1991 Speedometer shows 5MPH while parked

[Ohjai]

My 91 with 76,000 miles shows 5 MPH while standing still.  When I start to move it indicates the proper sped.  It appears to be accurate.

With this reading I am unable to perform the Injector Balance Test because the car need to be stationary.

This appears to be from the instrument panel, the engine data shows 0 MPH.

Any Ideas?

Thanks 

Jim

Edited June 13, 2023 by Ohjai

[2seater]

Hmm, I know nothing about the Tech1 but is there a zero button or anything like that to essentially do a reset to start a session? I have seen that with some other sensors or indicators where the key on supplies potential on the circuit and I imagine it is some sort of electronic noise or feedback causing this. I just looked at my 90 and key on, and engine running, or not, it displays zero. Even though the displays look similar the 91 has a different ECM. Something new every day but no help😖

[Ohjai]

What is interesting is the Instrument reading is 5 MPH but the output from the Engine module is 0 (zero).  As soon as the car starts to move the speedo approaches toward zero and starts reading the actual speed.

 

I have been looking all over for the spot where I can zero that value, but I am beginning to think it is a parameter on the EEPROM.  I'm not sure I have the skill set or equipment to tackle that.  At one time I would have, I worked on all sorts of communication - navigation and electronic systems, but my eyes, memory, and steadiness of hand  are not what they once were.