2005 Vectra Voltmeter sometimes takes a dive when unloading parking brake?

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oldryder

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Still learning whats normal on my new to me DP.

Occasionally when unloading the parking brake the voltmeter will drop from it's normal 13+v. to below 10v. for about a second. Not sure why and especially not sure why it would only do it irregularly.

Alternator was just replaced and this event has occurred both before and after replacement.

mark in MN
 

Gary RV_Wizard

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Some more detail would help. Does "unloading the parking brake" mean engaging it or disengaging it? Is the engine running when this occurs? Are we talking about the chassis volt gauge on the dash or some other voltmeter?

Also, what year/make/model of DP is this (suggest you add that info to your signature line)?

Engaging or disengaging the park/emergency brake on a DP requires opening or closing air brake supply valves, so a shorted valve solenoid could cause a brief but major change in electrical load.
 

oldryder

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2005 Winnie Vectra. Engine running. chassis (dash) voltmeter. unloading means disengaging the parking brake.

Given it's intermittent seems like a problem that is eventually going to get worse. Do you agree?
If it is a failing solenoid would a failure leave me stuck unable to disengage the park brake?

will add coach details to sig line.

thx
mark in MN
 

John Canfield

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What's the situation with your chassis batteries, you have two of them and three house batteries. If you don't have any history of the battery age, replace them.
 

Journey

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After brain strain and days later found out that when I pushed in the parking brake yellow knob to release brakes it would rub up against the key switch next to it under the dash and pop the 30 amp ignition fuse.
 

oldryder

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thx for replies. what is the physical location of the "air control solenoids". coach is 2005 Winnie Vectra.
 

Gary RV_Wizard

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I don't know, but most of the air distribution system is under the front end. The brake treadle valves will be on the front fire wall, but I suspect the valve yo dump air from the main brake lines would be underneath.

There is an air system schematic in the topic linked below, but that doesn't show physical locations on the chassis.
 

oldryder

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Update: new batteries had no effect, problem still intermittent but getting worse as now the dash volt meter dives all the way to zero and stays there for a few seconds.

Dropped it at Winnie Service in Iowa yesterday for a couple of items inc. this. 1st several times the tech tried to make it happen it didn't. Gave it another try a few minutes later and it happened 2 or 3 times. Tech was perplexed as he said several times the parking brake circuit is all pneumatic.

I will report on the solution when I get the RV back. Hopefully it won't be expensive.
 

John Canfield

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The Multi Mode Data Controller (MMDC) probably drives the analog voltmeter. Is the gauge that's going to zero the analog meter or the digital voltmeter in the MMDC display?
 

oldryder

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Normal volts is approx 13.2v. very little variation except when disengaging the parking brake when it sometimes will drop all the way to zero and stay there for a second or two. This is what a volt meter would show if the circuit it was monitoring was subject to a dead short. However that should also pop a breaker somewhere and that hasn't happened.

This behavior started with a lesser drop from the usual 13.2v to something like 10 volts so whatever it is has gotten worse. problem has always been intermittent which makes it even more fun to troubleshoot.
 

John Canfield

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So what does the digital display indicate in the Freightliner Info Center for voltage?

Gary is correct, nowadays (going back 20 years) even the analog gauges are 'dummy' being controlled by the engine/powertrain module.
 

oldryder

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Thx for insights. Winnie Factory Service has it now and I expect they'll figure it out pretty quick as long as they can make it happen enough to do the troubleshooting.

I was not aware the dash gauges were anything other than the straight mechanical/analog gauges I grew up with. Makes me fell old ....
 

Gary RV_Wizard

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They make them look analog because us old timers like that, but most are fakes. The oil pressure sensor, for example, only reports OK/Not-OK, whereas the dash "gauge" shows a needle and a range of pressures. But it always shows around 55 psi, which is translated from "OK pressure". The other oil pressure reading is 0 psi, for Not OK. There is no value in between. Voltage readings aren't quite that simplistic - the ECM reports an actual voltage value - but loss of the voltage sense signal would still show as 0.
 
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