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Speedometer reads double

69superbee440
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69superbee440

69superbee440

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Been trying to solve my intermittent speedometer for awhile now. It is possessed  acts up under all different conditions speedometer will read pretty close to exactly double! Sometimes will do it frequently between drives other times can go a thousand miles without acting up. Shut the truck off and restart it’s all good. Checked wiring I found a repair on vss wiring but appears to be good. Replaced vss and inspected tone ring on diff. Speed on my edge matches speedometer when it acts up. Scanned and got code 74, 67, and 65. Should also add that truck has a 4w abs module but front hubs without sensor. I “fixed” this by tying front sensor wires into rear. Was acting up before I modified wiring (unless my memory is slipping which is possible) . I’m thinking ecm issue where it reads exactly double. Open to hear everyone’s thoughts. I’m sure there is lots that I checked that I’m not posting. What makes it worse is when it happens can’t do highway speeds because truck hits governor.

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Mopar1973Man

Mopar1973Man

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You need to return the front sensor where they belong. Then you most likely need to send the ABS module in to be rebuilt. Basically, the ABS module is a frequency counter. It measures the pulses per second and displays the speed on the speedometer. There is an issue with the rear sensor for sure being you got the 2 front tied to the rear sensor which is most likely fouling the ABS module ability to count frequency.

 

Module Master is $130 for the rebuild and has 5-year warranty. I've had my module rebuilt by them and excellent people. 

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69superbee440

69superbee440

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30 minutes ago, Mopar1973Man said:

You need to return the front sensor where they belong. Then you most likely need to send the ABS module in to be rebuilt. Basically, the ABS module is a frequency counter. It measures the pulses per second and displays the speed on the speedometer. There is an issue with the rear sensor for sure being you got the 2 front tied to the rear sensor which is most likely fouling the ABS module ability to count frequency.

 

Module Master is $130 for the rebuild and has 5-year warranty. I've had my module rebuilt by them and excellent people. 

 

I would prefer to leave abs rigged up the way I have it (if possible) because it will never come on if all wheels are always doing the same speed. Personally I don’t like the earlier abs systems. I should add I have disconnected front sensor wiring while it’s been acting up with no change. I am pretty confident issue popped up a couple times before this modification as well. At this point I think it can only be either The abs module or pcm. Thank you for the heads up on the module master folks! I might even reach out to them to see if they have heard of this kind of issue with those modules.

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Mopar1973Man

Mopar1973Man

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23 minutes ago, 69superbee440 said:

The abs module or pcm.

 

ABS module.

 

PCM doesn't control speed data. The only thing PCM is doing is starting the CCD network. The PCM gets the CCD network going and ABS module calls out on the network its speed data. The PCM receives the data for transmission and cruise control. The ECM receives the data as well for controlling the grid heater cancel at 25 MPH. The gauge cluster receives the data as well for displaying speed. 

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69superbee440

69superbee440

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9 minutes ago, Mopar1973Man said:

 

ABS module.

 

PCM doesn't control speed data. The only thing PCM is doing is starting the CCD network. The PCM gets the CCD network going and ABS module calls out on the network its speed data. The PCM receives the data for transmission and cruise control. The ECM receives the data as well for controlling the grid heater cancel at 25 MPH. The gauge cluster receives the data as well for displaying speed. 

Awesome info thank you! more or less narrowed down to abs module. I agree with you on my front abs sensor bypass makes me suspect it other than it still acted up. I sent an email off to module masters to see if they have heard of a failure like this. What makes me really suspect the module itself is shutting truck down and restarting it fixes it. 

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Mopar1973Man

Mopar1973Man

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4 minutes ago, 69superbee440 said:

What makes me really suspect the module itself is shutting truck down and restarting it fixes it. 

 

That's because when you do shut down or even key off and back on while rolling resets the ABS module in flight. If there is an error or issue the key off and on again will cause the ABS module to reboot into the network again.

 

Another thought is excessive AC noise can and will affect the reporting nature of the ABS modules speed sensors.

 

 

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69superbee440

69superbee440

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Hopefully I hear back from module masters first of the week to see if this is an issue they have seen and if they can correct it.

5 minutes ago, Mopar1973Man said:

Another thought is excessive AC noise can and will affect the reporting nature of the ABS modules speed sensors.

 

I did a a/c test when I was having my dead pedal issue seemed within in spec. When I get some free time I am going to do ground mod you suggested.

 

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Dieselfuture

Dieselfuture

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1 hour ago, Mopar1973Man said:

 

ABS module.

 

PCM doesn't control speed data. The only thing PCM is doing is starting the CCD network. The PCM gets the CCD network going and ABS module calls out on the network its speed data. The PCM receives the data for transmission and cruise control. The ECM receives the data as well for controlling the grid heater cancel at 25 MPH. The gauge cluster receives the data as well for displaying speed. 

I suppose it would be possible that my abs module is faulty and triggering random ABS brake light on and not the wheel bearing itself or a front sensor

20181123_143746.jpg.775763cf9737e08b2e85a73542465e61.jpg

 

:hijack:

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69superbee440

69superbee440

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I have been thinking about making new wiring with a drill to go right from abs module to vss because the old wiring does have some repairs. That being said I would anticipate a no speedo issue from any kind of wiring issue not it reading exactly double! Just thinking out loud again....

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69superbee440

69superbee440

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15 minutes ago, Mopar1973Man said:

All speed sensor wiring must be twisted pair. There have to be a particular number of twist per foot for shielding reasons. 

Absolutely that was my intention with the drill. I have had good success in the past making abs wiring like this. Still don’t think it will solve my issue though.

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