Intermittent Oil temperature displayed

[Dusty]

If the sensor is reporting an out-of-range temperature, even if it's false, the PCM should be declaring some sort of oil message and/or a check engine illumination. I believe you wrote that the cluster eventually displays a - - - - for oil temp. That could mean the PCM can't display an out-of-range value, the PCM doesn't have a value to report, the cluster is defective or not receiving a value at all.

Here is where a good diagnostic tool that looks at the actual oil temp signal would come in handy.

However, as others have indicated, I do not trust aftermarket electrical components or those where authenticity cannot be determined. Check back when you have installed the OEM part.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 151830 miles.

 

[GaParker]

okay, I got the OBDLink MX+

It says the sensor voltage is jumping around a lot between 0.4 volts and 0.6 volts when the oil temperature hits 135 F (which is not right, that should be a very steady voltage). When it goes to -- MX+ says it's about 0.4 volts.

So. I guess we're back to the sensor probably came from Advanced AP and isn't OEM, and is flaky at temps above 130 F. The actually OEM sensor should be here in the next few days and I'll swap it out and see what happens then.

I don't know why MX+ shows a voltage that disagrees with what I measured with a dvm, but so much has happened since I made those measurements...

I'll get back when I have the new sensor installed.

Thanks

 

[GaParker]

Oh, MX+ also displays the digital oil temp, and it agrees with the Instrument Cluster displayed temperature. Although it goes to -40 C when the display goes to --

Assuming it's reading the value from the CAN bus that would say the ECM is getting a sensor voltage it doesn't like (i.e. flaky, jumpy, 0.4v) or voltage that's out of range (like 0.4v).

I'll get back to you.

 

[04fxdwgi]

Jumping around like that indicates wiring problems or possibly a bad ECU. The voltage coming to your sensor should come off the common buss in the ECU and varying output from sensor is actually what you are reading at the OBD / the ECU is reading.

Check all your wire harness and connections for tightness, corrosion, loose pins, indications of abrasion or critters chewing on it.
Have you had any harness connectors apart lately? Pull harness plugs off ECU and check for problems and clean with contact cleaner.

Again, any actual problem should have tossed a CEL.

 

[GaParker]

Problem solved.

Well. I got the new OEM oil temp sensor, and it is physically identical to the failed one. Except, the new OEM sensor doesn't fail. I've driven the truck several times now (not towing), and the oil temp maxes out about 222F. So it certainly appears to be 'fixed'.

I took data on both sensors by putting them in an oil bath and measuring the sensor resistance vs temperature. They both plot normally, with essentially the same resistance data over the range of 90F to 340F.

The resistance at 212F (for both sensors) was 1000 ohms. The resistance is linear when plotted on a log scale (which one would expect).

I expected the 'failed' sensor to not graph nicely above the temp that it fails in the truck, but it didn't do that, it behaved like the 'good' sensor.

So, it may be that the sensor has to be loaded to fail, i.e. a DVM may not put enough current through the part for it to fail. I suppose I could take it out to the shop and put it on a power supply to test that idea. But not today... I'm tired now.

Anyway, here's the data for those who are curious.

 

[04fxdwgi]

The connection could have been dirty or has some corrosion on it and disconnecting it may have improved the connection problem.

Not uncommon to see this.