blown bulb will not affect the others, but a short at the license plate lamp assembly will pop the breaker for all clearance/marker lamps.

Because it is difficult to check when you’re hooked to a trailer and it’s usually not needed, the license plate lamp is often overlooked.

The bulb may have burned out, or more likely the lamp assembly has cracked or corroded. Water and salt spray are probably getting into the housing. When water and salt combine, they can create a short circuit. Until a few years ago, white LEDs were not available, and many tractors with LED lighting packages still had incandescent license plate lamps.

The bulb may not be burned out. If the socket assembly is corroded, the bulb may create intermittent shorts. That’s why the breaker may work sometimes but not all the time. This may happen with any lamp on the circuit, but the others are visible. The hidden license plate lamp is usually the culprit.

The fix is easy. If you need the lamp for a rear plate, replace the wiring and socket with a sealed assembly or LED. If you don’t need it, rewire to take the socket out of the circuit. Don’t forget to waterproof your splices with sealed connectors and heat shrink tubing.

Q. The absorbed glass mat (AGM) batteries keep failing in my 2010 Cascadia. They are expensive. Freightliner stood behind them so far, but I’ve been told that this was the last time.   

Can I change to regular batteries? Will they last longer? I was using the AGM batteries with an electric air conditioner. Could that have shortened the battery life?

A. There are many advantages in using 12-volt air conditioning for idle reduction, but that’s a topic for a different day. As for your question about the air conditioner shortening battery life, it’s an insignificant factor. In fact, AGMs are made to power idle-reduction equipment.

Other things are shortening battery life in Cascadias.

Some fleets have had good experiences with conventional flooded cell lead acid batteries, but that defeats the original purpose. Freightliner is aware of the problem. It has been a discussion topic on TMC’s LinkedIn pages. You should have a strong negotiating position to extend your warranty with your dealer.

Carl Tapp, one of my Maintenance Q&A brain trust advisers, believes it’s a heat-related problem. In the Cascadia, the battery box is open to the engine, where it gets a great deal of heat. Aerodynamic fairings cover the sides of the box, limiting cooling air flow. Heat is also generated from overcharging.

AGM batteries are very sensitive to charging voltage. Different makes have different maximums, ranging from 14.2 to 14.6 volts. If the maximum is exceeded, internal temperature increases and the batteries are cooked. Continuing to apply voltage after the batteries are fully charged can also destroy them.

“Smart” chargers are required.

In your DD15 engine, the alternator is very near the turbo charger. It lowers electrical resistance, allowing the alternator to generate more current. That can compound the problem.

We’ll let you know of any Freightliner actions or any information from TMC. Meanwhile, unless you can relocate your battery box to keep your AGMs cooler, switching to flooded-cell batteries may be your best bet. Work with your dealer to make sure you have enough amperage to crank your hard-to-start engine. LL