sohcdamage

Car is a 93 civic ex coupe, swapped from auto to 5 spd. Keeps getting a cel for the vss and I can't figure out why. I've changed everything, the sensor itself is brand new, not used. I've replaced the plug-in, and tested the circuit.

After testing the circuit I got these results:

Black wire to body ground- continuity seemed fine 4.7 ohms

Yel/Blu wire to body ground- 12.08 volts, which is fine

Yel/Wht wire to body ground- 4.7 volts, which is close enough to be okay I think.

I didn't bother to jack the car up and spin the tire, the sensor is brand new, and i've tried many other used sensor with the same result.

So I got to the point in the flow chart where is said to either replace the sensor or to replace the speedometer. I tried another speedo but apparently it wasn't any good because about 10 minutes into the ride it quit working.

Now for the real funny part. I've noticed the last couple days that the cel only pops on if I downshift into a lower gear and let the rpm's come down under 1,500 or so. Which I find odd? Maybe a bad ecu? I ran into the same problem awhile back with the iat sensor and it turned out being the ecu.

I need some help deciphering what the car is trying to tell me and I think it's out of my hands now, i'm out of ideas.

Former User

Do you still measure ~5V on Yel/Wht wire terminal in the VSS connector if you unplug the connectors at the rear of the cluster?

Have you tested the wire running between the VSS connector and ECU for a short?

sohcdamage

I havent tested the Yel/Wht wire with the cluster unhooked, and what would that mean if I didn't have 5v?

I have not tested the wire running from the vss connector to the ecu for a short yet. I believe all I would have to do is loop the circuit with a voltmeter correct?

Gimme 5 minutes, i'm running out to test the connector with the cluster unhooked real quick.

Former User

Both the ECU and speedo supply 5 reference volts to the VSS, which in turn provides oscillating ground to generate the speed signal. If the ECU does not provide this reference voltage, then that's the problem. Note that this troubleshooting may be tricky as the problem appears to be intermittent. Try to do the voltage tests when the code is being thrown.

Short testing: Disconnect the VSS plug and the corresponding ECU plug and then test for continuity to body ground at either end.

sohcdamage

Ok, so I went out real fast and tested the Yel/Wht wire with the cluster unhooked, and was totally surprised.

I'm sure i'm not wrong, I checked 3 times, but it measured about 66v on the multimeter. Plugged everything back in and and it came back to 4.7v. So, i'm guessing it's not supposed to be 66v lol?

I'll try the test from the connector to the ecu tomorrow when the cel comes back on.

Thanks Ron, you da man!

Former User

Was the reading possibly 6.6V, 0.66V, or 66mV?

Also try the opposite test where you measure voltage at the Yel/Wht wire terminal in the VSS connector when the ECU connectors are unplugged but the gauge cluster plugs are still connected.

sohcdamage

I also have an extra ecu laying around, but it's an LS integra ecu, but maybe i'll throw that in and see what happens in the morning on the way to work.

This can't be that difficult. It's just a power, ground, and signal and it's kickin my butt all over the place.

Is it possible for me to hard-wire the 3 connections just to see if it's something from the speedo or ecu?

sohcdamage

Could've very well been yes, my multimeter does have an automatic setting so it adjusts to what your working with automatically. Sorry, all I had was a flashlight and couldn't really see what the scale was the meter was using, as I was holding it in my teeth.

sohcdamage

I also took the cruise control unit out the car completely just to make sure that there wasn't a short from the vss signal out thru the cruise control.

HondaPartsHero

http://www.techautorepairs.com/vss.html

Former User

You could still have a shorted wire anywhere in the Yel/Wht-to-Yel/Blu wire circuit that runs between the VSS and the ECU, speedo, cruise control, and auto tranny (are all AT wires removed?).

sohcdamage

No, all the auto wires are still there, but I did remove the interlock. The cruise unit is gone, along with the throttle cable/throttle adjustment box under hood. But maybe that circuit still has one connection somewhere. I thought by removing all of those things that circuit becomes obsolete?

I don't need those things, so I don't need them there anyway, i've already removed most of what I don't use.

sohcdamage

I just got the flow charts from all data and from what I can tell just by glancing at them, it comes down to a short or the ecm being bad again!

To me it makes more sense that it's the ecu, as the speedo works and everything else works, and if I take the car to 4,000 rpm and then down to 1,500 rpm with the throttle closed the cel comes on right away.

sohcdamage

Well, just got done checking the wires from the plug-ins at the passenger side strut tower all the way to the ecu and everything is ok.

Tomorrow i'm rippin the dash out and looking there..............

sohcdamage

Problem solved, shorted vss signal wire between the cluster and ecu.