Engine fuse blew when driving.

Tiny
THOMAS ESTABROOKS
  • MEMBER
  • 1998 CHRYSLER TOWN AND COUNTRY
  • 3.8L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 214,000 MILES
While driving to work my engine fuse blew. On getting it home I put another fuse in. The van started. Left to idle it was fine. When I stepped on the gas the fuse blew again. Trying another fuse I noticed the cruise control light came on just before the fuse blew again. Help!
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Monday, June 6th, 2016 AT 6:46 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
There is no way to diagnose this over a computer.

A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it's not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.

For intermittent problems like yours the bulb may be dim already. Watch what takes place when it gets bright. That is when the short is occurring. It could be due to the rocking of the engine when you shift between reverse and drive. It could be due to the body flexing when you drive over bumps in the road. The bulb limits current to a safe value when the short occurs, in this case about one amp. If the engine won't start with a brake light in the circuit, try a headlight bulb. The low beam filament will limit current to five amps, and the high beam filament will allow about six amps to flow.

In particular, look at the wiring harnesses to the oxygen sensors to see if one fell down onto hot exhaust parts. A wire with melted insulation can ground out intermittently and cause a short.
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Monday, June 6th, 2016 AT 7:29 PM
Tiny
THOMAS ESTABROOKS
  • MEMBER
Thank you very much. Is there a chance it could be the fuel filter? Or would that fuse blow first? Also do you think with the cruise control light coming on and could have something to do with that and if I disconnected the cruise control it would work?
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Tuesday, June 7th, 2016 AT 9:53 AM
Tiny
CARADIODOC
  • EXPERT
There is no fuse for the fuel filter. If you meant the fuel pump, that does get power through the automatic shutdown relay which also powers the ignition coils, injectors, and oxygen sensor heaters. It is the O2 sensor heater wires that cause this problem most often from the wiring harness falling down onto hot exhaust parts.

This same circuit also sends current back to the Engine Computer so it can verify that relay turned on when it was commanded to. The cruise control is run entirely through the Engine Computer too, so while the light you're seeing might be a dandy clue, It is highly unlikely it is the cause of the problem.
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Wednesday, June 8th, 2016 AT 9:43 PM

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