JWylde101

Hi Everyone, so my 1991 Chevy Corvette is acting up bigtime. The problems started about 2 weeks ago. I took her in for a simple oil change and fluid topping off. I took a short camping trip and when I got back, she started running rough. I noticed that all of a sudden, the digital speedometer was not responding normally and was fluctuating from 28mph then to 12mph, then would drop down to 10mph and then 0mph even while I'm driving. Now the speedometer does the same thing but mostly stays at zero. Next, while I was driving on the city streets, my "Service Engine Soon" indicator turned on for a few seconds and then shut off. Next time I went out I was on the freeway and the same indicator came on, along with the battery indicator only this time the car was acting like it was gonna shut off and I felt my wheel start to lock up until just then I was able to pull over and she had already shut off. I reluctantly turned her back on and she started just fine, it was just that the speedometer didn't work. I'm beginning to notice the "Service Engine Soon" indicator only comes on if I'm going at relatively high speed. Also, if I hit around 55mph or so, she needs to be shifted into Overdrive, but I do not hear her shifting the way she always has. It sounds like she's almost stuck in Drive. I don't get any other warning messages, it's just that she's riding really rough. I saw some people talking about it being an issue with the VSS but if anyone has any other suggestions, I would definitely appreciate it. I need to take her in for servicing but I want to be as knowledgeable as possible before the mechanics try to take advantage. Thanks for your help guys!

Jenn

Cliff Harris

The VSS (Vehicle Speed Sensor) in the transmission sends a signal with a frequency proportional to vehicle speed to the dash. It sounds like you have an intermittent connection in that wiring.

The usual test is to pull out the VSS and turn it with an electric drill. The dash should register some speed in MPH that is proportional to the speed of the drill.

JWylde101

Thanks Cliff!

WVZR-1

Do you intend to do the diagnostics yourself OR a "FOR HIRE" service?

I don't think you remove the current VSS for a start.

You/shop either check and confirm the connector to the VSS and then maybe:

You might buy an appropriate VSS locally and connecting it to the connector on car and confirming the speedometer operation as Cliff suggested. The SES is on because of the intermittent VSS. Ask the auto parts store that if the VSS isn't installed is it returnable. If it's an in stock or standard part I'd think return isn't an issue. There's several VSS that could be used for the diagnostics. I might not mention the diagnostics intended!

If it's a "FOR HIRE" I believe you discuss it first.


Is the shop that did the service the same shop that would be doing the diagnostics? Do you have a relationship with them?

****** INTERMITTENT and FLUCTUATING might be of interest here, perhaps the retaining clip has failed on the drive gear on the 4L60 output. If you found the connector to be good and the speedometer registered with the VSS then you need to consider some options. I think that the intermittent/fluctuating needs to be considered for your particular case.

This isn't an A4 with a VSS but the drive gear is the same. If the clip fails I believe you get the intermittent/fluctuating. It can be visually diagnosed by removing the VSS and rotating the drive-shaft.

JWylde101

Thank you WZR-1! Well I have a coworker who's boyfriend has a mechanic shop so I can take it to him to get checked out and I trust them. We'll see how it goes. I just really want her back to normal again so I can tear up those streets!