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Davo
Davo, Master technician
Category: Car
Satisfied Customers: 3253
Experience:  ASE Master Technician/Advanced Automotive Diagnostic Technician
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2000 chevrolet: 5.3L Z71 speedometer..new insrument cluster panel

Customer Question

2000 chevrolet 1500 5.3L Z71 speedometer does not work. A new computer has been installed , a new insrument cluster panel has been installed, and it has been flished. The tech seems to think it is a Class II Serial Data Communications Failure, but does not know what that means.
What does it mean, and how do I fix the speedometer.
the check engine light is on also.
Submitted: 12 years ago.
Category: Car
Expert:  Joe Barcus replied 12 years ago.
did your tech check to see if voltage is at the odo fuse? did he look at the box on the transmission? your check engine light will remain on until its cleared up
Expert:  Marc replied 12 years ago.


Did the tech read the codes and what are they, (the code numbers)
Expert:  Davo replied 12 years ago.
Yes I would like to see code numbers also.
Customer: replied 12 years ago.
Reply to Marc's Post: The code is 608 Output speed sensor circuit fault. A new speed sensor was installed and still didn't work.
Customer: replied 12 years ago.
Reply to Davo/diablo666's Post: code 608 output speed sensor circuit fault. put a new speed control sensor and it still does not work
Customer: replied 12 years ago.
Reply to Joe Barcus's Post: yes voltage checked O.K. code is 608 output speed sensor circuit fault. put a new speed control sensor on and it still doesn't work.
Expert:  Joe Barcus replied 12 years ago.
these kind of problems are hard ones to pin down, if you know for sure the + voltage is there than it must be in the ground. maybe the plug is bad on the sensor??? Im not sure of the voltage that needs to be at that plug one of the other guys should know this in a while.
Customer: replied 12 years ago.
Reply to Joe Barcus's Post: when the new speed sensor was installed the code was cleared and put into gear and the code immediately returned. tried this several times but it still came back and the speedometer still doesn't work.
Expert:  Joe Barcus replied 12 years ago.
I might very well be fishing here and Im sure I am. so If I look like to big of a fool forgive me.
sounds like something in the wiring harness going down to the transmission, un hook batt once more let it clear, and start it again. by what you said it wont show code until you use the shifter. if thats the same way every time then its "could be" two wires touching in the harness going down to the trans. taking the ground away. again this is just guess work.
Expert:  Davo replied 12 years ago.
P0608 is not an output speed sensor code.It is a vehicle speed output circuit code which is a different animal.This code is triggered because an output of the pcm sees a fault not an input as in a speed sensor code would be.There is a dark/green white wire that goes between the pcm and the ipc.It goes to the fuse box along the way and there is at least 1 other dark/green white wire in there.I suggest you get your mechanic to see if the dark/green white wire is open.Just so he doesn't get all confused it is not a class 2 failure those are communication failures and are listed as U1000 series codes.But then maybe his scan tool won't read U codes I don't know.If he has a wiring diagram he can find the wire I would hope.There is also a connector between the pcm and the ipc shown on the wiring diagram.The pin number at the pcm varies according to engine size but the cluster pin number should be A3.Let me know where this gets you.Is your mechanic capable of doing electrical circuit checks?
Customer: replied 12 years ago.
Reply to Davo/diablo666's Post: Checked the dark/green white wire for resistance, checked O.K. Checked on both sides of the plug in between the IPC and the PCM everything checks O.K.
When you unplug the IPC and plug it back in all the gauges come on including the speedometer. Unplugged the speed sensor on the trans and truck would not shift. Plugged it back in and it shifted fine.
Went throught the checks and still cannot find anything.
Also have now noticed that the towhaul button on the shifter works intermittenly, don't know if this has anything to do with it or not.
Expert:  Davo replied 12 years ago.
If it were me I would disconnect the dark green/white wire and run a new temporary one to see if it works after that.Your wire could show continuity and still be shorted to ground or not be able to carry any current.I'm curious as to what your resistance reading was so please post that.
Customer: replied 12 years ago.
Reply to Davo/diablo666's Post: I don't remember exactly what the resistance was, there were 2 dark green/white wires in question. when you put it on one it would jump around, when you put it on the other it would settle out. The wire was showing almost 11 volts with the key on.
Expert:  Davo replied 12 years ago.
You can't do a resistance check on a live circuit/wire the results would be incorrect at best.I could tell you how to voltage drop test the circuit in question but feel if you run a new wire the results will be more conclusive and lead to a faster repair.Did you test the wire for a short to ground or voltage?If you didn't replacing that wire is the easiest step to take.