Adjusting speedometer

2493 Views 5 Replies 4 Participants Last post by Afty, Apr 12, 2002

aquiname

Discussion Starter · Apr 12, 2002

Is NOT possible

I asked jvitale (who has the service manual) to see if it can be done. Here's what he said:

jvitale wrote on 04-11-2002 06:48 PM:
According to the service manual, there is a sensor in the transmission that measures the vehicle speed and sends a signal to a computer chip in the speedometer. This chip sends another signal to a small electric motor that moves the speedometer needle. So there are no speedometer drive gears or speedo cables to play with. The manual does not say anything about being able to make adjustments. Looks to me like there is no way to alter the speedometer or odometer readings

It sounds like the computer system uses the current gear number (which corresponds to a hardcoded gear ratio), the engine RPM and a hardcoded wheel diameter to figure out what the current speed is.

The funny thing is that such a system should be very accurate, assuming the car is equipped with stock tires. Yet some people have reported that the speedometer can be quite inaccurate.

A.

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aquiname

Discussion Starter · #5 · Apr 12, 2002

Afty said:
I think it has the *potential* to be very accurate, but Nissan purposely makes it read a bit fast for our safety. Other car makers do this too; there was an article about it in C&D a few months ago. Interestingly, BMW had the least accurate speedometers in C&D's test.

Hmm, that gives me an idea. I could put on slightly larger tires (i was thinking 245/45-17, but I could do 245/50-17) which would get the speedo to work the way it should.

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