Mechanics

SPEEDOMETER IS NOT WORKING CORRECTLY

1994 Toyota Corolla

1994 Toyota Corolla 4 cyl Front Wheel Drive Manual 175000 miles

I have checked the voltage going to the speed sensor and it is reading voltage. I have checked the speed sensor by the Haynes manual and it is reading like the manual states. I have purchased a used instrument cluster and is still not working correctly. While the ignition is in the on position the speed needle bounces back and forth 60 to 20 or bounces all over the place. It has done this when the speed sensor is unplugged too. When I crank it the speedometer reads anywhere from 20 to 80 and as soon as I drive forward or backward it goes to 0 and as I increase speed it increases very fast. When I am running 60 it shows 70 to 85mph. Is it the ECM, bad speed sensor(even though it checks good), or instrument cluster? Thank you.
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Antman258
September 29, 2008.




Hi antman258,

What you have done and described has covered the possibility of faulty meter cluster and speed sesnor.

I would suggest checking for bad ground connections.
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KHLow2008
Oct 2, 2008.
I have looked for the ground. The service manual states that it is located on the right instrument panel brace and I do not see one. I did not know if you knew where it was.

Tiny
Antman258
Oct 2, 2008.
Hi antman258,

It should be on the left side of instrument panel. Brown colored wire. Terminal A8 and B10 from meter cluster. Use a wire to ground them and see if it solves the problem.

KHLow2008
Oct 2, 2008.
I have grounded the instrument cluster and still get erratic behavior from the speedometer and I replaced the speed sensor. I can't think of anything else it could be.

Tiny
Antman258
Feb 3, 2009.
Hi antman258,

Does the symptom for both the original meter cluster act exactly the same or are there variations?

KHLow2008
Feb 3, 2009.
The symptoms for the clusters are different. The original cluster would fluctuate as soon as the car was turned on. The car did not even move to read a speed. The newer one works sometimes but the speed is never correct. What I mean by works is that it increases when I increase speed and it decreases when I decrease speed but it is not correct. Other times it just stays at 0 and sometimes spikes all over the place.
Thank you for the quick reply

Tiny
Antman258
Feb 3, 2009.
Hi antman258,

I believe we have found the cause of the problem. Both the meter clusters are faulty as they react differently. Quite often erratic behaviour are due to bad contacts on the printed circuits, connectors or attaching screws.
Check the priinted circuit for contaminations, especially at the connectors.
Check circuit board for cold solders and if possible resolder them.
Unloosen attaching screws, clean the contact areas and retighten them. DO NOT use excessive force to avoid damaging the unit.

KHLow2008
Feb 3, 2009.

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