Speedo Malfunction
Thread Starter
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Mountain Pass
Joined: Mar 2007
Posts: 163
Likes: 9
Speedo Malfunction
After I repacked my front wheel bearings I went for a test drive and the speedometer wouldn't show over 32 mph. The tach and other gauges work fine and the truck runs well, just a faulty reading on the speedo. I pulled out my trusty tablet and checked for codes with both Forscan and Torque Pro, nothing other than a windshield washer error and a brake center antilock rear wheel speed sensor error both of which have shown up for years.
I took it for another test drive and ran TP to check out speed, rpm, EOT, and all the other readings on my TP dashboard. All read normally with the exception of road speed which read the same as the speedometer gauge.
When I got back I crawled under it and checked the connection to both tranny speed sensors (auto rebuilt within the last 2 years, both replaced at that time), both connections were clean and tight.
Any ideas before I start pulling the instrument cluster?
I took it for another test drive and ran TP to check out speed, rpm, EOT, and all the other readings on my TP dashboard. All read normally with the exception of road speed which read the same as the speedometer gauge.
When I got back I crawled under it and checked the connection to both tranny speed sensors (auto rebuilt within the last 2 years, both replaced at that time), both connections were clean and tight.
Any ideas before I start pulling the instrument cluster?
Got Data?
Joined: Dec 2012
Posts: 4,239
Likes: 1,369
From: Lake Stevens, WA
I would not think the cluster is the issue if you are seeing the road speed on the OBDII via TP or FORScan reading the same as the speedo.
My speedo would read correctly even though the VSS sensor was bad, though I had an antilock brake warning light and associated code. Was guessing the PCM was getting speed data from the front antilock brake sensors, or maybe turbine shaft/output shaft sensors, but not sure.
You have a 2000 - does it have front ABS sensors? Was wondering of one of them might have come unplugged or otherwise disabled during the front wheel pack.
What are the specific codes you get? Troubleshooting that rear wheel speed sensor error is not too bad. In my case, it was the VSS sensor, confirmed by checking the resistance of the sensor (was open circuit).
My speedo would read correctly even though the VSS sensor was bad, though I had an antilock brake warning light and associated code. Was guessing the PCM was getting speed data from the front antilock brake sensors, or maybe turbine shaft/output shaft sensors, but not sure.
You have a 2000 - does it have front ABS sensors? Was wondering of one of them might have come unplugged or otherwise disabled during the front wheel pack.
What are the specific codes you get? Troubleshooting that rear wheel speed sensor error is not too bad. In my case, it was the VSS sensor, confirmed by checking the resistance of the sensor (was open circuit).
Thread Starter
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Mountain Pass
Joined: Mar 2007
Posts: 163
Likes: 9
BWST,
I'll have to check on the front wheels for an ABS sensor, I had to replace one hub/rotor assembly due to an outer bearing race that had wallowed out the hub, the new part looked identical to the old one. I didn't think to check, I was in a hurry as usual, I just assumed they were only on the rear. I had a VSS trouble code last year and replaced that sensor even though it didn't test bad. It turned out the alternator was failing and creating noise in the circuit causing my erratic shifting problem.
The only codes are B1450 & B1438 (Wiper selector switch circuit failure) and C1250 (Wheel speed sensor rear center input- Antilock brake system), all three of which have been on for quite a while with no ill effects. The wiper switch and wipers work fine. As far as the C1250 goes I have no idiot lights that illuminate and the truck stops straight and true even when towing.
I'll have to check on the front wheels for an ABS sensor, I had to replace one hub/rotor assembly due to an outer bearing race that had wallowed out the hub, the new part looked identical to the old one. I didn't think to check, I was in a hurry as usual, I just assumed they were only on the rear. I had a VSS trouble code last year and replaced that sensor even though it didn't test bad. It turned out the alternator was failing and creating noise in the circuit causing my erratic shifting problem.
The only codes are B1450 & B1438 (Wiper selector switch circuit failure) and C1250 (Wheel speed sensor rear center input- Antilock brake system), all three of which have been on for quite a while with no ill effects. The wiper switch and wipers work fine. As far as the C1250 goes I have no idiot lights that illuminate and the truck stops straight and true even when towing.
Thread Starter
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Mountain Pass
Joined: Mar 2007
Posts: 163
Likes: 9
As Homer would say- DOH! On inspection the new rotor isn't fitted with the antilock ring so of course the sensor has nothing to read. I measured the rotor faces, compared rotor overall heights and diameters, checked rotor widths, but totally missed the lack of the saw-tooth ring in the center of the hub. The older I get the more amazed I am by my lack of observational abilities.
Thanks for holding my hand and gently guiding me back to the light.
Thanks for holding my hand and gently guiding me back to the light.
Got Data?
Joined: Dec 2012
Posts: 4,239
Likes: 1,369
From: Lake Stevens, WA
Glad you found this. I have not seen how the 2WD ABS works on these rigs. Homer speaks for all of us at times with an appropriate word.
So a rotor swap for the sawtooth ring version should do it, sounds like. Good deal.
So a rotor swap for the sawtooth ring version should do it, sounds like. Good deal.
FTE Leadership Emeritus
Joined: May 2014
Posts: 27,345
Likes: 5,941
From: Lake Hartwell, GA
I have a 2000 F-250 XLT 4x4 with 2 wheel ABS. @FordTruckNoob has a 2000 F-250 XLT 4x4 with 4 wheel ABS. Our trucks were only a few months apart according to the build date. My ABS sensor wires are cut at the hub and the connector is left in there to be a seal. His are connected and function according to the ABS module.
I have the weird T-fitting for the brake fluid in the driver side wheel well, FTN has a normal pass through fitting for the brake fluid.
Lewis, it seems you have figured out your issue and I am glad to hear that. I was just about to open up the Ford manual and see what the symptoms of a failing speedometer were.
Keep us updated sir.
I have the weird T-fitting for the brake fluid in the driver side wheel well, FTN has a normal pass through fitting for the brake fluid.
Lewis, it seems you have figured out your issue and I am glad to hear that. I was just about to open up the Ford manual and see what the symptoms of a failing speedometer were.
Keep us updated sir.
Thread Starter
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Mountain Pass
Joined: Mar 2007
Posts: 163
Likes: 9
Just an update: the new rotor with the antilock ring fixed my problem. Evidently the speedo relies on the front rotors for it's inputs on 2wd trucks with 4 wheel antilock systems. I'll files this obscure bit of info away for future troubleshooting.
Well back into the furnace. A dead tree fell on a fence-line last night so I get to play with my chainsaw and other toys, the joys of ranching never quit.
Lewis
Well back into the furnace. A dead tree fell on a fence-line last night so I get to play with my chainsaw and other toys, the joys of ranching never quit.
Lewis
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Got Data?
Joined: Dec 2012
Posts: 4,239
Likes: 1,369
From: Lake Stevens, WA
Another good data point on our trucks using these sensors for the speedometer. I purchased my truck with the VSS broken, yet the speedometer worked fine. Tells me even for 4wd trucks with 4 wheel antilock, the front sensors are used for this function.
Glad you are back in business.
Glad you are back in business.
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