JetsterDajet

2003 Civic LX - Manual Transmission

Problem: Speedometer/odometer doesn't work; CLI - OBDII: P0500

What I've done so far.

1. Easiest (yet most expensive) thing was to replace the Vehicle Speed Sensor. Dropped in a new one for $75 and it couldn't care less.

2. Check fuses (probably should have done this first). It's at this point I find an aftermarket Viper keyless entry/alarm system (poorly) installed under the dash. I mean... it's bad. Whatever did this needs to be slapped. I just bought this car, so everything is a surprise.

3. Verified all connections. Connection from VSS to cable. That cable to the ECU harness behind glove box. ECU harness to the fuse box. Gauge cluster connections as well.

4. Maybe my gauge cluster is jacked up? Self diagnostic is good.

5. Got my hands on the manufacturer's manual. It has a flow chart and part of it involves testing continuity and voltage at the 3-pin connector that plugs into the VSS. Bust out the mutimeter. Ground has continuity - check. One of the wires should have battery voltage - check. Last wire should be 5V or greater... reads out at 3.7V. Aha! This must be it. Right? The manual says "Repair short in the BLU/WHT wire between the VSS and the cruise control unit, or the ECM/PCM."

I go and check the voltage coming from the ECU to the harness (this is a WHT/BLU wire before it changes to a WHT/GRN before going to the VSS) It's... 3V? Weird. It picks up an extra 0.7 volts after it goes through the harness? Whatever. I check the output for that wire from the actual fuse box. 3V. Huh? The hell? What about the cruise control module? I... have no cruise control module. It's missing. Gone. Who knows where it is, but whoever had this car before me decided it was better off being somewhere else. I'm not sure if this is part of the reason I have low voltage coming out of the fuse box for the WHT/BLU speed sensor wire.

At this point I'm determined the shoddily installed aftermarket Viper system is causing either low voltage where it's spliced into wires under the dash or is otherwise interfering. I yank the whole system. No change.

I need a break from this -- I'm exhausted of sitting upside down under the dash all day. Am I on the right track? What else should I be checking?

Thanks in advance, guys.

ezone

Got a wiring diagram?

JetsterDajet

No, I haven't really been able to find anything definitive, I've just been tracing wires by sight or plugging/unplugging from the fuse box until I lose voltage. In this case, I'm measuring at the wiring harness behind the glove box. I see the WHT/GRN wire that comes in through the firewall. I know this goes to to the VSS. On the other side of the harness, it's corresponding wire is WHT/BLU. I take a reading from that pin in the harness and it's 3V. I plug it into the harness and take a reading from the VSS plug and it's 3.7V. I don't get it, but I'm pretty sure I'm measuring the right stuff...

If I had a good, detailed wiring diagram, that would be helpful.

JetsterDajet

Actually, I found one in the manual, I'll drop it here in a minute.

JetsterDajet

Here it is.

http://imgur.com/4bn91Jg

I see how that WHT/GRN to BLU/WHT wire iteracts with all of the EPS Control unit (not sure what that is) the ECM/PCM and Cruise Control Unit (which is missing). But, I'm not sure how they interact in terms of voltage...

ezone

First roll the car a couple feet while monitoring the voltage on the signal wire, since the VSS pulls the 5v either high or low as the car rolls along it may make a difference if it's sitting on a low.

Ok there may be several items that share the VSS signal.

One of my diagrams shows
Gauge cluster
ECM/PCM
Cruise control unit and/or actuator (depending on sedan or coupe)
Car Link if equipped

Basically you monitor the voltage on the wire in question then start disconnecting stuff to see what item might be pulling the signal voltage down.

If the cruise has been removed, is the connector exposed to weather? Water can cause problems as it can semi-bridge exposed circuits.
Do you have a sedan or a coupe?

.......And there are a couple of harness connectors to check, C101 and C102

C101 (20 terminal, gray) should be the one where the wire color changes from white/green to blue/white.

C102 (20 terminal, orange) is just behind that.
Terminals 11-14 in that connector look to be a set of junctions for this circuit connecting three blu/wht wires together, connecting the VSS to the ECM and then going off to the C101....SO I bet you could isolate right there, maybe remove the bridge and then use a paper clip to connect the VSS to just the ECM and see if you can get a speed reading on a scanner and if voltage comes back.


If you have a code reader, does it have the ability to display live operating data? Can you watch the VSS reading on it?

ezone

EPS is Electric Power Steering, which would have been on an Si. I think this diagram you have is not for your car......not sure if it is usable, can't tell how many misleading differences there may be.

JetsterDajet

For rolling the car (I'll probably just jack it up and have someone rotate the tire) and checking the voltage -- where should I be measuring and what am I looking for exactly? The manual details a similar procedure but I'm not sure what is good/bad and what each would mean.

This sounds good, I'll start here.

No, the connector is under the dash, just hanging there. Not exposed to any water.
It's a LX Sedan.

It's currently loaned out, but I'll get it back and check and see. Sounds useful.


It sounds like C101 is that "ECU harness" I was talking about -- I that's where I read 3V coming in on WHT/BLU.

I'm done with this for today as I'm exhausted and cut up my hands pretty good, need to let em' scab up. Tomorrow, I will check C102 and then proceed to disconnect stuff and see if I can get that voltage up. I'm definitely no electrical engineer, but in that diagram, looks like a good deal of the circuit goes through the cluster. Does that mean it's still possible the cluster could be bad? Do you think I should go through the trouble of finding a new Cruise Control Unit to put back in?

Thanks a lot ezone.

ezone

The VSS signal should switch 5v to 0v several times as the speed sensor rotates (IIRC 4x per sensor revolution?) that may translate to something completely different at the wheels though because of gear reduction in the VSS drive gears.

And if you jack it up just lift ONE front wheel off the ground and leave the trans in neutral, then slowly spin that tire while watching your meter.
Even with 3v showing on the signal wire, I'd expect the VSS would still pull it to zero several times as it spins.

================

Scrap all that. Your old sensor was probably good, just plug that one in to the harness and spin the gear. Watch the voltages.

In fact, check that 5v line with VSS unplugged, and leave it unplugged until you find the cause.

No on the cruise.

Since it should not be related to the cruise.......and the cluster is pretty easy to pull, I might just yank the gauge cluster out and unplug it just to see if the voltage on the VSS line comes back up.
Sounds easy in my mind LOL.

I think the 5v originates in the ECM, and the VSS pulls it to zero to create a square wave (0-5v) pattern, then all the other connected systems use that digital signal. Goal is to see if the ECM is sending 5v, and if something else on the circuit is pulling it down incorrectly.


Did this make sense?

JetsterDajet

Yes, I think so. I'll work on it tomorrow and report back.

JetsterDajet

Hells yes, my man! That bitch is working!

Unplugging from the fuse box until I found my draw was the way to go. It ended up being one of the connectors that plugs in behind the fuse box -- a huge pain to get to and unplug even with the fuse box dropped. Only problem is... I don't know what component I've unplugged. I just hope to god it isn't something that will throw a CIL -- but I'm sure it will be. I've looked up and down for a diagram of the fuse box that shows what each of the connector ports goes to and just can't find one. Some of the ports are labelled with letters, but this one doesn't seem to be. When looking at the back of the fuse box, it's in the middle row, all the way to the right. Above the bottom right marked, I believe, "X" or "Y".

The plan right now is to put everything back together and see if I'm still throwing a code -- if I am, run it and should give me a better idea of what's disconnected and thus what's drawing the VSS voltage down.

ezone

^Google Image Search^

Which one did you unplug?

JetsterDajet

Nice! Don't know why I couldn't find that.

It's "O", on the back.

ezone

Connector O
Terminal 11
Blu/wht wire goes to the cruise control unit connector terminal 12

Why something would be pulling the voltage down with no unit connected to it, I don't know...but I wonder if there is some contamination in the connector that could bridge circuits, or on the fusebox connector....or something else.....hmmm