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Old 01-29-2005, 05:54 AM   #1
NRoberts
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Default Speedometer - how to test?

Iv just bought an OB, with no working Speedo. I was told it was the speed snesor (monted on gearbox), and replaced that without checking myself that it was faulty. Haveing replaced that I still ahve no working speedo/odemeter. having only just got the car my service manual is on order, but im keen to sort this fault meentime. Can anyone advise on testing the speedo?

If I take the instrument pannel out, disconnect the 3 wires (1 whire 2 black) which plug into the pcb behind the speedo, and put a multimeter across 2 of the wires, and get some pulsing while driving v sowly over a short distance(pulse 0.2-0.5 volts as far as i can tell from the multimeter). Not getting anything obviously meaningfull from the other wire. Does this indicate the correct siginal is getting to the PCB?

There appear to be about 5 connections between the PCB and the speedo/odemeter dial unit - I havent studied them in detail, but it would be good to be able to test them, so i can identify exactly what component is faulty.

If anyone dosnt know for the outback, but knows for the impreza i guess it may be similar

thanks - nathan
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Old 01-29-2005, 06:12 AM   #2
NWWagon
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One way to test to see if the actual indicator is bad is to take a battery (any should work) and attach one end the batter + terminal the other to one input pin of the gauge cluster for teh speedo./ Then take a potentiomitter (spelling?)/fader/adjustible resistor and hook it inline of the other side (-) and tie that into the other input of the gauge cluster. Then just turn the pot and see if you get any needle movement. Best advice I can give you.
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Old 01-29-2005, 07:15 AM   #3
Mulder
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^
No, don't do that.
The speedo does not work on simple DC, it uses pulses from the speed sensor. If you apply constant DC to it you may damage it. Besides the cluster has to be connected to the vehicle and properly powered for the gauges to work.
The easiest way to check it would be to use an OBDII scanner, or Delta Dash, and see if there is a speed signal being received by the ECU. Most likely there is, or you would have a check engine light. There should be someone in your area who can lend you a scanner, try your local forum.
If the speed signal shows up in the ECU but the speedo doesn't work, the problem is either the instrument itself or the wiring.
It would also help to post what year your car is. If it's a late model I hope you didn't order the print version of the service manual for a lot of $, because you can go to the Subaru tech website and download the whole thing for $20-
http://techinfo.subaru.com/html/index.jsp
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Old 01-29-2005, 09:12 AM   #4
NRoberts
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Mulder - are you talking about the input to the PCB, while perhaps NWWagon is taking about the dial itself (ie the output from the pcb?)
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Old 01-29-2005, 02:14 PM   #5
Mulder
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I think we're both talking about the same thing. He apparently is making the assumption that the speedo works with a simple DC signal, which it doesn't.
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Old 01-31-2005, 01:20 AM   #6
NWWagon
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oh... well good thing you jumped in there and saved the day mulder... man I feel like a dork. I was going off the knoladge I have from the aviation world wich most of the Indicators I work on use just a variable DC signal. My appologies.

-Matt
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