1992 Lexus SC 400 Speedometer and cruise control failure

Tiny
MONT.AUTO
  • MEMBER
  • 1992 LEXUS SC 400
  • V8
  • 2WD
  • AUTOMATIC
  • 127,000 MILES
While driving at 65 MPH on an interstate with the cruise control on, both the speedometer and the cruise control failed simultaneously. We installed a new sender (located ion the tail of the transmission) and installed a rebuilt gauge cluster. No luck with either/both. Could not get an electronic wave generator (which facilitates a car's motion) to move the speedometer's needle but, shorting the line briefly did get the needle to jump slightly.

So, what would you look for and where would you start the diagnostic process?

Have a good day.
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Monday, April 12th, 2010 AT 8:31 PM

7 Replies

Tiny
KHLOW2008
  • EXPERT
Hi mont. Auto,

Thank you for the donation.

Was the Vehicle Speed Sensor replaced new and of the correct type? Number of teeth and diameter of gear?

Remove the VSS and connect the wire harness. Turn ignition on and gt someone to help to turn the VSS by hand, does the speedmeter needle move?
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Tuesday, April 13th, 2010 AT 7:28 AM
Tiny
MONT.AUTO
  • MEMBER
Yes, the new VSS was identical.

Turning the new VSS by hand while it is connected to the wire harness and with the ignition on had no effect on the speedometer (that is, no movement of the needle).

Does this help?

Have a good day.
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Tuesday, April 13th, 2010 AT 9:15 PM
Tiny
KHLOW2008
  • EXPERT
Sorry for the delay in replying as notification was not received till now.

Perform the following and see if you an come up with anything.

SPEED SENSOR CIRCUIT

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 appropriate instrument cluster connector "A" terminal # 14 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 VSS. If speedometer/vehicle speed (4-pulse) signal and wiring harness are okay, replace circuit plate. If circuit operation is still incorrect, replace instrument cluster computer.

5. If speedometer/vehicle speed (4-pulse) signal and wiring harness are not okay, trouble shoot instrument cluster or repair wiring harness.


http://www.2carpros.com/forum/automotive_pictures/192750_InstrumentCluster92LexusSC400Fig06_1.jpg

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Saturday, April 17th, 2010 AT 7:52 AM
Tiny
MONT.AUTO
  • MEMBER
Thanks for your note. When the failure occurred while driving at highway speeds when the cruise control option was engaged, three items ceased to function simultaneously; namely, the cruise control, the speedometer and the odometer. At this point the cluster unit has been replaced with a rebuilt unit (no resulting change in operation) and the sender unit mounted at the rear end of the automatic transmission has been replaced with a new Lexus unit (no resulting change in operation).

So, how does one "Trouble Shoot" the odometer?

Have a good day.
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Saturday, April 17th, 2010 AT 11:27 PM
Tiny
KHLOW2008
  • EXPERT
If the speedometer and odometer is not working, then you can skip the checking odometer part.

As the VSS has been replaced, the next thing you need to check would be the wire connectivity from the VSS to the meter cluster and poser supply to the VSS.

Did you try to retrieve for trouble codes?
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Sunday, April 18th, 2010 AT 11:59 AM
Tiny
MONT.AUTO
  • MEMBER
No, did not attempt to retrieve trouble codes. Please advise proper procedure.
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Monday, April 19th, 2010 AT 1:05 AM
Tiny
KHLOW2008
  • EXPERT
At the VSS there are 3 wires.

1. Blue/Red = Speedometer, meter cluster.
2. Red = Ground
3. Yellow = 12 volt with ignition switch ON, ( Gauge fuse)

Test the continuity of Blue/Red and Red to meter cluster.

Red must have contiuity to ground.

Yellow must have battery voltage with ignition switch turned ON.

Trouble codes would only occur for Speed sensor # 2 which is for the transmission.
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Monday, April 19th, 2010 AT 8:10 AM

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