05 Legacy Speedometer Suddenly Under by 15%

[mpower36]

2005 Legacy 2.5i manual transmission with 177k miles on it.  The speedometer suddenly started reading 15% under speed.  I've had this car for 5 years and had no problems with the speedo.  It has 205/55R16 standard size tires and was fine last week.  This week, at 60 mph per GPS, the speedo reads 51 mph.  At 55 mph per GPS, the speedo reads 47 mph.  I checked this with an OBDII tool and the OBDII reads the same as the speedo, so it's not the gauge itself.  So the car is displaying 85% of the actual speed.

The car has a CEL on, BRAKE light, and ABS light.  The OBDII scan only says P0457, loose gas cap.  Clearing the code has no effect.

Any ideas why this happened and how to correct it?

[mpower36]

A little new information that occurred to me... 2 weeks ago I changed the LF wheel hub, which required me to pull and reinstall the LF speed sensor. 1 week ago, I replaced the LFOB CV boot, which also required me to pull and reinstall the LF speed sensor. Since the magnetic encoder is in the wheel hub, might it be possible that the new hub doesn't have the right number of teeth on the encoder? The new hub is a Detroit Axle 513303.

[heartless]

very possible

if you still have the old hub you could check that

 

[1 Lucky Texan]

did you get new tires?

[mpower36]

Tires are the same.  Unfortunately, I threw away the old hub.  I plan to call Detroit axle on Monday to ask the difference between a 513303 and a 513220.  Maybe it's just the number of N/S poles in the encoder.

[mpower36]

ISSUE RESOLVED!

When I bought this 513303 hub from Detroit Axle, it came in a 2-pack.  I spoke with Martin at Detroit Axle customer service.  He told me his system shows a 513303 and 513220 hub are interchangeable.  He said I may have a damaged part, and he would ship me another 513303.  I asked him to send me (2) 513220s since the 513303 isn't working.  He agreed to send it. 

While waiting for the parts to arrive, I bought this magnetic field viewing film from Amazon for $18.99.
https://www.amazon.com/dp/B0BCFM83XB?ref=ppx_yo2ov_dt_b_product_details&th=1

When the film arrived, I checked the new 513303 hub from the box and it has 96 magnets in the encoder.

When the new hubs arrived, I pulled the suspect one off the car and found it to have 64 magnets in the encoder.  The hub on the left is the new 513303.  The one on the right is the suspect one.  You can easily see the difference.

 

I compared a 513220 and found the bearing housing to be a little different, but it had 96 magnets in the encoder.  The hub on the left is the 513303 from the car an the one on the right is the 513220.  See the straight sides on the 513220 vs the scalloped sides on the 513303.

 

So I installed a 513220 and took it for a ride.  ABS light is off and the speedometer is within 2 mph at 60 mph, which is within normal range according to what I've seen posted out there.

I will be returning the defective hub to Detroit Axle.  It's worth noting their customer service has been great.  They provided me 2 513220 hubs at no charge trusting me to return the 513303s and they sent a return shipping label.

I'll be checking every hub I install now with my new magnetic field film before I install it.

[nvu]

Great writeup mpower!  Those pictures really show the issue at hand.

[el_freddo]

Never heard of this magnetic field film before. Crazy! 

Cheers

Bennie