Speedometer reading VERY high

Ben Mechanic Chesnee, South Carolina Posted   Latest   Edited  
Resolved
Electrical
2000 Ford Ranger XLT 3.0L (U) 5-spd (5R55E)

We put a reman 5R55e in this truck and nothing else. Now the speedometer ramps up to 100mph just idling in reverse or drive. In drive this causes the transmission to immediately shift up to 4th so the PCM is seeing the same as the speedometer. 

The only speed sensors on this thing is the ABS sensor in the third member and a turbine speed sensor inside the transmission. The turbine sensor reads input RPM just fine. The vehicle has only rear ABS.

We unplugged the transmission to no effect. Unplugged the RABS to no effect. Unplugged the alternator too, nothing. Asked the installer what else he might have disturbed and it was only the driver's O2 sensor he said. Unplugged that just for kicks, no change. All the data available from the transmission and engine appear to be normal other than the road speed reading.

There is a speed sensor test port at the RABS unit where the rear speed sensor's output can be read. With a multimeter and the truck turned off we spun rear wheels by hand and got about the specified 200 millivolts. I found no other spec than that. 200 is expected at about 3mph. When the truck is cranked up, put in gear, and allowed to idle the speedo rockets up to 100 mph and the amps read 2.1. Perhaps correct for the speed but it's just idling. 

We had another truck handy and swapped the sender to no avail. At this point we are starting wonder if the GEM magically sprung. The speedo signal goes from the sender and is split between the GEM and RABS ECU's. From the GEM the signal goes to the PCM and speedo head. 

The truck was test driven driver by two people before being taken in and both say it wasn't doing this before. Customer says he hasn't seen this.

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
   

Is there a knob to switch it between 2H / 4H / 4L ? If yes, do speedometer values change when the knob is switched from 2H position? [Ben replied below that there are no 4L or 4H buttons.]

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Henry Owner/Technician
Southampton, Pennsylvania
Henry Default
 

Look for places where lifting the vehicle may have disturbed a wiring harness. We've had weird issues occur on E-Vans after lifting. Also, corrosion in the PCM or grounds to it. Again, we've had these issues with older E-Vans, no first hand knowledge about Rangers.

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Tom Engineer
Claremont, California
Tom Default
 

Hi Ben, Can you tell me what vehicle this is for, if it's not an F-100? I do see quite a few non-F-100 2000 rangers available for selection. Our vehicle data comes from the AutoCare Association, so I can file a report if there's an issue, but doing some searching, I'm seeing quite a few references to 2000 Ford F-100 Rangers. Perhaps outside of the US market.

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Matt Educator
North Canton, Ohio
Matt Default
 

I would get a lab scope on the signal to see if you are getting any voltage spikes. I had a Cadillac that did something similar. MPH on the speedo would go to 80 at an idle in park. I found interference from a spark plug wire feeding back into the VSS harness.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

It's a 2000 Ford Ranger XLT 3.0 (U) 5 speed (5R55E) . In the US the last F100 was the full sized half ton pickup. After 1982 the smallest of such was thereafter called an F150. In the 1970's and early 1980's there was available a "Ranger" trim package on top of being an XLT. That option disappeared (I think) at about the same time the smaller Ford Rangers were introduced in 1982. To avoid model…

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Tom Engineer
Claremont, California
Tom Default
 

OK, thanks for the info, I will look into this with AutoCare. In the meantime, I updated your question to use the vehicle you mentioned and removed references you made to the invalid vehicle to avoid reader confusion going forward.

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Tommy Owner/Technician
Holly Ridge, North Carolina
Tommy Default
 

If it wasn't miss firing before the work was performed, I would go in the speed error direction. Many manufacturers have speed limiting in the software that will mimic miss fires. I have had failing speed sensors trigger miss fires, and the speedometer read correctly.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

It was misfiring when checked in and noted on the work order. So it was misfiring prior to this speed sensor issue. We find this running condition fairly typical for high mileage Ranger 3.0's around here. It was honestly a bit surprising the owner decided to up the money for a reman transmission in this one. It's not actually a terrible truck but....

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Tony Owner
Peoria Heights, Illinois
Tony Default
 

Was their a PO340 for the cam sensor in the codes? I know you said you disconnected the alternator but if it was a 3 wire alternator you would have to pull the battery connection not the pigtail to keep it from charging.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

No P0340 now or when it came in. It did have P0503 for Intermittent VSS though. The alternator looks to be a 4G (or maybe a 3G?) so I pulled the main plug on it to disable it. I didn't pull the smaller Stator plug though.

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Michael Technical Support Specialist
Milwaukee, Wisconsin
Michael Default
 

If you unplug the transmission does the speed signal drop to zero?? There are 2 speed sensors in the system one is the turbine shaft speed sensor (internal) and it should have an out put speed sensor on the t-case.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

Being 2wd makes it not have a transfer case and again, there is no OSS in any case. "We unplugged the transmission to no effect. "

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Chris Technical Support Specialist
Commack, New York
Chris Default
 

From the diagrams I looked at I also see the speed control servo has this wire as well. In the late build it also shows a belt minder module on the circuit as well. Have you checked with the speed control servo disconnected? If this vehicle has a belt minder module it would be in the dash above the ashtray. Have you checked the GEM pids for VSS data or DTC's?

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

The GEM doesn't have a VSS PID, not on our Zeus anyway. Odd, considering how the VSS signal appears to be wired through it be wired through it before going to the speedo and PCM. This truck does not have cruise. It had four GEM codes, door ajar light, LF window "one touch" relay, seat belt lamp, and B1359 Ignition run/ACC circuit. I believe it does have the belt minder. There's a gaping hole…

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Jj Technician
Quincy, Massachusetts
Jj Default
 

It looks like the GEM might be applying some kind of signal conditioning/processing to the raw analog input of the RABS sensor. I'd be curious to see what is coming out of the GEM on pin 1, the gry/blk wire, because that is the signal that goes to the PCM and cluster. I would think if it's pulled high or low by a module or a short it could easily give false VSS input. Does the PCM have a VSS PID?

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

I've been looking at the wiring diagram section like what Mr. Rivera posted up below. As you can see, if you unplug the RABS box (like I have) then the speed sensor is basically a direct line to the GEM. Mr. Snyder above a post is seeing some wiring I have not (yet). What's on the GEM's output line and where exactly it goes next I expect. The PCM's VSS PID is right in line with what the speedo…

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Jj Technician
Quincy, Massachusetts
Jj Default
 

Yeah, it sounds like the input to the GEM is fine. You'll find that the GEM VSS output on that gry/blk wire in pin 1 is the PCM VSS input and the cluster input. It runs out to the PCM under the hood, which is the only place I can figure something would have happened while installing the transmission.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

What diagrams? If you don't mind me asking. I am using Alldata and focused on the RABS section and didn't see that. Alldata has a wonderful big stack of diagrams for this thing but they are very unhelpfully laid out by "number". So I have to look at them one by one to see what they are unless I back up somewhere to instrument cluster repair info or something. Time is running out for today.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

Usually in All-Data you would start in the Instrumentation section and then find speedometer, and then the wiring diagram for that would (usually.....hopefully?) show any splices and reference the OTHER diagram numbers where the lines go off.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

I've been working from the tail of the truck forward because the most likely suspect is that the installer caused this issue somehow. Versus one of those weird spontaneous failures. And juggling a shop load of work. Somehow I forgot I can simply open Alldata in another tab at look at the cluster. That way not backing all the way out of my RABS system references. Brainfart. Like I don't have a…

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Douglas Manager
Las Vegas, Nevada
Douglas Default
 

Check the grounds

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

Have one in mind I might have missed?

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James Technician
Savannah, Georgia
James Default
 

Looks like G201 provides the ground for the speedomter and cluster, along with the GEM, RABS, DLC, etc.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

Voltage drop test said it was good but we can check it again. Incidentally the RABS diagnostic plug is supposed to be at that same area but isn't. Yay service info.

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James Technician
Savannah, Georgia
James Default
 

Just out of curiosity have you checked that the harness running down behind the engine to the trans wasn't pinched when the Trans R&R was done? Doesn't have to still be pinched, just crushed can cause problems.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

Sure. A primary focus. With a 3.0 you have to "wedge" the transmission in and out past a transmission tunnel lip unless you want to pull the exhaust, Which we don't. The transmission harness runs right across that trouble area. It so happens I assisted the guy taking the transmission past that lip both in and out and clearly recall making sure the harness was out of the way. Popped the conduit…

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Juan Diagnostician
Monclova, Mexico
Juan Default
 

I would check the line of sesnores and the gen module and also check the charging system on a Dodge Caravan the speedometer moved a lot at low speed and the problem was the alternator

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Robert Diagnostician
Fair Oaks, California
Robert Default
 

I dont know if you disconnected the RABS to eliminate that module from the circuit. could be putting noise on circuit. I would be looking at grounds on rear of engine that may have been bolted to trans bell housing and not reconnected. modules without a ground maybe trying to ground through the speed sensor circuit.

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Ben Mechanic
Chesnee, South Carolina
Ben Update
   

Took opening four tabs of wiring diagrams. Aftermarket color diagrams are easier to read but misleading. One shows four VSS leads. Out to speedo, two in from the rear axle and a fourth one vaguely labeled VSS also on pin 9 with one rear axle input. Turns out that RABS and ABS trucks are very different. An ABS truck takes the two wire rear axle signal into the ABS ECU only. That ECU then outputs…

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Stephen Technician
Gallatin, Tennessee
Stephen Default
 

For the GEM to “make up” and output a signal that will fool the speedo seems very strange. I would want to isolate the source of the signal before condemning a the GEM. What is the source of the speed signal into the GEM? ie; a sensor, data bus?

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Chris Technical Support Specialist
Commack, New York
Chris Default
 

The Rear speed sensor reports to the GEM (w/RABS) and then broadcasts the vss on a single wire output to the PCM, IPC, Cruise Module, and Belt Minder(if equipped). The GEM module shows as having a VSS_GEM pid in the service information. I am not sure if that is the input VSS or the Output VSS. Without Cruise control there may still be a 10? pin connector for the cruise servo/module. Monitoring…

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

When the RABS ECU is unplugged (as I have stated we have done) it's basically a straight shot. Two wires from the rear differential speed sensor (that generates an AC voltage) straight to the GEM. There is a dead end branch plug at the RABS unit itself but it is unused. Very convenient for reading the VSS signal discretely though as it provides the same signal as going under the truck and…

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Jj Technician
Quincy, Massachusetts
Jj Default
 

I think your concern is in the GEM VSS output, the GEM sounds like it's input is ok from the RABS sensor. The concern now is if that GEM VSS output is being affected by a short or another module on that particular circuit, or if it's just the GEM itself causing the problem. I would scope pin 1 at the GEM, gry/blk wire, with it both plugged in and unplugged. If the signal is only wonky with the…

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

Not sure why this one is stuck in my head, maybe because a 2000 Ranger is a typical truck out here. Just wanted to mention I am pretty sure the GEM is programmable. With an NGS (the old Ford handheld) you should be able to set if the GEM is 4wd and what the axle ratio is etc.

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Chris Technical Support Specialist
Commack, New York
Chris Default
 

I think most of that were on the green cards.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

I got a full unused NGS-XL set straight from Hickock two years ago. They were collecting dust in the back room. :-) Only cost me like $700. Couldn't pass it up!

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Ben Mechanic
Chesnee, South Carolina
Ben Resolution
 

Well, not my preferred resolution as I still have no clue as to how or why but a replacement GEM finally came in and immediately fixed the issue.

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Resolution
Chris Technical Support Specialist
Commack, New York
Chris Default
 

Solved by process of elimination. Ford's preferred diagnostic method. Check everything else if its good throw a module at it.

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Ben Mechanic
Chesnee, South Carolina
Ben Default
 

Sounds about right actually. I consider it repaired to the customer's satisfaction but not to mine. I did take a look at the misfire. Took about three minutes to isolate it to one cylinder where I found a cracked plug insulator. Odd. New plug, runs better, and the customer just picked up. Happy to have his truck, noted that it seemed to run a lot better (Shhh!) and he's gone with it.

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