Speedometer/transmission problems

Asked by May 01, 2015 at 10:08 PM about the 1994 GMC Sierra C/K 1500

Question type: Maintenance & Repair

Ok my speedo is at zero and
occasionally twitches but it acts like
it is just in first gear what could
cause it. Now keep in mind that I
have already changed 2 different
ecm's,3 different speed sensors and
the speed stepper 2..... As well as
checked all of the wiring and
changed the transmission please
please please help my fix my
truck...... All of u guys know the bond
between a man and his truck lol

38 Answers

I'm at the point of scrapping it so please please please help


Read the service codes,google the codes find your pinpoint tests, run the tests. A trans that wont upshift at all can have numerous possible causes, a speedometer inop that blips can have numerous causes. incliding the gaugepod itself. the system can have a translating component, at least they used to. so when you were inspecting the wiring behind the gauges, did you encounter a governor or translating component ? Did your tests include checks to and from each component? The service manual can contain a way of outlining these tests. The inspections would include verifying you had not bypassed the cause or installed the problem. Your GM service department can assist if you get confused. The components, the things to inspect and verify, the tests and their readings? It can be simplified by an experienced tech. Last one like this I had was a little older and my foreman had a known good test part. I had no idea it was in the system.

1 of 1 people found this helpful.

You can find ways to research your make model and year for free using the automotive database and service manuals at the library. You can ask to read the ones in your dealers library. Technicians pass tests and earn their own set. Through GM, at least that's how it was when yours was new.

I have checked everything except change the gauge cluster and run voltage tests and the other tranny was doing the same thing


You can send the gauge cluster for repair thru dealer parts if the pinpoint tests lead you there. Without correct testing and process of elimination you are spending more than a correct diagnosis by GM......................When you change ecm's are you reusing your vehicles specified chip ? If there was no calculating governor in the system, the function could be there. Or in the cluster. This is why pinpoint testing is always performed before a part is thrown at it. They add up fast. Being a 94 and i dont have your book, you have to get that next.


By speed stepper, do you mean the part that calculates, governs, or translates?..............Terminology is important. Using the GM manual keeps you straight. I have seen some GM books in the city library reference section but not the county library. you still havent answered, what codes are stored? is there an MLP or TR sensor code about position of the manual valve? does the speed sensor you have in yours install by the differential ring gear or at the output of the trans? or does your rig have more than one ? gotta get that service manual, or read and photocopy as required.


Automotive database info was 25c a page last time I printed some. You may need a decent multimeter, at least as good as harbor freight has. read the speed sensor in mV. Inspect the other speed sensor and test it. if so equipped. Supplies and tools so far, plus the service manual info is less than the least expensive part, right?


Just read a thread where the guy calls it a VSB (speed buffer) says it is behind the glovebox, and behind a black plate with 4 screws. The VSB is white and has numbers on it to use when identifying. Theres 2 connectors. sounds like a speed governor, translator or calculator to me !........................ what a guess...................he has a 94 5.7L c/k 1500 wont upshift and speedometer inop. I would bet if you "checked everything" you missed that. possible?


Verifying the pinpoint tests is still the first issue unless you have a donor part to try. other threads discuss fuse trouble, relay trouble and sensor connection trouble. One guy says voltdrops in ignition harness, and another replaced his ignition switch. this is why the general writes the service manual. These dudes are all over it and know many possible ways to have your symptoms. Who knows what they're smoking, one guy had no 1-2 shift, then claims he fixed it with a 2-3 solenoid. I say run the tests in the proper order, do your research and buy the few tools. not part after part. jump down- turn around- blame some technician and call the wrecker. Or, you could get lots of little stuff at a yard if you keep on the way you were.


First read your codes and google them. do system prechecks again. Look them up if you dont know them or cannot find them on the computer. guess launching parts at it on somebody's guess drives me crazy, the GM dealer and library's just a few miles away.

Ok I do have the book and yeas when I said speed stepper I mention buffer And I have put 2 different ones in it

And I have read the codes and fixed those problems now all I get is code 12 system fine and I have done research on this issue and that is how I came up with the speed buffer ..... Also yes I am using my factory PROM/chip as u call it in the other ECM


That prom chip brainstorm was if the buffer was no longer in use.... so now you need the right readings on the wires as the diagnostic tries to simplify. The guy with the ignition switch voltage drops in the harness was saying pink and white. The other guy had found resistance thru his ignition switch I believe. Still others had fuse and or relay concerns not fully explained. mines older so I cannot compare. That's great you have a book for it, let me know if it is making sense now. The other thing discussed in threads i was reading was confusion about which speed sensor was for what. and test both. and power supplied to the buffer at the right volts. That's all I have about it. hoping guided diagnostic gets you to the component, wire, or connection at fault.


Imagine if you worked at GM and that was warranty....They would give you (.6 hr) for a diagnostic allowed. Those bastiges. Then you would have everybody howling like a monkey house. Good thing you can concentrate. Write more if you get confused, i suppose.


Some thoughts about bent connector pins and mice chewing the harness somewhere, pinched harness after trans replace, gang plug connector pins subject to water entry or vibration for 20+ years. fuses not thought of that could also be in use. like inline fuses or fusible links. These are all things I have had occur that wont be in the book. Theres a few more. But I will leave you to concentrate.


GM trucks from that era are famous for poor ground. no place to find ground, cab not well grounded bed the same. wreaks havoc with lights and body functions. You might try ohms to ground for the body, the engine, the neg post. The battery cable covers slide off if you pop/pry the bolts out. then you can be sure less than (.5 ohm) and the cover by the evaporator housing has lots of wires tucked under it too, inline fuses and grounds located there as well.


You could make a ground cable like an older toyota to solve. The cable has a leg. The leg goes to the fender, the cable goes to the frame then continues to the engine. a strap also comes off the head and goes under that evap cover to the firewall. if it is long enough you cut the insulation and crimp a locator bracket onto bare cable section then attach that to the frame. apply grease to protect. like a 75 corolla or something similar.


If you have a code 12 now, have you road tested it to reverify no upshift? and no speedometer ? seems like a sick trans that cannot upshift but will shift manually has to be electronically sick. That could mean a service bulletin could exist. during the "research" you have done, there were no outstanding recalls or bulletins that had applied to the issues?


Looked into your research and found Edmunds shows TSB # 468203 .........That also has a NHTSA #39297.................There is underdash wiring discussion, the bulletin was released just after that model year in 95 and applies to your 94 c/k 1500. I bet, if you need parts, the GM service counter already has them sitting, and service can hand you the bulletin or explain. Your library database is the other place you could check if you like that end of the horse.


I should have said the parts counter could have the bulletin part list. This is why you call one of the service advisors at the GM garage Or go there to discuss it. You can hear first hand from what fixed it from their memory or they can have the experienced tech tell you what you need to do. They know you dont want to tow it there or drive in first, but if it shifts manually they could do it for you or point to it. We did this all the time when I worked for GM. If it was hard for the customer to grasp the explaination we showed him a similar rig. If he had a warranty, we made an appt. If it was recalled, we ordered his part and agreed to call from his order slip. See how this works? They do it all day everyday. But the dealer I was with was the regional "fixer" of vehicles that were not getting satisfaction like they should. all our people were among the best.


Now you have me wonderin, if you just drove in there and stated the concern and it shifts manually, what would your time and materials be? (.6 hr) ? And customer pay plus parts? I personally have over an hour in squeezing my own head to remember what fixes that alone. Happy shifter.

It won't shift either way and I will give Gm a call and see what they say but I had it working and shifting just fine and then I changed the ecm back to mine to see if that was the problem and now back to square one so I think it's in the wiring so now I just have to spend the time and check it out


I noticed some harness companies selling small parts for wiring repair if there is a hardshell connector or some ends you need, Kwik wire and southern electrics specialists in your areas of concern if you cannot get it local or the dealer vendor. when I was there they had numerous drawers of little doo dahs that you would not believe. in tacoma, wa. I dont know if yours will be like them.


I tried reading that bulletin online, I have to buy into one of the sites or a database for automotive so that's as far as I can help from here i suppose.......but do keep reporting because I would like to hear if they have a fix or just want to do what you are having to do. You can pick my tsb number answer or the first one as helpful I suppose. or wait.

Dannyl it was bad wiring deep in the harness so it took a lot of cutting and replacing my friend and a lot of time


How do you describe bad ? melted, or chafed, shorted to power, shorted to ground, short between circuits, cut wire, corroded, disconnected, resistance in connection, poor fit, open circuit, bad crimp, inadequate splice, etc etc. because other reports were saying loss of voltage to vsb from ignition switch, harness or fuse, tcc fuse etc. are any of those true for your rig?

Best Answer Mark helpful

That southern electrics website offers pieces of the harness separately at low cost improved and corrective, they do not specify what job they are repairing. It would really be something if we could I.D. the harness at fault and have a goto plug in part replacing to connectors on each end. Then a guy could just google Kwk wire or whatever and select his by the picture and order it. Did the dealer have helpful advice to get you to the fix knowing your bulletin number? Did they let you read it? or how did you get there. just saw it? and went, oh schlitz? that's gotta be it !

Best Answer Mark helpful

The casing of the wires had been exposed to heat and were so bridle that u could twist the casing and it would crumble in ur fingers..... But as far as the dealer I didn't make it that far I just pulled the harness and examined it an cut out all of the bad and replaced them then plugged them back in and hit the key then took it for a test drive and she ran just fine my friend and I agree with the part where u said the quick repair plugs that would be super amazing lol


Thats how Ford TSB's and recalls work, they analyze and identify circuit repairs, then build a kit, then exclude everything you dont really need. then they send it out to all the dealers. thats in Ford parts. Then in motorcraft they offer similar more complete longer and thicker for as the age progresses the need. Then they have a complete repair at the ready and any motorcraft vendor can supply it to any parts who is wise enough to consult them later after years pass. The disease and the cure, just like an ex wife. That's why they call her mother Ford. It would be neat to have a simple section a connector at each end or the fuses at one end, then just install it. to fix a GM. First you need accurate reports. without them? That's why it gets more difficult and more expensive. So something cooked yours externally, not just 20 years, but fire? exhaust ?

I think just heat from the motor bc it was the part right between the firewall and the motor but I got er fixed now


That tells vo0lumes, you werent underdash near ignition switch, you were in the engine compartment wire harness above the trans but behind the valve cover and intake. so you had a baked set of wires going to the trans it sounds like. perhaps exhaust heat in the tunnel. you could use a reflective sheath for a prevent.


speed shops and exhaust specialists like pro max have insulation wrap or sleeves that expand. could be used to reflect the heat protecting against the baking of a catalyst in the vicinity. or just the header pipe/ y-pipe. heat produced under load.


When those were new, we were supposed to tie the harness up above the valve cover height and attach to a lifting bracket using a plastic tie strap..... hmmm. hadn't thought about that since like 92.

Lol I'll get some wrap to put on the but I'm glad that u could help and give me things to check out and from the sounds of it it took u back and u enjoyed helping me and believe me I appreciate it a lot


With your patience and resolve, you could do anything, i believe that. Your truck is lucky to have you.

Well thank u I really like my truck

i think i have the same prob i have the older 93 no speedo no one two shift some times no 12 volts to the tranny and some time it will some times the speed o will work and thin the tranny will shift will try the wireing harniss tomorrow thinks

have a 1997 5.7 vortec 4L60e trans..would sporadically go into limp mode,speedometer-tach-and red gear indicator light would quit working.Could restart engine and all would work for 500 yards or 20 miles and happen again.Found sEVERAL people saying they had same problem.I replaced ignition switch wiring harness from key switch to under dash.1 and 1/2 years ago.Still works.Did not replace key switch itself.Seems to be a common problem.Hope this helps someone.Drove me nuts

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