Buddy of mine was in the car saying it felt like we were goin faster than the speedometer read. I told him "just feels like that bcus its a small car".... until I went by a Radar sign that registered me 8-10mph faster than the speedometer showed.

The day after that a cold front passed by and outside temps dropped from 80F to 45F. That morning the speedo read less than 5mph regardless of vehicle speed for the first 10mins and gradually registered higher as I drove. The longer I drove the higher it registered asthe car warmed up...but it still registered several mph slower than it should even fully warmed up.

After the cold front passed...I removed the instrument cluster and took the clear cover plate off then re-installed the cluster and turned the key on.Then I pulled the speedo needle off and manually adjusted it so the needleregisters about 7mphwhile the car is sitting still. It's closer to being accurate now...but...the amount it's offby varies and the lastcold front that blew in...it had almost no reading for again 10mins.

I'm not sure if the problem is with the Speed sensor on the trans...or the speedometer...or perhaps ECM output?

1.Does the speedometer sensor run through the ECM or connect directly from the trans to the speedo?
2.Are there 2 speed sensors? Perhaps 1 for the speedo and 1 for the ECM to act as a vehicle speed sensor (VSS)?
3. ORis there just 1 sensor that sends a signal to the ECM which reads the speed valueso the ECM can set parameters and then the ECM distributes it to the speedometer?

Am I looking at a bad trans sensor? speedometer? ecm output?

Thanks for all advice.
Dave

 

possibley just need a speedo cable?? it might be wore out and not working properly

 

Needle could be sticking for some reason.

 

Thanks for thesuggestions.

I don't think either applies here tho. There is no speedo cable I can find. The inst cluster pulls off and there are 3 electrical bulkhead connectors for the entire dash with no physical cable connected to the speedo so it's not a manual cable drive unit.

Sticky needle I had considered and I tested for free movement when I removed the cluster. The tach needle moves and returns freely but with the speedo there is a bit of resistance both in moving it upward manually and it returns slowly when released. This may be by design though since it's electrically driven and there is a return spring to stabilize the movement. I can't say since I don't have another unit for comparison.

Sticky needle theory might also not be validsince in cold weather (2 cold front events now with duplicate behavior) the speedo read 5mph or less for the first 5-10mins of operation until the vehicle was warmed up. If this was a physical sticking issue....the speedoparts would be cold and contracted in cold weather and should work more easily...notcauselow to no reading for 5-10mins.

I'm fairly certain this is an electrical issue...which brings me back to my questions in my initial post. Speedo (drive circuitry that's part of the unit) ? ECM? Speed Sensor?

Hoping someone else has experienced this.
Need more opinions please....

 

Bad speed sensor. But also what size wheels are you running on your car?

 

Its a 95 RS. Stock steel wheels with 205/70R14 tires. 1 size over the stock 195/70R14. That might account for 2-3mph difference at most. Speedo has always been wihtin a couple miles to near dead on passing radar signs until 2mos ago.

 

Thespeedo sensor is located directly on the transmission. I dont remember exactly how it functions however

 

I asked cuz the first set of low profile tires I ever got on the same size rims as the stock made my speedo read 7-8 mph faster than what I was doing.

 

I was leaning towards the sensor as the culprit but unsure since theres also circuitry to drive the speedo and I'm not sure if the signal comes directly from the sensor or takes a detour thru the ECM.

I was lookin for the sensorbut couldn't find it. Kinda crowded in there. Might be worth a couple bux to grab one off of a wrecked Mitsu or Dodge/Chrysler with a 2.0 / auto in the boneyard for a few bux IF I can find where it is. I'm sure the dealer gets a mint...and I'm not even sure that wud do it so I dont want to pay for a non returnable sensor at dealer prices.

 

Don't get really anything electronic from the graveyard..no tellin if it's good or bad and plus it could've sat there for a long time and moisture could get to it...just spend the extra money on a new one IF that is what the problem is but make sure that is your problem first obviously.

I remember monkeying with the speed sensor on my old '97 Spyder and I believe it's on the left side of the tranny as you are looking into the engine bay..I was able to reach in pretty easily to plug and unplug it..You may have to pry a "clip" off to remove it.