Cluster stepper motors and odometer problems.

[dcbenvoy]

Hi,

I am a transplant from the other site.

My gas gauge went first so I assumes it was the sensor in the tank; and it may be.

Then my speedometer started fluttering too. so I bought stepper motors and i'll replace them next week.

Now I have noticed that anytime my speedo stops working my trip gauges and odometer stop counting! Not one has notices this problem. Most have said the used their trip meters to gauge their fuel but I can't because everything is unreliable.

My question is this. Do the trip meters and odometers work as a result of the needles moving? Or do I have more problems than just stepper motors?

Thanks, Doug

 

[The_Roadie]

Welcome!

The gauge needles are nothing more than displays. The memory is elsewhere, and the data should be kept even if there's no gauge cluster in the vehicle. Otherwise unscrupulous owners would just pull the fuse for their instrument panel to keep from racking up miles and going out of warranty.

The main sensor used for speed and mileage is near the main driveshaft (transmission tailpiece for 2WD, transfer case for 4WD) and is called the VSS. The vehicle is programmed at the factory with the tire size and the gear ratio, so it knows how many pulses of the VSS equal a mile.

If you lose your speedo, and the trip odometer stops updating, does it catch up when the speedometer recovers? For instance, if you drive two minutes with the speedo off, and then it comes back, does the trip odometer jump up the proper amount of distance, or does it permanently "lose" that distance? In the first case, you might have a data transmission error from the PCM to the gauge cluster. But if that happens, other things should quit working. If it's the second case, then your VSS sensor or circuit might have a problem.

The way to troubleshoot it is to get a Scangauge or a scan tool that can look at the data that's available from the PCM, and see if the PCM thinks you're not moving when the speedo is displaying bad data. I would have thought if the VSS is flaky, that you'd also get very poor shift performance out of the transmission, and probably a SES code.

 

[dcbenvoy]

Roadie,

Thanks for the response. Interesting.

The trip and odometer gauges do not catch up. But I have no ses and it shifts fine.

also the range info is blank when the gas gauge is not on "E" but it is totally wrong whenever the gauge goes above "E"

 

[The_Roadie]

I think you have to get a good scan tool and drive around with it looking at the data stream when the problem happens.

 

[dcbenvoy]

I forgot to ask. It is a given that I should still proceed with the stepper motor intsall?

I may need a real tech to handle the scan and repair. No?

 

[The_Roadie]

I'd defer the stepper install because you might not need it. If you located a buddy with a good scan tool, you wouldn't have to pay a mechanic. Or wanted to invest in one. Might be $200, but then you have it forever.

 

[dcbenvoy]

How complicated would the repair or repairs be. The scan purchase might be pointless is I can't fix the problem.

which scan tools would you reccomend? I don't suppose the one that works with the iphone would be any good?

 

[The_Roadie]

Could be wiring. Could be a flaky VSS. Impossible at this point to say since the root cause isn't known. I have an android phone and our available app is different from the iphone one. See if the iphone app can display VSS data.

 

[dcbenvoy]

Roadie,

I can't thank you enough for the time you spend on these forums helping people. Lately I have questioned my loyalty to this vehicle but truth be told I really love it.

I am inspired that it looks like you bought one too. I seem to remember you had a trailblazer.

I will follow your advice and check back when I know something.

Thanks again, Doug

 

[The_Roadie]

Bought a trailblazer? Pooh.

View attachment 18224

 

[dcbenvoy]

I know you have an envoy now. I thought you used to have a trailbazer. My bad.

 

[dcbenvoy]

I see why. I saw the offroad TB thing and assumed you had a TB.

I just checked out your build thread. WOW. You da man.

 

[The_Roadie]

...offroad TB thing ....

Yah, I'm a founder of that site and didn't insist on a more inclusive domain name when we started it up. My bad.

 

[dcbenvoy]

Roadie,

Which side driver's or passenger of the transmission tailpeice is the vss located. I want to visually inspect that thing and it's wiring.

Also when you replace a bad one will the lost miles update themselves or are they just gone?

One last question, sorry. When getting a scanner and being sure it reads vss info; does that just mean it reads the speed the car is going? alot of them say they read vehicle speed and not the vehicle speed sensor. Or same same?

Thanks again, Doug

 

[The_Roadie]

There is only one VSS that tells the PCM how fast you're going. It's what the scan tools all read. If the sensor or wiring is bad, the miles were never recorded in the first place. Like disconnecting the speedometer/odometer cable back in the days of mechanical gauges.

There are two identical sensors on a 4WD vehicle's transfer case. I've looked for years for exactly which one is for the VSS and which one goes to the TCCM to control the A4WD activation. Haven't found that clue yet in the shop manuals. Just look at both. Oooops, just thought of a way to check. The TCCM is fed by a sensor whose wiring colors are light blue and dark green. The vehicle's VSS is wired with light green/black stripe and purple/white stripe. If you look, perhaps you can tell us? Items 2 and 3 in the second drawing

View attachment 18255

View attachment 18256

 

[dcbenvoy]

Ok I found it. great information thanks. It is on the driver's side.

Here is a picture. Loks like a green wire and a purple wire.

 

[91RS]

The memory is elsewhere, and the data should be kept even if there's no gauge cluster in the vehicle.

It isn't stored elsewhere. I'm not going to elaborate, but I think you will know what I mean.

 

[dcbenvoy]

If I take my cluster out today. Can I drive with out it? In case I have to run out for something.

 

[The_Roadie]

You can drive without a cluster just fine.

 

[dcbenvoy]

I replaced the stepper motors. they all did what they were supposed to; that is when I plugged the cluster in the needles jumped and returned to their 0's.

except for the gas gauge, instead of going from "E" towards "F" it went backwards and pointed down.

now I don't know what to do.

 

[The_Roadie]

Just put the needle on in a different orientation. Lather, rinse, repeat.

 

[dcbenvoy]

After messing with it it different positions the light came on ant it went to empty. The tank is completely full. I am left to assume that the sensor is bad. I had already ordered the motors before we started discussing the problems on this thread so I if my steppers arent bad they will be sooner or later so I went ahead and replaced them.

My next step will be to get the OBD2 scanner and let it tell me what the heck is going on.

Sound reasonable? (ofcourse it does; that's what you told me to do in the first place.)

 

[AtlWrk]

Another possibility for your speedometer issue:

TSB 07-08-49-027