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Thepimentals
Active Member

20 Posts

Posted - 09/10/2022 :  06:33:40 AM  Show Profile  Visit Thepimentals's Homepage  Reply with Quote
Hello. My mbe926 on my Thomas hdx is having a low voltage issue on the coolant temp sensor. Iím only getting 3.08v I tested the ground and thatís fine. So I replaced the wire from the ECM to the sensor and Iím still getting the same voltage. Is this now and ECM problem? Any other ideas? I do have some active engine codes im not sure could be related.
Sid 155 fail 00
Sid 035 fail 07
Sod 155 fail 02

40ngone
Senior Member

USA
164 Posts

Posted - 09/10/2022 :  08:25:03 AM  Show Profile  Reply with Quote
I do not have any prints for this engine, but I would ask this. What is the voltage supposed to be. 5v reference or 12v. Is it 3.08v at the connector when it is disconnected from the sensor, or still connected to the sensor.
If sensor is disconnected, it should pull up or down depending on if it is a pull up/down circuit. If it is with the sensor disconnected, and still reads 3.08v coming out of the ECM, if it were me, I would check ECM grounds and powers going in to the ECM. All that I just said is just a generic approach. I would study the schematic, and be cautious.

One other thing to clarify. Is the 3.08v at the reference terminal, or the signal terminal?

Edited by - 40ngone on 09/10/2022 08:27:29 AM
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Thepimentals
Active Member

20 Posts

Posted - 09/10/2022 :  3:00:14 PM  Show Profile  Visit Thepimentals's Homepage  Reply with Quote
Iím reading that voltage at the sensor plug while unplugged from the sensor. Itís supposed to be 5v and my coolant level sensor tested the same way is 5v. I also tested the ground wire at the temp sensor plug and that reads normal too so itís a power issue as far as I can tell. I just canít figure out why. Itís only a 2 prong plug so its 2 wire. Negative and positive.
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Bluenozer
Top Member

Canada
615 Posts

Posted - 09/12/2022 :  11:09:02 AM  Show Profile  Reply with Quote
most of 5v sensors feed more than one sensor , does this share the 5v with another sensor( are the other codes for another sensor) if not then the 5v would come from ecm , and if it is not then ecm must be bad internally

OEM trained in wiring and all engine platforms for over 20 years
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Thepimentals
Active Member

20 Posts

Posted - 09/14/2022 :  11:50:10 AM  Show Profile  Visit Thepimentals's Homepage  Reply with Quote
Itís direct from the ECM.
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40ngone
Senior Member

USA
164 Posts

Posted - 09/14/2022 :  1:51:59 PM  Show Profile  Reply with Quote
It would really help to have a full schematic of the computer data system for this application. But to go back to what direction Bluenozer was headed(I think).
If all the other 5v references coming out of the ECM are good and show no signs of being goofy, and if any external 5v splice to another sensor then it very well could be the ECM. If any other 5v reference has any voltage anomalies, I would disconnect that circuit and see if your ECT voltage comes back. Last call ECM.
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Bluenozer
Top Member

Canada
615 Posts

Posted - 09/15/2022 :  11:20:42 AM  Show Profile  Reply with Quote
looks like it shares ground signal with 4 other sensors , does not share power with any sensors

OEM trained in wiring and all engine platforms for over 20 years
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Thepimentals
Active Member

20 Posts

Posted - 09/18/2022 :  2:56:57 PM  Show Profile  Visit Thepimentals's Homepage  Reply with Quote
Right it does share a ground wire but I tested the ground on the Ect sensor with other varying voltage locations on the bud and they were all to spec so that ground must be good?
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Thepimentals
Active Member

20 Posts

Posted - 05/30/2023 :  1:45:08 PM  Show Profile  Visit Thepimentals's Homepage  Reply with Quote
I did just want to update that Iíve not figured this issue out yet. I have found that the fuel level sensor has the same voltage as the coolant sensor. I cannot find an accurate wiring diagram for this engine. The colors for the sensors donít match any schematics Iíve found.
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