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TV Maven

Inaccurate Speedometer

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I have noticed in the past 8 months that I have owned my 2007 RX-350 that the speedometer is reading high by about 10%.

At 31 MPH the speedometer reads 34MPH and the radar signs show 31 and so does the external Magellan GPS.

This tracks well at 40 MPH also with the speedometer reading 44MPH and the GPS indicating 40 also.

At 60MPH the speedometer reads 65MPH and the GPS is indicating 60 MPH.

I had my FREE oil change yesterday, they also replaced the Variable Valve Timing Oil Hose and added a heat shield (no charge, replacement, warranty related) and drove the vehicle 9 miles and determined that the speedometer was within spec's.

They gave me a printed table with acceptable chassis dyno indications, ranging from errors of 15% @ 20mph to 5% at 100mph, with a check mark (added) at 60MPH showing a range of 60MPH to 64MPH as acceptable?

The next page indicated that the speed signal is present at the connector on the Combination Meter Assembly Wire Harness connector(C9 ?) and is checked with a combination meter which is used to check voltages between C9-1 and C9-18 and at 10 km/h should have a voltage change of 1V or less and 7.7 to 14V which should repeat 7 times per second. (so they need a sub-audio frequency meter, or a scope to show this waveform?)

The next section is related to inspecting the Tachometer (not required)

So, in summary, has anyone else noticed any high reading speedometer problems, and is there any way to correct it easily? Thank You

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The speedometers of most cars read a few mph faster than actual speed. The common wisdom is that car manufacturers do that to protect themselves from liability for speeding tickets. Plus, there is variation in the circumference of tires marketed as the same size that effect speedometer accuracy. The speedometer of my LS is off by several mph. I simply adjust my speed accordingly.

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I have noticed in the past 8 months that I have owned my 2007 RX-350 that the speedometer is reading high by about 10%.

At 31 MPH the speedometer reads 34MPH and the radar signs show 31 and so does the external Magellan GPS.

This tracks well at 40 MPH also with the speedometer reading 44MPH and the GPS indicating 40 also.

At 60MPH the speedometer reads 65MPH and the GPS is indicating 60 MPH.

I had my FREE oil change yesterday, they also replaced the Variable Valve Timing Oil Hose and added a heat shield (no charge, replacement, warranty related) and drove the vehicle 9 miles and determined that the speedometer was within spec's.

They gave me a printed table with acceptable chassis dyno indications, ranging from errors of 15% @ 20mph to 5% at 100mph, with a check mark (added) at 60MPH showing a range of 60MPH to 64MPH as acceptable?

The next page indicated that the speed signal is present at the connector on the Combination Meter Assembly Wire Harness connector(C9 ?) and is checked with a combination meter which is used to check voltages between C9-1 and C9-18 and at 10 km/h should have a voltage change of 1V or less and 7.7 to 14V which should repeat 7 times per second. (so they need a sub-audio frequency meter, or a scope to show this waveform?)

The next section is related to inspecting the Tachometer (not required)

So, in summary, has anyone else noticed any high reading speedometer problems, and is there any way to correct it easily? Thank You

I have a 09RX350, and I run the factory OEM Michelin Energy 18" tires at 32-33psi, i.e. nearly 10% above manufact.'s recommended 30 psi. My speedometer reads a constant +3mph from 55 to 85 mph.

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Yes, I believe they are factory tires, 6/32 remaining after 39,000 miles that were on a car from a three year lease.

They are NITTO NT850 PREMIUM 235/55/18 104R, so these are probably the OEM tires?

Bill

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Yes, I believe they are factory tires, 6/32 remaining after 39,000 miles that were on a car from a three year lease.

They are NITTO NT850 PREMIUM 235/55/18 104R, so these are probably the OEM tires?

Bill

I dont believe Nittos are a OEM tires for Lexus, amybe thats is the reason for the higher speed reading.

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Yes, I believe they are factory tires, 6/32 remaining after 39,000 miles that were on a car from a three year lease.

They are NITTO NT850 PREMIUM 235/55/18 104R, so these are probably the OEM tires?

Bill

I dont believe Nittos are a OEM tires for Lexus, amybe thats is the reason for the higher speed reading.

Yes, I believe Lexus current OEMs are either Michelin or Goodyear. My 08 came with the Goodyears, but I'm replacing them today with Michelins...$100 rebate for 4 tires at Discount Tire..rolleyes.gif

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Yes, I believe they are factory tires, 6/32 remaining after 39,000 miles that were on a car from a three year lease.

They are NITTO NT850 PREMIUM 235/55/18 104R, so these are probably the OEM tires?

Bill

I dont believe Nittos are a OEM tires for Lexus, amybe thats is the reason for the higher speed reading.

Yes, I believe Lexus current OEMs are either Michelin or Goodyear. My 08 came with the Goodyears, but I'm replacing them today with Michelins...$100 rebate for 4 tires at Discount Tire..rolleyes.gif

My 2008 is really going about 4 mph faster than the speedometer reading, and has done so since purchase. When brought to the dealer's attention, they said it was within factory tolerance. Mine came with Goodyear tires. They lasted about 24,000 miles. I had an RX 330 that came with Michelins that also had to be replaced at about 25,000 miles. The replacement tire was Yokohama Avid. These still had adequate tread when the car was traded at 60,000 miles. I put the same Yokohama Avid's on the 2008. They have only been on for 7,000 miles, so it's hard to say how they will last.

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