First, this is my first post. I joined because Iam impressed with most of the info and adviceI have found. Here is my issue:

I have a 93 DX with the D15B7. I know I need to replace the speedometer, based on my research through postings at this forum. Mine has always been 30 mph fast. But recently it has started acting eratic, then stops working, along with the odometer and tripometer.Sometimes it will start working again. This occurs atvarious speeds.

But, here is the odd part,just before this happens, I feel the A/T transmission downshift slightly. It feels like it drops out of overdrive. If I stop and accelerate, the transmission shifts normal, except for overdrive. When my speedometer starts working again, I can feel an upshift back into overdrive, and my odo/tripometer start rolling again.

Can the faulty speedometer cause this? I look forward to any input offered.

 

No, a faulty speedometer would not cause these problems.

1) Is your Check Engine Light ON? If so, retrieve the code because it may indicate a problem with the Vehicle Speed Sensor or its circuit.

2) Although I think it may be fine, check whether fuse #15 in the under-dash fuse relay box is blown.

 

Thanks for responding so quickly. My CEL does come on, usually shortly after the speedo starts to act up. I learned how to check and read the codes andthe #15 fuseby researching different post on this site earlier, and I will check these tomorrow. I neglected to mention before that when I close the thottle and coast, I can feel a slight engine surge, but nothing at idle or acceleration? Can a faulty VSS cause this problem?

 

Not sure, but this abnormality may be related to the A/T downshift issue mentioned in your first post. You may be experiencing these problems because the ECU uses the signal from the VSS to control not only engine performance but also A/T performance (see picture).

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