Author Topic: Speedo sensor and Tach sensor both failing at the same time?  (Read 614 times)

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Offline Papa Dave

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Speedo sensor and Tach sensor both failing at the same time?
« on: October 18, 2019, 07:51:07 PM »
Background - 2005 Winnebago Journey with Freightliner chassis, Cat C7, and Allison tranny.  Completed 4000 mi trip during which I would occasionally notice that both my tachometer and speedometer gauges would be "jumpy/twitchy" instead of steady/smooth.  Took the coach to a mechanic to scan for any new codes.  Immediately after pulling the codes both the speedo and the tach gauges ceased to work.  The mechanic has told me that both sensors likely have failed and wants to replace both before doing anything else.  This seems like a remarkable coincidence that both sensors would fail at the same time.  Aren't these sensors in very different locations?  Is there another problem that would cause both the speedo and tach gauges to cease functioning at the same exact time besides simultaneous failure of both sensors?

Offline Ken Carpenter

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Re: Speedo sensor and Tach sensor both failing at the same time?
« Reply #1 on: October 18, 2019, 08:11:51 PM »
Welcome to the Forum. Call Freightliner help desk 1 (800) 385-4357.
2005 Winnebago Journey 39K, C7 350HP
Jeep Grand Cherokee, Airforce One
Diesel RV Club Officer & Board Member

Offline David.e.atherton

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Re: Speedo sensor and Tach sensor both failing at the same time?
« Reply #2 on: October 19, 2019, 04:24:44 AM »
PapaDave, it very unlike that both sensors failed and sounds like you drove the motorhome
to service shop the answer would be no. The sensors are located ( both ) behind Heui pump .
Held in place by metal clip. Can be replaced without removing the Heui pump. The tact is
Located back on rear of engine on bell housing. Can you email me your engine Serial number.
Your problem is minor.   Ask Dave, Dave Atherton Retired Cat amechanic

Offline Papa Dave

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Re: Speedo sensor and Tach sensor both failing at the same time?
« Reply #3 on: October 22, 2019, 09:04:02 PM »
Hello David.  My C7 serial# is 10P83F285788. 

I have been in touch with Freightliner Custom Chassis and a very helpful tech there agrees with you.  He explained that all the gauges in my dash have identical, and interchangeable, signal cable connectors.  Since other gauges seem to be working, and all the gauges receive info from the C7 ECM, he suspects that one of the gauges is bad.  He also said that a bad gauge can corrupt the data needed for another gauge.  So if the tach gauge is bad, it could cause the speedo gauge to malfunction, or vice versa. To troubleshoot further he asked me to move the signal connector from a working gauge to the tach or speedo, unplug the other gauge (tach or speedo), and test.  By swapping and testing different signal connectors with different gauges, I should be able to see if the issue is with a gauge or with the wire/signal harness connecting to a gauge.