When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a 1999 C5 Corvette. Bit of a storied history here with issues recently. However, I've managed to get them all fixed. Down to two issues with the cluster.
Left turn indicator stuck on Issue one when headlamps are up, the cluster illuminates (but does not blink) left turn indicator. It's stuck on. If I select a left hand turn it'll behave normally till I put turn stock back to normal position.
Speedometer doesn't register speed this is the more elusive. I pulled the cluster and validated harness is good as well as PCM. I even put an oscilloscope on my dash and drove to see the VSS Signal was being generated at the connector for the cluster. It is. The speedometer passes the self test / sweep at start-up too. However, it doesn't register speed at all.
Bench testing: currently I have A13 & A14 to Power w/ B13 & B15 to ground. I'm pumping in 50hz 10vpp to A7 VSS Signal. The cluster does power up, draws about 0.6A @ 12V. It sweeps the gauges and illuminates various trouble lights. However, I cannot get the speedometer gauge to register speed at all.
I pulled the cluster apart. I can find no burnt parts on the circuit board or bad components on visual inspection. I powered everything up and supplied VSS signal. Then applied pressure to random spots across circuit board to see if maybe I have a bad connection / solder joint somewhere. No luck.
Last edited by weinerschizel; Jun 24, 2023 at 08:20 PM.
Note that this is a new thread on the same problem because his original got bogged down in electronic PCM and sensor testing, signal generators, oscilloscopes and such..
We concluded that the PCM is outputting a proper speedometer signal, but it never gets to the speedometer. He is very electrically knowledgeable and as far as I can tell everything obvious has been tried and checked.
His original post is: https://ls1tech.com/forums/pcm-diagn...g-pcm-vss.html
I called a speedometer shop in Tucson, Arizona. The guy was SUPER knowledgeable and gave me LOTS of tips. First most obvious was...
See if odometer turns. He said the odometer in the dash runs off the VSS Signal as well. I know my 2001 Tahoe updates the odometer off the VSS signal as well. However, Corvette seems to be a slightly newer design despite being two years older.
I think a couple years later GM changed this up & BCM stores odometer reading along with VIN in BCM & CLUSTER item so a Tech 2 Programmer is required for newer stuff...?
I'll put the cluster back in the vehicle and drive a mile or so to see if the odometer updates.
Either way, I'm getting VSS Signal to the cluster and the pinout has a good connection to the circuit board... I was able to trace it a few connections in but must be more than a two layer board as I loose it from there and don't have a schematic. Circuit board looks immaculate. Honestly, it's abundantly clear the folks on the Corvette team take pride in ownership. The quality of this piece and the dash is FAR superior to any other vehicle I've worked on before. Despite owning this car for 17 years, I've never had to work on it until now.
Odometer does not update / respond. I tried the trip meter as well. Neither are responding. This is VSS Signal output HERE
Sorry for poor quality, I didn't know how to record the waveform on my oscope. It's roughly 12vpp. However, I notice it's centered on Zero volts, instead of the lowest point being zero volts. Essentially it's going from -6v to +6v. Anybody know what the VSS Signal waveform should look like? Is mine correct? I also noticed my bench test of the PCM VSS Signal went from 0V to Battery Voltage, not -6v to 6v.
Not sure if this is related. However, when the speedometer started to flake out, the dash illumination would flicker unless I turned on the headlights. Around that same time the speedometer started to stop functioning. It would work intermittently, now not at all. I notice the left turn indicator sticks (only on the cluster not on the turn lamp) once headlights are turned on. Related issue?
For my records the dash is at 101850
UPDATE: I'm assuming the VSS signal needs to be 0V to 12V or thereabouts. Reading HERE
Last edited by weinerschizel; Jul 13, 2023 at 06:29 PM.
Anybody know, if I loose a ground can the VSS Sensor input to PCM mess up the VSS output? The wiring diagram eludes to this NOT being the case but that doesn't capture how the signals are process internally to the PCM.
Reason I ask is the driver rear chassis ground behind tire on frame is loose. I need to figure out how to fix that. It was a self tapping sheet metal screw in there. When I went to clean the ground and put it back in, it very easily stripped the hole.
I put cluster back in and ran HP Tuners to double check and PCM does know correct vehicle speed.
Cruise Control is non functional. It gets the signal from the multifunction switch but cannot set a speed as I assume there's no VSS Signal to it either.
My next plan of action is to pull the PCM and the cluster. Bench test them both at same time to see if I can get direct output form PCM to command speedometer on cluster... That be the case there must be a fault / short in the harness somewhere creating a fault in the VSS signal.
Cannot figure out why my Throttle Position Sensor is reading 0 Volts, despite it's a throttle by wire, I read factory service manual and still has a TPS sensor. Pulled codes and don't have anything DTCs for throttle position. I'm going down this rabbit hole because the Throttle Actuator Control (TAC) takes user inputs from the multifunction switch for cruise control. These are then passed onto the PCM for desired cruise control setting and the PCM commands the TAC accordingly to maintain the set speed.
I pulled my PCM and the cluster. Went to test the two together. Cannot get the PCM to output VSS Signal as before. I think there maybe something wrong with my PCM. Confused why it worked before and not now. I have even recorded a video of VSS Signal output working at my desk.
I did noticed there was a typo in my old PCM bench test thread correct in below as that thread has been locked out.
Blue: Pin 1 & 40 Red Pins 1 & 40 to ground Blue Pin 19, 20, & 57 to Power / 12 volt
Red Pin 20 to VSS low & Pin 21 to VSS high from function generator Red Pin 50 VSS signal output.
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Slideshow: From wobbling harmonic balancers to failed EBCMs, these are the issues that define long-term C5 ownership and what repairs typically involve.
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Slideshow: A modern Camaro transformed into a retro icon, this limited-run "Bandit" build blends nostalgia with brute force in a way few revivals manage.
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Slideshow: Cadillac didn't just crash the high-performance luxury vehicle party, it showed up loud, supercharged, and occasionally a little unhinged...
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Slideshow: A one-off sports car that looks like a vintage Italian exotic-but hides a C6 Corvette underneath-just sold for the price of a new mid-engine Corvette.
BENCH TEST? Speed not registering on C5 cluster 
