Speedometer pointer falls below zero

Tiny
BLESSING EWOBOR
  • MEMBER
  • 2008 LEXUS RX 400H
  • 6 CYL
  • AUTOMATIC
  • 133,564 MILES
Hello, I am working on one Lexus hybrid vehicle, it has problem with its speedometer. The speedometer falls below zero, I opened the combination meter so that I can access the speedometer pointer (without removing any wire) with the engine running, I used my finger to push it back to zero as I removed my finger it was still at zero. Test drove the vehicle it responded properly, I thought it has worked. After parking the vehicle for some hours, the speedometer falls below zero again. The vehicle was test drive without adjusting it with my finger, it was observed that the pointer was moving gradually from where it was (below zero) when the vehicle is accelerating. This will give a false reading to the driver because it is not starting from zero. What could be the cause and how can it be fixed?
I drew a sketch of what I mean below.
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Monday, August 31st, 2020 AT 12:29 PM

7 Replies

Tiny
KASEKENNY1
  • EXPERT
I suspect the gearing in the cluster is the issue due to you being able to move it and it operates properly. However, we need to confirm that the speed sensor is sending the correct signal to the cluster. If it is then you need to replace the cluster.

Here is the testing that we need to run through and go from there. Thanks
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Tuesday, September 1st, 2020 AT 4:34 PM
Tiny
BLESSING EWOBOR
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Thank you very much.
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Tuesday, September 1st, 2020 AT 10:30 PM
Tiny
KASEKENNY1
  • EXPERT
You are welcome. Please keep us updated on what you find. Thanks.
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Wednesday, September 2nd, 2020 AT 7:06 PM
Tiny
BLESSING EWOBOR
  • MEMBER
Hello, the work of the testing equipment that are used in text you sent to me (techstream and oscilloscope), can't they be replaced by a scanner? You know that with the scanner one can view some graphs going to its live data of the control units.
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Wednesday, September 2nd, 2020 AT 11:19 PM
Tiny
KASEKENNY1
  • EXPERT
Yes. If your scan tool can graph these inputs then you can do that but that is only testing what the module is seeing from the sensor. The testing is having you test just the sensor which is why it has you back probe the connector and use the scope. I think if you use the scan tool and monitor the sensor input to the module that we will get the same basic information because if it is correct then the sensor, wiring and module are all good. If it is not correct then we don't know which one is the issue which is why it has you use the scope.

Does that make sense?
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Thursday, September 3rd, 2020 AT 5:41 PM
Tiny
BLESSING EWOBOR
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Yes, it makes sense.
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Thursday, September 3rd, 2020 AT 9:52 PM
Tiny
BLESSING EWOBOR
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Thank you.
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Friday, September 4th, 2020 AT 3:44 AM

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