I posted this on clubgp but no one really answered and it really doesn't have anything to do with tuning but I was wondering if any of you had any ideas. What is happening is when I'm cruising down the highway at like 65, all of the sudden the speedometer drops down to like 8-10-20 mph, then pops back up to 65 or whatever I'm cruising. Sometimes it does this for several seconds. Any ideas what could be causing this? Where does the speedometer get its reading from?
2005 Grand Prix GTP
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what is make model? without knowing your car how we can help you?
It's a 2005 Grand Prix and it is in my sig, lol.
2005 Grand Prix GTP
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I have excatly the same car, never experienced that on mine.
But I remember seeing that on rental cars like Chrysler 300 C or Buick LeSabre...
If you don't see the drop in your HUD or Scanner, then it could come from a connection in the harness of the speedometer.
Oh no it drops on the hud too. The hud and the speedo. I guess I should just scan it and see if there are any codes. The idiot light is not on.
2005 Grand Prix GTP
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Typically the speed sensor is in the transmission. On my 2002 L67 (and probably yours too) it's way on the passenger side, and it hangs out the top of the transmission.
The speed signal goes from that sensor to the PCM. Then, the HUD and cluster speedo get their signal from the PCM. Make sure your scanner shows the drop, and make sure the connector and wiring is tight and in good condition before replacing the sensor. With a jack, some jack stands and a small socket set it's not too hard to replace.
Thanks, I had a feeling it was something with the tranny.
2005 Grand Prix GTP
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Originally Posted by Perforator
This happens on my 03 Trailblazer also. Intermittently.
Mitchell
'04 Supercharged MC SS
MOD LIST
Custom PCM, Ram Air Hood w/ Air box, Intense MPS w/3.6", R/T DP with Ubend delete & HF CAT, LC-1 WB, GMPP Cat Back, Jacobs wires, 180 T-stat, & an Optima Red Top
Is there a VSS buffer on these cars? This sounds like the old digital dashes on the Grand National having an intermittantly bad VSS buffer.
Central TEXAS Sleeper
Experimental Physicist
Current:
1964 Riviera (4.1L Buick Turbo6, 4L80E, L67 PCM)
2012 Hyundai Genesis Sedan (3.8 GDI, 8spd Aisin)
1998 Chevrolet Suburban K2500 (454, 4L80E)
SOLD:
1970 Riviera
1965 Riviera GS (465 Super Wildcat, SP400) #'s Matching
1967 Skylark Deluxe
1997.5 Regal GS
Nope, on his the VSS (Vehicle Speed Sensor) signal goes to the PCM, then the IPC (Instrument Panel Cluster) gets the VSS via Class 2 serial data from the PCM.
Perf - are you seeing this in your scan? The HUD is coltroled by the IPC, so if there is a problem in the IPC then it would be reflected in the HUD.
-Eddie
1998 GTP - 3.4 [3.2] [3.0] MPS - custom CAI - F.1 Ram Air hood - XP Cam - Ported Heads - 1.84/1.60 Si valves - 1.6 HS Roller Rockers - 72mm Ported TB - LQ4 MAF - 42.5# Lucas Injectors - Pacesetters
1/4 PB - 13.025 @ 106.81 MPH w/ 2.069 60'
2021 Chevrolet Colorado 2.8 Baby Duramax
I haven't had a chance to scan yet. It's happening on the speedometer and the hud. This morning it was really bad. Doing about 40 and the speed read 0. The tranny is acting kinda wierd too but it's probably because of the speed jumping all over the place. Anybody know the part number for the VSS? I emailed gmpartsdirect and pace parts and nobody replied yet.
2005 Grand Prix GTP
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Should be a 213-3241 Declo #
-Eddie
1998 GTP - 3.4 [3.2] [3.0] MPS - custom CAI - F.1 Ram Air hood - XP Cam - Ported Heads - 1.84/1.60 Si valves - 1.6 HS Roller Rockers - 72mm Ported TB - LQ4 MAF - 42.5# Lucas Injectors - Pacesetters
1/4 PB - 13.025 @ 106.81 MPH w/ 2.069 60'
2021 Chevrolet Colorado 2.8 Baby Duramax
So if I scan, besides looking for codes I should be watching the scanned vehicle speed. If the scanned vehicle speed drops like the speedometer then it's probably something with the vss/cabling, if the scanned vehicle speed does not drop it's probably something with the instrument panel, is that correct Eddie?
2005 Grand Prix GTP
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Exactly!
-Eddie
1998 GTP - 3.4 [3.2] [3.0] MPS - custom CAI - F.1 Ram Air hood - XP Cam - Ported Heads - 1.84/1.60 Si valves - 1.6 HS Roller Rockers - 72mm Ported TB - LQ4 MAF - 42.5# Lucas Injectors - Pacesetters
1/4 PB - 13.025 @ 106.81 MPH w/ 2.069 60'
2021 Chevrolet Colorado 2.8 Baby Duramax
Ok I'm definitely going to scan tonight when I get home.
2005 Grand Prix GTP
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Murphy's law. This morning when it started it happened less than 5 minutes after I left my house. Tonight I went for a 30 minute drive and it didn't happen at all,lol. No tranny codes either.
2005 Grand Prix GTP
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Hold the presses. Just checked the scan. There is one frame where it dropped from 58 to 46 and then back to 54. Didn't even notice it on the HUD and it only happened once in the whole scan. I guess I'm going to check the wiring/plug when it cools down.
2005 Grand Prix GTP
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The car had been fine all week. Then yesterday on the way to a pool party with my son all of the sudden the speedo read 0 mph even though I was cruising down the highway. It stayed like that all the way there (about 10 minutes of driving) and when I stopped I checked the codes and it threw P0503 which is VSS signal low input or something. Luckily when I left it started working again. I ordered another VSS sensor when I got home.
2005 Grand Prix GTP
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Sounds like a good call - good luck!!!
-Eddie
1998 GTP - 3.4 [3.2] [3.0] MPS - custom CAI - F.1 Ram Air hood - XP Cam - Ported Heads - 1.84/1.60 Si valves - 1.6 HS Roller Rockers - 72mm Ported TB - LQ4 MAF - 42.5# Lucas Injectors - Pacesetters
1/4 PB - 13.025 @ 106.81 MPH w/ 2.069 60'
2021 Chevrolet Colorado 2.8 Baby Duramax
I had VERY similar issues with my 2004 GTP. After chasing my tail for a few weeks, scanning and troubleshooting...
In my case it ended up being the connector on the back of the IPC.
The connector was like kinda worn out and would make contact and then not and so on..
HTH
Shane
Engine
2004 GTP, 1.9 Rockers, 3" Catless DP, 3.5 MPS, 180* t-stat, AL104's, FWI, HPT (pro) . LS1M scanner.
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