td1238

Hello. I'm wondering if a 1990 Honda Civic DX with cable-driven speedometer has a vehicle speed sensor. I hear mention of this, but am not sure where to look. Some say that it is in the speedometer, but they only point to the magnetic coupling device that magnetically couples the speedometer needle to the cable.

I am still trying to solve a problem that I am having in which the check engine light comes on when I drive downhill for any decent length of time. I said 10 seconds before, but it is actually 40. What happens is that I almost completely close the throttle and the O2 sensor reading goes up to the .80s, like it would for idle, but for some reason the computer doesn't like this, and throws an 'oxygen content' code (one light flash). Replaced the TPS. The MAP sensor seems to be working properly. Could be wrong. I've read that it should read about 1 volt at idle. It reads about .85 volts. It reads about 2.75 volts with the engine off, though, which is within range.

...So my only other guess is that there would be some device to tell the computer that the car is moving so that it doesn't go into 'idle mode' when the throttle is nearly closed. Of course when I completely close the throttle while the vehicle is moving, intake vacuum climbs high, and the computer shuts off the fuel, but if the throttle is held nearly closed so that the MAP sensor puts out nearly the same reading as it would at idle, the fuel mixture goes to a steady stoichiometric instead of fluctuating lean-rich, and then the code is thrown.

td1238

Sad. 130 views and not one response! I'm guessing that noone is responding because Hondas never break, and so noone even knows what I am talking about.

Guess I'll have to figure it out on my own, as always.

kellogg6316

yes there is a vehicle speed sensor with that generation. it has to be in the cluster and then signal is sent back to the ecu.

td1238

Well I found the answer for myself. There is a speed sensor in the speedo. It's a reed switch that opens and closes 4 times for 1 rotation of the speedo magnet. I tested it and it works well. There is also 4.55 volts across it when it is open. Not the cause of my problem. Found a hole in the diaphragm of the vacuum dashpot that kicks the throttle open when intake manifold vacuum drops low, as an effort to keep the engine from killing. Mended hole. Got much better control of idle with idle bypass, but repair did not solve my original problem.