Questions and Answers

Infiniti M30 Speedometer Reads High Q. Hi, I just bought a 1991 Infiniti M30. It has 82,000 miles on it. The problem I'm experiencing is that the speedometer reads 20 mph over the actual speed of the car. I checked it on the highway with my wife in our other car. Do you think it would be the speed sensor on the transmission or the speedometer itself?

I can get both from a local auto salvage yard but I would like to buy only one part. Please let me know what you think.

Thanks,
Eric

A. I would test the Vehicle Speed Sensor (VSS) first. Here's how to test it.

1. Remove the speed sensor, then connect a voltmeter to the terminals as shown in figure 1.
2. Rotate the speedometer pinion, the reading should be approximately 0.5 volts AC.

Figure 1

If the VSS checks out good, then you probably have a bad speedometer head.

Some early Infiniti M30s had a speedometer cable. If yours is one, then chances are the speedometer cable is going bad. You can try to lubricate it and see what happens. Disconnect it from the transmission and pull the center core out. Clean it well with lacquer thinner and inspect it carefully. Then get a big glob of Vaseline Petroleum Jelly® and put it in the palm of your hand.

Now feed the core back into the housing dragging it through the Vaseline Petroleum Jelly®. You will need to turn the core as it goes in. If it becomes very difficult, you may have a kink in the cable or a collapsed section of housing. In this case the best thing to do is replace the whole cable.

Reconnect the speedometer cable to the transmission and try it out. If the speedometer reads properly, you're done. If not, the speedometer head will probably need to be replaced.