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  #1  
Old 21st March 2010
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Default Where is Speed Sensor ( Speedo Transducer)?

The speedo on my 1999, 9-3 automatic convert is acting up. For starters I want to check the connections at the transmission. Can anyone please tell me where the speedo sensor is located?
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Old 21st March 2010
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Originally Posted by SpongeBob View Post
The speedo on my 1999, 9-3 automatic convert is acting up. For starters I want to check the connections at the transmission. Can anyone please tell me where the speedo sensor is located?
Its either at the right or left side rear ABS "reader". There are in an environmentally unfriendly area(road salt, stones, debris,salt water, brake dust - the canary would never survive.)..
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Old 21st March 2010
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Its either at the right or left side rear ABS "reader". There are in an environmentally unfriendly area(road salt, stones, debris,salt water, brake dust - the canary would never survive.)..
Thanks - but where is the ABS reader? I thought the ABS readers( sensors) were at the wheel bearings - no?
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Old 21st March 2010
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They are on the front wheel hubs and perpendicular to the axles, which have a toothed wheel they monitor... Ron
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Old 21st March 2010
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They are on the front wheel hubs and perpendicular to the axles, which have a toothed wheel they monitor... Ron
Thanks - but where is the speedo sensor ?
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  #6  
Old 21st March 2010
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http://www.saabcentral.com/forums/sh...d.php?t=148020
The sensor is on a bracket, reading the reluctor which is integral with a spinning potion of the f or r axle.
http://www.saabcentral.com/forums/sh...ad.php?t=90971
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Old 21st March 2010
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Care to elaborate on what "acting up" means, it could be something else....
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Old 22nd March 2010
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Care to elaborate on what "acting up" means, it could be something else....
It seems that after a car wash or driving through a deep puddle of water my speedometer flickers and acts up and when the car dries up all is well again. I suspect that the problem could be a frayed cable which perhaps ground when wet, or a dirty connector from the Speedometer sensor. I assume that this sensor must be connected to either the auto trans or the diferential but I can't locate it.
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Old 22nd March 2010
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Look behind the wheel hubs. Find the cables and they connect to the sensors. I have seen some posts that say the left rear wheel sensor monitors the vehicle speed. Maybe these pictures will help:





... Ron
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Old 22nd March 2010
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Great info - thanks! I'm not 100% on this but I think that the ABS system and sensors don't have much to do with the speedometer. Do you know what gives the speedometer signal? I know that it doesn't connect to the rear wheels because when the front wheels spin, such as on ice, the speedometer shows their speed in MPH.
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  #11  
Old 22nd March 2010
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Great info - thanks! I'm not 100% on this but I think that the ABS system and sensors don't have much to do with the speedometer.They have everything to do with the speedometer, Sponge. All of the data from the sensors is entered into the ABS module; I imagine one of the 4 readings is picked up here and spent post-haste to the speedo. Do you know what gives the speedometer signal? I know that it doesn't connect to the rear wheels because when the front wheels spin, such as on ice, the speedometer shows their speed in MPH.
Strange, its supposed to be a signal from a rear wheel, as they are more true, accurate, and reliable.
There may be something strange amiss in the inner workings of the module.
But, how is this possible?
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  #12  
Old 22nd March 2010
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Quote:
Originally Posted by SpongeBob View Post
Great info - thanks! I'm not 100% on this but I think that the ABS system and sensors don't have much to do with the speedometer. Do you know what gives the speedometer signal? I know that it doesn't connect to the rear wheels because when the front wheels spin, such as on ice, the speedometer shows their speed in MPH.

They do, actually. It is the output from the ABS computer that gets sent to the speedo. Check your sensors, as others have said, and I bet you find your issue.

Terry
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  #13  
Old 22nd March 2010
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Originally Posted by tdrudd87 View Post
They do, actually. It is the output from the ABS computer that gets sent to the speedo. Check your sensors, as others have said, and I bet you find your issue.

Terry
OK - I was hoping that it was just a simple plug in to the transmission - but it seems that was just wishful thinking. ALSO I experimented by un-plugging the connector that fits on top of the trans. but it had nothing to do with the speedo which still worked. The only result of un-plugging this connector was that my check gearbox and ABS light came on - Thankfully when I re-plugged it the warning lights went off. I quess I will just have to avoid puddles -- joking.
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Old 22nd March 2010
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Quote:
Originally Posted by earthworm View Post
Strange, its supposed to be a signal from a rear wheel, as they are more true, accurate, and reliable.
There may be something strange amiss in the inner workings of the module.
But, how is this possible?
Well I'm learning -- but what is the explanation that when the drive wheels spin (such as on ice) the speedometer registers their speed?
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  #15  
Old 22nd March 2010
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Default I'm more confused now because -----

Just found the following on the Web which I cut and pasted below - This further confuses me --

Generally a non working speedo will be down to:-

1. Wire fallen off the signal generator ( sender ) on the top of the gearbox. It's down the back of the engine in a really difficult place to get at.
2. Aforesaid sender goosed.
3. Drive sprocket on same worn.
4. Drive gear in gearbox worn.

These are increasingly difficult to fix. No.1 just needs fumbling about and replacing the connector.

No.2 needs the sensor taking off. It is retained by a Torx bolt. ( I think a T27 ) This is very tight and needs a long extension to reach. I made one up from a length of 10mm rod with an old socket welded to the end. Also it's worth grinding the end of the Torx bit flat so that it locates fully into the bolt. Get it in place and give it a sharp tap to 'unfreeze' it, then it should come out. The sensor is just a press fit after you remove the little retaining plate. If you spin the gear you should see the speedo needle flicker. If the needle doesn't move then it's the sensor that's gone. I replaced the Torx bolt with a 10mm stainless hex bolt.

No.3 Examine the teeth on the gear. If they are very 'sharp' then they have probably worn such that they no longer engage. It's just a snap fit onto the sender unit. Cost less than £10 when I did one a few years ago.

Now even more confused: I also found the following which I cut and pasted below - I'm just going to live with the occassional speedo flicker.
  • The wheel speed from the wheel is an input to the TC/ABS module. From there, it is put on the bus to the main instrument unit(cluster), and the trionic module(engine control module). The abs lights are on correspondingly. The left rear sensor is the one responsible for vehicle speed. The AC voltage, from that sensor would need to be checked at the sensor, as well as resistance of the sensor.

Last edited by SpongeBob; 22nd March 2010 at 04:31 PM.
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Old 25th March 2010
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Default Yes you were correct and I was wrong.

Quote:
Originally Posted by earthworm View Post
Strange, its supposed to be a signal from a rear wheel, as they are more true, accurate, and reliable.
There may be something strange amiss in the inner workings of the module.
But, how is this possible?
Yes the signal does come from the drivers side rear wheel. I inspected the plugs at all connections to the wheels and discovered that one of the wires to the plug that goes to the L-rear wheel was damaged and just connected by a few strands. Now that I tugged on it the wire completely separated resulting in the ---speedo not working at all, ABS, Brake and check engine lights on. Until I find another plug that I can spice on, (other then no ABS braking system) will everything else work as it should or would something be damaged?
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  #17  
Old 25th March 2010
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According to the EPC, you may need to buy the hub in order to get the sensor.


Part Number 4839122
Description WHEEL HUB
Saab Suggested List $166.00
Quantity package?
Part Code (D = discontinued)
Superseded use this new number >click link
Core Charge $ 0.00

... Ron
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  #18  
Old 25th March 2010
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You know, SpongeBob, if the only time the speedo acts up is during the time the sensor is really wet, then I'd not do anything..
But, maybe you can improve its moisture resistance, somehow.
Some silastic?
Some of your garnered information is generic in nature, not specific to Saab or others.
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  #19  
Old 25th March 2010
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not meaning to thread jack...

where on a 97 2.3L 5spd does the speedo signal come from? same place? i was looking up parts and saw a seperate speed sensor for auto trans only.

Last edited by Tonto; 25th March 2010 at 09:08 PM.
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  #20  
Old 26th March 2010
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Default No - My wheel hub is fine.

The problem is that a wire is broken right at the male plug that connects to the female plug at the wheel sensor.
The question is:
Until I find another plug that I can spice on, (other then no ABS braking system) will everything else work as it should or would something be damaged?
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