Honda Repair: 97 honda accord check engine light, tacometer, honda accord ex

Question
Hello. We have a 97 honda accord ex with 59,000 miles.
Our check engine light went on so we took it in.  The mechanic ran the diagnostic and replaced the speed senor with a new one. After a half an hour drive, the check engine light went on again. Back to the mechanic. He ran another diagnostic and replaced the speed sensor again--in case the first was faulty. This time he let the car idle for an hour to make sure the light wouldn't go on. It didn't. Only, after a half hour of actual driving, it went on again! He's at a loss since the diagnostic always shows the problem is the speed sensor, which he's replaced twice. (He didn't charge us a penny for the second visit so we don't think he's scamming us.)
Incidentally, the tacometer doesn't work. It either sits at 0 or swings wildly.
What are the other possibilities for the check engine light?
Could it be related to the tacometer?
Thanks,
Jonathon

Answer
Jonathon:
Your mechanic may not be trying to scam you, but he is not properly diagnosing the problem. The diagnostic code may show where the problem is, but it will not necessarily show what is causing the problem. Chances are there was nothing wrong with the speed sensor in the first place. Something else has failed and is causing the speed sensor to malfunction and send the code back to the computer. You are correct that it may be related to the tachometer, that could be sending a failure back to the engine and the engine thinks the speed sensor is bad. You need to find another mechanic that will properly diagnosis what is wrong and fix it. Any one can start replacing parts until you find the right one, there are a lot of sensors in the car and it may not even be a sensor.
Good luck. Please let me know what the fix was and send in feedback.
Bill