I was driving down the interstate with cruise set at 75 an my truck jerked twice an my cruise cut off. I tried to rest it but it wouldn't. Then I noticed my speedometer wasn't working. Truck will still crank an drive but acts like it has no power an will only at up to 16 psi of boost.
Any ideas what could have happened to it to make it do this will be a big help.

 

Bump. Bump.

 

Might be the speed sensor in your rear differential. Check the wiring to it. Is your ABS light on?

 

ABS light has been on for a year or so. The wire to the left front ABS sensor got pulled apart. I wasn't sure it speedometer worked from sensor or a gear like in old style transmission.

 

Not three hours after I bought mine I was driving home from Houston with the cruise on and it bucked twice and kicked the cruise out. The ABS light came on at that time. If memory serves, I think I may have lost speed as well, or it was reading well below actual speed.


I have intermittent speedometer issues when it is below 50 F outside. Often it will read during the first mile or two, and either trend to zero or I'll notice it at zero. No rhyme or reason though, and it is ambient temperature dependent. I had my VSS sensor out and it looked ok, but haven't replaced it yet.


I never have had the ABS light come on again, although I'm not sure I've ever used cruise since that time.


This is purely a guess, but I wonder if the cruise using the ABS sensors to operate, and any malfunction will kick the cruise out?

 

What sensor doin the computer get its signal for ur speed.
My scan gauge isn't showing any mph while in driving

 

I think the speedometer gets its signal from the VSS in the differential, but I wouldn't swear to it.

Ive never lost speed readout on the SGII when my speedometer falls out.

Makes me wonder if I've got a cluster issue and you may have a VSS issue? We need some help determining what signals go where.

 

The speed signal comes from the differential sensor, goes to the ABS controller where it's calculated and then distributed to all the systems of the vehicle, PCM, speedometer, and anything else.

Some later model ABS controllers upon failure of the reading from the differential sensor will use one of the front sensors as a replacement, but typically the yellow ABS warning light will stay on warning that the ABS operation is compromised.

There also can be situations where the speed signal is erratic and the ABS computation can't be made competently, so the speed signal will not be transmitted to other components, but the ABS warning stays off. It's unusual, but it has happened.

The ABS differential sensor has the highest failure rate between all the wheel sensors, hampered my the metal contamination of the diff entail lubricant. If they are coated with metal debris, sometimes they still work if the debris is removed, but that level of contaminate is a good indication to change the differential lube. But sometimes it just fails and needs to be replace.

High mileage vehicles also have a history of a break in the wiring to that sensor due to constant flexing.

 

My scan gauge shows no codes so I guess I will pull out speed sensor in differential an look at it. Clean it off an see if that helps my no speedometer problem

 

Jack,


Thanks for the information, that is extremely helpful.


I have had one case where my cruise kicked off and my ABS light came on. Ambient temperature probably 40 F. I did not have an SGII at this time so I don't know to what extent I lost the speed signal.


I have had several instances (pretty regularly) where my speedo will stop working for some period of time. These always occur under 50 F. No codes or ABS lights are present. I have always been able to read speed on my SGII.


Based on what you wrote above, it seems most likely that my VSS is working, as the computer hasn't failed to report vehicle speed during my events. If I was to guess, the VSS signal is either becoming corrupted on its way to the cluster or by the cluster itself. Some light reading indicates that the '06s have a track record of cluster problems, although my intermittent speedo is the only issue I have to date.


Any idea if the ABS unit, when the VSS signal is not present, would use a wheel sensor to send a signal to the cluster? If it does, I believe this would just about eliminate the VSS and let me focus on the cluster. If it doesn't, I suppose I could still have a VSS issue, although it seems unlikely with what I now know.


Thanks again.

 

If your speedo stops then try the cruise control. If no cruise then start at the rear axle speed sensor since that is the input for both. If cruise works I'd start at the cluster.

Also Forscan app with a bluetooth OBDII elm327 adapter reads all speed sensor inputs at the PCM and ABS modules. Great for diagnostics. Look under ABS module for individual wheel sensors. Under PCM module you can see tailshaft speed, vehicle speed, & vehicle speed faults.

 

Pete has it covered better then I did.

 

Thx for all the help. I been working out of town an haven't been able to work in my truck. I did notice that my fuel gauge is acting crazy. It won't show drop in fuel level until u switch trk off an then restart it.
Any ideas on that ???

 

Well. Oil cooler when out on me an I had to replace it. It started mixing oil in the water but no water in the oil. Once I got that fixer I spliced both my ABS sensor wires back together an my speedometer started working again an my fuel gauge works properly now also.
I guess if PCM doesn't get any readings from both ABS sensor then ur speedometer will not work ur fuel gauge will act crazy an ur trk will not have its normal power.