1992 Lexus SC 400 Failure of cruise control and speedometer

mont.auto · Posted at Wed Nov 11, 2009 9:02 pm

Electrical problem
1992 Lexus SC 400 V8 Two Wheel Drive Automatic 121000 miles

While driving at highway speeds, cruise control failed along with speedometer. Tachometer still works. Replaced speed sensor at tail end of transmission and rebuild display cluster. Car runs fine save no speedometer and no cruise control. Suggestions?

KHLow2008 · Posted at Thu Nov 12, 2009 8:57 am

Hi mont.auto,

Thank you for the donation.

The problem should be with the Vehicle Speed Sensor.

Did you test the pulse from the VSS?
Did you check if the driven gear in trans housing is good?

mont.auto · Posted at Thu Nov 12, 2009 10:40 am

Installed a new speed sensor (eventhough the old one looked OK).

Did not check for pulse from the VSS. Please explain.

Have a good day.

KHLow2008 · Posted at Sun Nov 15, 2009 6:35 am

Sorry for the delay in replying.

VSS would not show any defet if it is faulty as it is electrically controlled and you need to test the pulse. One simple way is to check if the driving or driven gear is faulty.

Here are the diagnostic procedures for testing.

Speedometer/Vehicle Speed (4-Pulse) Signal Check

1 . Drive vehicle and check odometer operation. If odometer does not operate, trouble shoot odometer. If odometer operates properly, remove instrument cluster with wiring harness still attached. Go to next step.

2 . Turn ignition on. Connect voltmeter between instrument cluster connector terminal No 14, connector A, and ground.

Raise and support vehicle and rotate drive shaft.

3 . Voltage should fluctuate between zero volts to 5 volts (or more) per revolution of drive shaft. If voltage does not exist or does not fluctuate as indicated, go to step 5). If voltage fluctuates, go to next step.

4 . Check wiring harness between instrument cluster and cruise control ECU. If speedometer/vehicle speed (4-pulse) signal and wiring harness are okay, check and replace cruise control ECU. If speedometer/vehicle speed (4-pulse) signal and wiring harness are not okay, trouble shoot instrument cluster or repair wiring harness.

5 . Replace circuit plate. If circuit operation is correct, replace character plate. If circuit operation is still incorrect, replace instrument cluster computer.

© 2008 Mitchell Repair Information Co., LLC.

mont.auto · Posted at Sun Nov 15, 2009 6:34 pm

Thanks for your recent e-mail. As of this writing, we've installed a new speed sensor and the instrument cluster has been rebuilt by others. The symptoms of the problem are that the Odometer, Speedometer and Cruise Control are not working.

Your memo implied that we should pulse the VSS if the Odometer is working as if these items are all arranged in series with the Odometer being first, then the Speedometer and finally the Cruise Control. Is this correct?

Is yes, what is the proper procedure for trouble shooting the Odometer?

Have a good day.

KHLow2008 · Posted at Mon Nov 16, 2009 10:24 am

Odometer works when the VSS is sending signals so I would suggest you test the VSs signals and skip the odometer first.

One simple way to test is to remove the VSS and connect the wire harness. Get some one to turn the ignition switch ON and watch the speeedometer while you turn the VSS. If needle flickers, most probably the trans driving gear for the VSS is faulty.

mont.auto · Posted at Mon Nov 16, 2009 7:09 pm

OK. So, evidently the drive gear for the VSS is not attached directly to the output shaft (that is, gear teeth haven't been machined into the output shaft) . There is evidently some other power transfer mechanism involved. Yes?

If yes, what is the other mechanism? Generally, how does what powers the input gear of the VSS fail and how is it generally repaired?

Have a good day.

KHLow2008 · Posted at Fri Nov 20, 2009 6:19 am

Sorry for the delay in replying. I wonder why I am not getting any notification for this post though I have indicated that I should be notified.

The dirve gear is splined and installed onto the output shaft. If the gear is faulty, you would have to remove the end housing to get at it.Repair would depend on the fault.

The gear seldom fails though it can if the splines are damaged.

Did you do the test by turning the VSS?

Here is a diagram for testing the Odometer.

mont.auto · Posted at Fri Nov 20, 2009 11:56 pm

In response, have not tested by turning the VSS yet. Will advise. Have a good day.