2004 Diamond Da40 G1000 always running Hobbs meter

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jeremywpb
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2004 Diamond Da40 G1000 always running Hobbs meter

Post by jeremywpb »

I have a 2004 Diamond DA40 with a G1000. It has a hobbs meter which recently just started running all the time. It has been going on for about a month. I don't rent the plane so it is not a big deal, but at some point I know I will need to fix it.

Any ideas what could be causing this? One mechanic said if the hobbs was attached to a oil pressure switch and the switch was broken/ stuck it could run all the time. Does the DA40 come with Hobbs from the factory or is it installed later? Anyone else ever had this issue?

The battery is new and voltage is good.

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Steve
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Re: 2004 Diamond Da40 G1000 always running Hobbs meter

Post by Steve »

As far as I know, all the 2004s (and earlier models) came with the Hobbs from the factory. There is an oil pressure switch and a relay in the circuit. A stuck relay or low battery voltage, in addition to a bad pressure switch, could allow the Hobbs to run when the engine is off. The wiring diagram for the Hourmeter is DA4-9231-20-02 in Volume 3 of the Aircraft Maintenance Manual.

The relay is a real bugger to find - about the size of a sugar cube, it is buried in one of the big wiring bundles in the engine compartment.

Let us know what you find...

Steve

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Don
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Re: 2004 Diamond Da40 G1000 always running Hobbs meter

Post by Don »

All DA40's have a factory installed Hobbs meter. If you have a new battery and voltage is good, it sounds like you have a frozen relay latch that remains in the "ON" position.
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Kurt h
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Re: 2004 Diamond Da40 G1000 always running Hobbs meter

Post by Kurt h »

check that your overhead cabin light is off. if left on it drains the battery and then runs the Hobbs for some reason. Done it twice.
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Rich
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Re: 2004 Diamond Da40 G1000 always running Hobbs meter

Post by Rich »

I think the relay is a solid-state device. If so it's unclear what its failure state would be.

The hour meter circuit in the Lycoming version is constructed in an interesting way. One thing to check is the oil pressure switch and the wire to it. When the engine is not running, the pressure switch terminal should be grounded. If it isn't, the switch needs replacement. If the wire between the relay and the OP switch were to get disconnected or broken, the meter will run. Offhand I consider this a quite likely scenario, absent the low-voltage condition some have experienced. The latter is easy to check.
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