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2005 Trailblazer speedometer not functioning correctly
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mcgrant
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Jan 8, 2013, 7:24 AM
Post #1 of 17
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2005 Trailblazer speedometer not functioning correctly
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2005
Chevrolet
Trailblazer
4.2L I6
77,000 miles
I noticed following my wife one day that she was driving about ten over the limit. When we stopped I jumped her about it and she said the speedometer said she was doing 55mph. It started getting worse from there. It usually stays about ten to fifteen mph off, if it works at all. We were going down the freeway over the weekend and she used her GPS on her phone to check how far we were off and it said we were doing 70 and the speedometer was reading 55. I have a check engine light on, hooked up the scanner and got a P0128. My book says that is the coolant temp. sensor. I replaced the VSS and it is still not working right. I was on a Trailblazer forum last night and seen that there could possibly be two VSS on the vehicle. It said one was for the speedo and one helped with speed reading for shifting into four low. I wanted to ask a professional before I went any farther. I purchased the coolant temp sensor but haven't had enough time to get it on there yet.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 8, 2013, 7:50 AM
Post #2 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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I did find two sensors one for speedo and one for transmission speed. VSS was just $25 bucks and I'd probably toss it with that info and do kinda trust GPS speeds posted that match exactly for me so far.
The coolant or engine temp sensor could just be off a bit or it would be running lousy or perhaps a weak connection to it or VSS messed up that way too.
Unless you have tires on this thing so much bigger/taller than what it calls for which would give you the wrong speed and speedo works at all it about has to be sending the wrong signal. That or you don't want to know if the cluster is at fault.
Short of more intense code readings I think I'd toss the $25 bucks first and hate to waste a possible good item but today that's cheaper than getting a better diagnosis right now.
CTS can be checked with just a thermo and an ohm meter. So far few really have failed for real but easy enough on most also. If these issues are related you have to question wiring connections or you need better equipment,
T
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mcgrant
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Jan 8, 2013, 10:31 AM
Post #3 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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I was wondering if I replaced the wrong one. I will try replacing the other and see if that solves the issue. I will update later today or tomorrow. Thanks!
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mcgrant
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Jan 8, 2013, 11:05 AM
Post #5 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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Thanks, the stat looks a lot easier to change than the temp. sensor. Would that explain why it takes so long for the heat to start getting warm?
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Hammer Time
Ultimate Carjunky
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Jan 8, 2013, 12:48 PM
Post #6 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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It certainly would
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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mcgrant
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Jan 8, 2013, 4:07 PM
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Re: 2005 Trailblazer speedometer not functioning correctly
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I just got back out from under the car again. Replaced another VSS with the one I took out yesterday. I checked for bared wires near the connectors and found nothing wrong. I did notice there are three sensors within six inches of each other that all look like the VSS. Can you shed any light on how I can tell them all apart? I tried finding a schematic, but was unable to find anything on the net. I suppose the smart thing to do is take ohm readings on all three and see which one is the devil.
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Hammer Time
Ultimate Carjunky
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Jan 8, 2013, 4:36 PM
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Re: 2005 Trailblazer speedometer not functioning correctly
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Is it 2WD or 4WD?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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mcgrant
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Jan 8, 2013, 4:43 PM
Post #9 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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It's 4wd. I'm pretty sure one of them is for the 4wd. There are two on top of the transfer case close together, one on either side. The other is right above the motor thing (can't remember the name). I'm pretty sure that is the one for the 4wd and its also the one I swapped out yesterday.
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Hammer Time
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Jan 8, 2013, 4:45 PM
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Re: 2005 Trailblazer speedometer not functioning correctly
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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mcgrant
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Jan 8, 2013, 4:53 PM
Post #11 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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I replaced that one today. There is one directly to the left of that one also. I'll take a picture tomorrow and post it.
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Hammer Time
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Jan 8, 2013, 5:24 PM
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Re: 2005 Trailblazer speedometer not functioning correctly
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If your speedometer works but is inaccurate, it's likely due to a sensor. Have the tire size or differential gears been changed?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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mcgrant
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Jan 8, 2013, 5:46 PM
Post #13 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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As far as I know it's all stock. We bought it used about six months ago, I do know the tires are original size though. I'll know tomorrow if I changed the right sensor after my wife drives it
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Hammer Time
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Jan 8, 2013, 5:50 PM
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No, you won't because the sensor isn't likely the problem.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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mcgrant
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Jan 8, 2013, 5:55 PM
Post #15 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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So am I looking at a computer, cluster or wiring issues?
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Hammer Time
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Jan 8, 2013, 5:56 PM
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Re: 2005 Trailblazer speedometer not functioning correctly
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Or the wrong speedo gear in the transmission or PCM programming.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Jan 8, 2013, 5:57 PM)
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mcgrant
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Jan 8, 2013, 6:03 PM
Post #17 of 17
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Re: 2005 Trailblazer speedometer not functioning correctly
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Okay, thanks. I will have to take it to a garage for that one. I don't have the tools for the PCM and really don't want to dig into the tranny. Never tried it before and really shouldn't practice on the wife's car.
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