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BACKYARD MECHANIC: Fuse problem is no quick fix

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2011 Toyota Camry for $19,999

2011 Toyota Camry

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QUESTION: I own a 1996 Toyota Camry DX and it’s a high miler but it’s been the most reliable and economical car I’ve ever driven until recently. It now has an intermittent electrical problem. The 10-amp gauge fuse blows when the car is put in gear. Sometimes the fuse will last for days and at other times it will blow two or three times in a day.

I have checked the wiring for breaks and possible grounding at wear points, drivers door, trunk lid and back up lights etc. and haven’t found and problems there.

When the 10-amp gauge fuse blows (behind the coin tray) the following stop working; all gauges, heater, A/C fan, rear window defogger, power locks and windows, the alternator stops charging and transmission doesn’t shift properly. Why would so many vital functions be controlled by a single 10-amp fuse and yet there’s a 20-amp fuse that only protects the wiring to the dome light? I’d be very thankful to hear your input on this.

ANSWER: The 10-amp “gauges” fuse on your car provides power to many control circuits, including the climate control, A/C compressor, daytime running lights, the rear defogger switch, back up lights and warnings such as the seatbelt chime. A short to ground at any one of these could be the fault and finding the problem is a process of elimination.

The most likely areas to check are the wiring for the window controls at the driver-door hinge area, the A/C compressor clutch wiring and the backup lights. Inspect for broken wires that could short inside the plastic wrap. The wiring may look good on the outside but be broken internally.

You could start to diagnose the problem by unplugging devices such as the daytime running light module, the A/C compressor clutch relay and backup lights at the control switch. If the fuse still blows, then these circuits are not the problem. If the fuse is good for a few days, then you know one of these circuits is the fault and you can continue the process one circuit at a time.

You can try unplugging other circuits in the same way to locate the faulty circuit. Once the circuit is identified, then a careful visual inspection of the wiring may locate the fault. If the wiring is OK, then one of the switches or control modules may be bad. Unfortunately, there is no quick way to locate an intermittent problem such as this.

As for the 20-amp fuse for the dome light, this fuse also provides power to the audio system and sunroof if equipped so it needs to be bigger to handle the higher current flowing through those circuits.

QUESTION: I have a 2010 Sante Fe. The control to turn on the air conditioning is on the same button as the fan blower. Sometimes in the winter when the heater is on, the air conditioning button gets accidentally pushed in and both the A/C and heat are on at the same time until it’s noticed and the A/C is turned off. It’s a poor design of the controls in my view. Is this something to be concerned about? Thanks.

ANSWER: The button to request the A/C operation is separate from the fan control on many vehicles but having it located on the fan control isn’t a problem. All A/C systems have a low-pressure sensor or switch on the refrigerant system. When outside temperatures drop to below about 4 C, the refrigerant contracts, the pressure in the system lowers and the compressor is turned off even if the controls on the dash are requesting A/C. Your heater will operate as normal.

If you had the vehicle parking in a heated area for a couple of hours or it sits idling on a warmer winter day, the under-hood heat may cause the A/C system pressures to rise enough for the compressor to turn on. Again, this isn’t a problem. The airflow system of your heater is designed to mix cold A/C air and hot heater air to regulate the interior temperature. With the temperature controls set to warm, you will have heat inside. When the compressor operates for a short period of time, it lubricates the seals in the compressor. As soon as under-hood temperatures drop, the compressor will be turned off.

Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists’ Association of Canada.


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