Novak Conversions Jeep Wrangler TJ radiator

Speedometer is freaking out

Viewing vehicle speed in the OBD2 live data stream with a code reader will tell you if the spikes are coming from the PCM, which will help determine the cause.

Edited to add: I said it again because it’s still relevant.
 
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sab said:
Viewing vehicle speed in the OBD2 live data stream with a code reader will tell you if the spikes are coming from the PCM, which will help determine the cause.

Edited to add: I said it again because it’s still relevant.
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Ya I don't have the reader you're talking about. I looked up what I think you're talking about on Amazon for like 70 bucks. You think that will tell me the info you talking about?

Screenshot_20240527_145417_Amazon Shopping.jpg
 
What's the speed showing through the ODB port? Got a code reader that can do live data? A Bluetooth ODB dongle and Torque Lite (free app) would do it.

-Mac
 
EROCK said:
Ya I don't have the reader you're talking about. I looked up what I think you're talking about on Amazon for like 70 bucks. You think that will tell me the info you talking about?

View attachment 530210
Click to expand...

The picture on their website shows vehicle speed graphed in real time, which is exactly what you need:
1716850672095.png


Yes, I think it will work.
 
Ok I got the ODB reader. The ECM is indeed freaking out with the insturment cluster speedo. Video attached below.
 
macleanflood said:
Time to pull the speedo gear and inspect the electrical connector on the back of the transfer case.

-Mac
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Did this further up in the post. Speedo gear is 3-4 years old and looks great. Put a new VSS on just because, did nothing. Keep in mind the speedo flips out with out the vehicle moving, while its parked as well. Even without the engine running. Though it is more frequent with the engine running.
 
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sab said:
Either there is a problem within the PCM, or the speedometer input to the PCM is corrupt, which could be mechanical (the drive or driven gears) or electrical (the harness).
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I have bypassed the harness to test it. Though I'm not sure that's a 100% test. It still does it, with the harness bypassed. The only thing left untouched is the PCM. Though it could possibly be the harness. As I had to leave it plugged in to the system as I was bypassing it to keep the jeep running. Other components get power from the same wire as the VSS
 
Novak Conversions Jeep Wrangler TJ radiator
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