rxpclb

Can You Give Me Detailed Installation Instructions for the Speed Sensor in a '99 A6 quattro? I have the part. Not sure where it goes or how to install it. Thank in advance for your help AudiWorld. 😃

sounddude

Easy, requires no real tools.

Jack up the front and put it on stands.

Climb in

On the drivers side of the trans in front of the front axle shaft (Between the exhaust and the trans) you will see some wires.
The speed sensor is on there and it is the only square connection. (The main harness and multifunction switch are round)

Pushing the metal bar on the clip (then pulling the plastic) releases the electrical connection.

Push down on the long side of the old speed sensor. You will see that the new one has a little button on it. pushing down on the plastic to get the button out of the transmission hole will then allow you to turn the entire assembly until the long tab is clear of the tranny.

Pull up on the old speed sensor. It should easily remove.

Reverse the procedure.

It's a little hard to write down but if you don't understand any part just let me know.

rxpclb

Thanks. Do you think the speed sensor malfunction has anything to do with why my gas mileage has gone from 21-22 mpg to less than 10 mpg? I'm very frustrated. I'm at 190,000 miles (purchased in '05 @ 47K) and I'm having my 2nd Blauparts belt kit installed tomorrow. I love this car. It drives like a tank in the snow and rain, but if I can't get this mpg and speedometer thing fixed we're gonna be parting ways.

sounddude

Honestly no.

Speed sensor feeds the spedo so if your spedo is reading accurate it's likely good.

Also, if the speed sensor is bad you should quickly throw a tranny code and go Into limp mode. (Since the values of the input sensor and output sensor don't jive)

Do you know what codes you are throwing? 10mpg is terrible. I get 13 in limp mode. Since you say the spedo is malfunctioning I will reserve the option to say I don't know all the details of your problem and I've been wrong before.

rxpclb

I have noticed my transmission hasn't been shifting into a higher gear when I've expected it to. Instead of up shifting into a higher gear it will rev to a higher rpm (2,500-3000rpm) before shifting. I'm gonna put a fresh set of NGK plugs in (190,000 miles now. I think I replaced OEM plugs @ 95,000 so they're about due). Hopefully changing the speed sensor or spark plugs or a new timing belt kit will correct the mpg problem. I've got a check engine light that came on. I've had it come on a couple if times since the speedometer started acting funny. When I had it read the code that came up was invariable speed sensor. I'm not familiar with the limp mode transmission problem. What can you tell me about that?

sounddude

I'm not familiar with that code. Can you post the code number?

Timing belt won't affect MPG (unless it's not timed right on install.)

Limp mode means the tranny gets stuck in third gear. Only reverse and third. Real slow off the line but it will get you home. These cars can act weird. If you get a speed sensor code then you are on the right track to replace it. Paste all the codes you are getting then erase them all on see what pops back up.

When is the last time the transmission had a fresh filter/fluid? Have you checked the fluid level? Slipping shifts are not good.

4Driver4

And what codes are stored in the transmission control unit.

This car needs some diagnostic work. Changing the spark plugs to fix this problem is like wearing blue socks to make it rain.

rxpclb

P0501 was the only code that showed up when I had it read 2-3 weeks ago when this started. It first happened during the oppressive cold streak we had on the east coast. When the weather got above 25 degrees or so the light went off, but a few days ago while my son was driving the car the speedo problem and check engine light came on again.

I've serviced the transmission fluid twice (new fluid & filter). Once around 50,000 miles & again maybe in 2010 or 11 (not sure of the mileage). That's another thing I'll need to do... I've had the VW dealer do it both times previously because they've can get the vehicle up on the lift.

I agree, changing the spark plugs is a shot in the dark but it's about time to change them anyway. So I'll have my mechanic do it while he's doing the timing belt kit.

4Driver4

Is this reply to me? If so, it's out of place in the thread. Quote and reply button works best, please.

At least check the fluid level in the trans if you are confident about fluid quality.

That P code is a generic OBD engine code. You need to read transmission codes with VAG-COM.

sounddude

I agree with all he's said here. And after sleeping on it I'm going to take you down a quick road.

You are throwing a speed sensor code because your trans is slipping. The input speed sensor and output speed sensors don't jive so the trans computer is telling you one of two things. Either your speed sensor is bad or your trans is slipping. (In your case likely the latter) cancel te timing belt change. Find an audi mechanic with a vag or get one yourself and repost with your results. We can help but let me say that from what you've said, there is a 50% chance that your transmission needs to be replaced. I wouldn't throw money at a the engine until you get the trans working. Change the speed sensor and take it for a drive. It's likely you will still have the issue.

There are a many other things that can cause your tranny to slip like you are saying. Low fluid is #1 on my list. As well as low fluid pressure cause by old fluid gumming things up and a blocked filter preventing scavenging. A bad speed sensor would never make it to my list but it will eliminate that fault code as the real problem so give it a change.

By the way, what spedo problem??? I can't help but feel you are leaving out an important part of the puzzle. Spedo issue would support the sensor as a possibility.