Vehicle Speed Sensor Issue

[ChrisSyrus]

Hello all,

I'm having issues with my 97 Civic EX. So Bought the car a little while ago as a fixer had two codes, one for a bad o2 heater circuit (fixed) and an issue with VSS (p0500 or 501).

Upon inspection the VSS was corroded center post on both pig tail and VSS were gone. Car had a spare with it and I went to a scrap yard and cut one off another civic that had no corrosion and spliced it on.

Even after all of that there is still no speed read out at all. Is there any other recommended trouble shooting steps to take or any known good fixes. Please let me know!

Thanks!

 

[nd4sped]

Was the plastic gear head completely rounded off or missing? There is a composite gear on the differential that could be damaged too if the VSS and the circuit are good. To measure whether the VSS is putting out a signal you need an oscilloscope (analog/digital oscillating meter). If you get a signal then you have good contact with the internal gear, if not then the internal gear is not spinning the gear on the VSS.

This type of repair will require you to disassemble the transmission to remove the differential and replace the composite ring gear.

 

[ChrisSyrus]

Was the plastic gear head completely rounded off or missing? There is a composite gear on the differential that could be damaged too if the VSS and the circuit are good. To measure whether the VSS is putting out a signal you need an oscilloscope (analog/digital oscillating meter). If you get a signal then you have good contact with the internal gear, if not then the internal gear is not spinning the gear on the VSS.

This type of repair will require you to disassemble the transmission to remove the differential and replace the composite ring gear.

View attachment 26760

Would it be possible to leave it in the diff and using a voltmeter hand spin the tires and see if there a pulse by probing positive to ground? I don't have a fancy oscilloscope.

 

[nd4sped]

Most likely not because it needs to spin fast to generate the voltage.

Reed Switch-Type VSS

This sensor consists of a magnet and reed switch. In comparison to the Hall Effect sensor, a magnet, powered by a speedometer cable, is required to mechanically turn the reed switch on and off (approximately four times per one complete rotation of the magnet, which allows for calculation of pulse numbers per second and, therefore, to measure the vehicle speed). This is an active sensor that generates a voltage in response to continuous rotation of a magnet that has close contact with a probe. The voltage generated is directly proportional to the speed at which the magnet rotates.​

 

[HeX]

If I understood you correctly, the original speed sensor was heavily corroded (not burnt) both at the center pin and in the plug. You discarded the speed sensor for a spare provided by the previous owner, and now that you swapped in another plug the speed sensor still doesnt work.

If thats all correct, check to ensure the VSS pins are making good contact to the plug. They may just need a slight bending towards the contact points in the plug. Add some dielectric grease while youre at it.

 

[ChrisSyrus]

If I understood you correctly, the original speed sensor was heavily corroded (not burnt) both at the center pin and in the plug. You discarded the speed sensor for a spare provided by the previous owner, and now that you swapped in another plug the speed sensor still doesnt work.

If thats all correct, check to ensure the VSS pins are making good contact to the plug. They may just need a slight bending towards the contact points in the plug. Add some dielectric grease while youre at it.

I will try those. I still have the old sensor still. Never toss stuff until the job is done!

 

[HeX]

Good! I say clean it out and re-test it. You dont kbow for sure if the 2nd sensor functions to begin with.

 

[ChrisSyrus]

Good! I say clean it out and re-test it. You dont kbow for sure if the 2nd sensor functions to begin with.

Before the installation of sensor 2 I had checked for continuity. I had gotten response. Just attempted to read the corroded sensor and I get nothing even with spinning the shaft.

 

[ChrisSyrus]

Before the installation of sensor 2 I had checked for continuity. I had gotten response. Just attempted to read the corroded sensor and I get nothing even with spinning the shaft.

Update checked the current vss. Shows continuity on end pins (dont know if that helps). Also looking down to where the vss would contact somthing, Im not seeing what it makes with...

 

[nd4sped]

You may not see the internal gear from the hole as its offset. Good job diagnosing the VSS.

Try jacking up the front of the car and let the car idle. This will allow the front tires to roll and you should be able to measure voltage going up and down at the VSS.

 

[ChrisSyrus]

You may not see the internal gear from the hole as its offset. Good job diagnosing the VSS.

Ended up seeing that gear. Got out my good flashlight and basically mounted my car like some good ol after promp fun. Looks to be in good condition.

 

[nd4sped]

Ended up seeing that gear. Got out my good flashlight and basically mounted my car like some good ol after promp fun. Looks to be in good condition.

Good news, its really rare for the gear to get torn up unless fluid is really low. But I have seen them damaged before from foreign debris and low fluid. People don't realise they are plastic composite versus steel.

Since that looks good continue testing the VSS and circuit. Worst thing is you could have a bad speedometer, I posted the HSM for replacing one a few days ago in another thread for a similar issue.

 

[ChrisSyrus]

Hmmm another bad speedo? Is it common for these cars to chew through them? Luckily I have a car yard near by with an abundance of 97 civic. New England eats these cars up.

 

[ChrisSyrus]

Alright last update for a little. Made a discovery. Decided to bypass my instrument cluster by using live data off of my OBD II Scan tool. Jacked up one tire and spun the ever living hell out of the tire... And we have data!! Its giving me speed read outs, at this point would we all agree that the speedometer is at fault here? If yes I'll go harvest an instrument cluster or two and an extra speedo for diagnostic purposes.

 

[ChrisSyrus]

Alright last update for a little. Made a discovery. Decided to bypass my instrument cluster by using live data off of my OBD II Scan tool. Jacked up one tire and spun the ever living hell out of the tire... And we have data!! Its giving me speed read outs, at this point would we all agree that the speedometer is at fault here? If yes I'll go harvest an instrument cluster or two and an extra speedo for diagnostic purposes.

Here's the read out I got

 

[nd4sped]

Looks good to me. Go salvage a cluster.

 

[HeX]

Before you do that, inspect the cluster harness. Its possible the wiring is spliced somewhere or the pins arent making good connection. If youve had similar previous issues then you should look into it.

 

[ChrisSyrus]

Before you do that, inspect the cluster harness. Its possible the wiring is spliced somewhere or the pins arent making good connection. If youve had similar previous issues then you should look into it.

I look at that too. The last owner said that he had to change it out, still have the original speedometer that he switched out (had to match up the mileage). Any recommended ways to test speedometers for function and same for the cluster housing? I have all week to mess with this car and I really appreciate the insight you guys have on this issue!

 

[ChrisSyrus]

Final Update. Didn't need to change anything else. After getting it legal an back on the road. I took it out for its first drive, and the Speedometer and Odometer were fully operational. Thanks to all who helped out here!