Bouncing Speedometer

**ottoman** · 10-25-2010, 09:26 AM

Hi,
Lately my speedometer has been bouncing up and down. It's intermittent. Usually it works fine but then it will start to bounce down and go up again. Looks like it's a loose wire but before I spend a lot of time looking around for it I thought I would ask if someone here is familiar with the problem.
It seemed to have begun days after I replaced my starter so I'm not sure if it's related.
2001 SS Camaro.

**bberretta** · 10-25-2010, 12:20 PM

Had a similar problem on a prior car and it ended up being a speed sensor going bad. Maybe you accidently knocked it loose? It's mounted on the transmission.

**ottoman** · 10-25-2010, 04:20 PM

Hey thanks Berretta,
Exactly, I was wondering if it got knocked loose while working on it.
Did yours throw up any trouble codes when it went bad? Do you know any way to test it?
I'm going to try pushing the plug firmly on and maybe wiggle the wires to see if it helps.

**bberretta** · 10-25-2010, 05:05 PM

I don't remember any codes, but its been quite a while. The way I knew it was bad was because the plastic was cracked- a little obvious! There are two different sensors- one for a manual and one for an auto but neither are more than $35- keep in mind this is not the same as the ABS/TCS speed sensors which cost $50-$110 each!

**ottoman** · 11-02-2010, 03:58 PM

Turned out to be a bad ECM. Maybe it got fried while trying to boost my dead battery.

**redss70396** · 11-05-2010, 04:47 PM

How did you determine it was the ECM ? I am also having the same problem with 2002 SS after trans install.I replaced the sensor but still doing it - and car is really acting crazy. I suspect the ECM but don't want to throw money away

**redss70396** · 11-07-2010, 04:16 PM

Speedometer is getting worse after sensor was replaced.

**ottoman** · 11-08-2010, 10:16 AM

Hi Red,
I was really busy at work the past few weeks and I didn't have any spare time to figure it out so I took it to a mechanic. He spent a lot of time and ended up ordering and swapping in a computer. It runs fine now.

My symptoms were that the speedometer would drop out and come back after a second or less. No other effect on the engine. My commute is 1/2 hour and it started happening 3-4 times during each trip. Over the course of a week it got progressively worse. Maybe as much as 25 times a trip. I then started to feel a slight miss when it dropped out and was planning on taking it to a mechanic when the car completely died. I ended up towing it to my mechanic after that.

While searching around for possible causes, I found a guy on ebay called "spareecm" that would sell a used ECM programmed with your VIN (you provide) for $90 plus shipping. He said that there is a procedure to re calibrate the crank trigger/reluctor wheel after you've installed the unit.
For $90, I was considering getting one as a spare in case this happens again.

Hope this helps,

**redss70396** · 11-08-2010, 06:01 PM

I am thinking this is my problem too as now engine is cutting out or temporarly dying out under full throttle. I am taking to tuner for them to figure out. Thanks for yor help.

**ottoman** · 12-27-2010, 12:53 PM

Hi Red,
Any update on what your problem was?
My speedometer just started bouncing again this morning. It's not missing or anything, it just started bouncing for 5 seconds or so at 65mph and stopped.
Everything worked fine for over a month since replacing the ECM. Now I'm worried that it's starting all over again.
We've been getting a lot of rain lately. I'm wondering if it's related.

**redss70396** · 12-27-2010, 03:27 PM

I can't say for sure what caused the bouncing. I took the main harness loose at the trans and covered it with dilectric grease and plugged back in. Also found the battery ground at battery was a little loose. All I can tell you it all started working correctly after that and hasn't missed a beat since. Maybe you can try the same. I also re-did the shift kit in the trans at the same time but I am almost 100% sure that wasn't the fix for stalling engine or speedo problem.Had to be the main harness or ground @ battery.I do know that the small harness to speed sensor wasn't the problem. Hope this helps.

**ottoman** · 01-03-2011, 09:26 AM

Hi Red,

Following your idea of cleaning up grounds, I cleaned up four body ground connections under the hood (Left/right fenders, left/right rad support). I also found a loose ground connection on the back of the drivers side cylinder head. It was really loose and really hard to get to. The previous owner had a mechanic dismantle the top end looking for the source of a ticking lifter. It turned out to be a lifter tray that wouldn't have caused a problem anyway. My guess is that the mechanic didn't tighten the ground sufficiently. It's really hard to get a wrench in it. I had to remove an aftermarket strut tower brace and a spark plug wire to get a stubby wrench on that bolt. I could only turn it 1/8 of a turn with the tips of my fingers.

So far, over a few days and about 60 miles, I haven't seen the problem re-appear.

thanks for your suggestions.

BTW, I found the locations of the grounds by following the schematic at:
http://www.tafmotorsports.com/images/wirecodes.pdf
and
http://www.tafmotorsports.com/images...g.diagrams.pdf