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BAK · 03-07-2020, **(Subject: No power to speed sensor )**

I have no power to speed sensor, the wire is good all the way to ECM, any idea what else to check? this is a 2012 388 X15 cummins, could it be in the ECM

Lonestar10 · 03-08-2020, **(Subject: No power to speed sensor )**

any special tuning? if so could have gotten turned off. how have you diagnosed the wire being good? seeing 5v-12v on a multimeter doesnt mean the wire can carry current.

BAK · 03-08-2020, **(Subject: No power to speed sensor )**

(03-08-2020 )Lonestar10 Wrote: any special tuning? if so could have gotten turned off. how have you diagnosed the wire being good? seeing 5v-12v on a multimeter doesnt mean the wire can carry current.

no special tuning, speedometer quick working, changed speed sensor, still didn't work, checked at the sensor with key on and had no 5volts , checked where it comes out of ECM, nothing there, wire going to ECM is good, wondering if ECM is the problem

Rawze · 03-08-2020, **(Subject: No power to speed sensor )**

Register your engine/truck on quickserv.com (free) -- look up the wiring diagram for the ecm and it will tell you how and what is wired to the ecm.

What make/model truck?
What version of the ISX? (CM2250? CM2350-X101?)

-- Also, just because the speedo stopped working does not mean its the speed sensor. Peterbilt and KW's are notorious for speedo in the dash to stop working properly, it is a common failure for them.

some notes: Not sure it applies to the ISX specifically, but something to consider ...
Many types of speed sensors do not even need to have a voltage going to them. Speed sensors can often use what is known as "variable reluctance magnetic sensing principle". This means it generates an alternating voltage (like an alternator does but on a much smaller scale) when the tail shaft is turning/moving and the ecm reads this, measures its frequency like a magnetic pick-up coil similar to reading the music on a cassette tape. If it is one of these types of sensors, there will not be anything coming out from the ecm that can be measured.

just some other things to consider/think about.

Mattman · 03-08-2020, **(Subject: No power to speed sensor )**

Does the odometer work?
Lots of speed sensors create their own signal. Not sure how paccar does it.

snailexpress · 03-08-2020, **(Subject: No power to speed sensor )**

(03-08-2020 )BAK Wrote:
(03-08-2020 )Lonestar10 Wrote: any special tuning? if so could have gotten turned off. how have you diagnosed the wire being good? seeing 5v-12v on a multimeter doesnt mean the wire can carry current.

no special tuning, speedometer quick working, changed speed sensor, still didn't work, checked at the sensor with key on and had no 5volts , checked where it comes out of ECM, nothing there, wire going to ECM is good, wondering if ECM is the problem

My gueass you are checking road speed sensor located on tranny rear? Should be no voltage to the sensor, sensor is magnetic, create pulses.
Or you have problem with engine speed sensor?

Signature620 · 03-08-2020, **(Subject: No power to speed sensor )**

When dealing with vehicle speed sensors, it's important to know what sort of truck is involved. Some run 2 sensors - 1 for the ECM and 1 for the speedometer. Some trucks run 1 sensor to the gearbox controller, then the cab and ECM read it on the data link. Some run 1 sensor to the ECM and the body control module read it on the data link.

If the sensors are inexpensive, I'd try changing it and inspecting the pins on the connector. If it's the adjustable type - Turn it all the way in and 1/2 turn out (they are often very easy to break if the locknut is over tightened). If that doesn't work, you'll need to chase the wiring and potentially start looking at changing the speedometer itself.