Thermistors

Hello All-

In regards to thermistors- I understand the concept of PTC when the temp rises, resistance rises and NTC when temp rises, resistance decreases. My question is- can you tell if its PTC or NTC by looking at it or testing it? Or am I just going overboard with the thought?

Thanks,
MrMike

You could unplug them and see if the temperature goes high or low. NTC 5v will be a super low temperature and PTC will be super high, best I have, or maybe read the theory and operation.

Can't think of a way to distinguish between the two by visual alone... You could always change the temperature of whatever the thermistor is measuring and monitor the resistance/voltage.

Otherwise, I think theory and operation is your best bet, like AJeep18 mentioned. I honestly can't recall the last time I saw a PTC thermistor used in an automotive sensor. :huh:

Tyler I think Paul mentioned in the recent diesel video that the EGT sensors were PTC

Tyler I think Paul mentioned in the recent diesel video that the EGT sensors were PTC

Derp. :silly: You're right! Probably tells you how many diesels I work on...

Thanks Jeep and Tyler. I got many more questions- I wrote a response to AndMacFayden and havnt heard back- I'll try to find it and copy/paste here for you guys

Check this out-

2010 Dodge Ram 1500 (5.7) HEMI

A few months back, I was having intermittent starting issues- meaning that sometimes the truck would start right up and other times, I would have to keep the key turned to run/start for anywhere between 15-45 seconds before it would start? I checked the Batt(+) cable going to starter and was getting proper available voltage to the starter. Also verified the Batt terminals/clamps were clean like newborns baby butt. When it would start and Id drive a small distance and turn the truck off, it would not start again, but would if I hooked up jumper cables? I checked Batt volts and was reading around 12.6V. I was getting the "Red Lightning Bolt" on the dash, so I hooked up my scanner (Autel MaxiSys) and got a code P0123 or bad throttle body. I researched this before I even new Scanner Danner existed and everything says to replace the throttle body. I replaced the throttle body (I know) and same thing. Then people say its the WIN (wireless ignition node) which is not wireless because it has a small 12 pin connector on back with just 8 wires. I took off the WIN ignition key box and opened it up- the small contact arms looked good, so I went ahead a got a q-tip with rubbing alcohol to clean what I could just to be on the safe side- still no difference. Out of curiosity one day, I got under the truck and had the wife turn key to run- No power at starter solenoid? I Ohm'd out the Yellow/Grey wire from starter relay- it was good. I also bench tested the relay with a 9V battery- it was fine-(clicking). I have since torn apart the dash and cleaned up any grounds I could find to include engine and chassis grounds. My next step is to check the starter relay sockets in the TIPM to see if they check out. Also, if Im not getting the volts to the starter solenoid, Im thinking it could be the Neutral/Safety switch which Dodge calls the Transmission Range Selector which I have not tested yet. I dont want to assume anything because I did push ups years ago in the military for using that word.

Im somewhat stumped but am convinced it is probably something very simple. I have the complete wiring diagram from Mitchell and also a downloaded "Shop Manual" supposedly the dealerships use. The shop manual stated that after replacing a throttle body, use a scan tool to do a TPS/Throttle Body Re-learn but my Autel scanner does not have this function.



Update: I started checking continuity and their is an OL between MAP Sensor 5V Ref and PCM (weather has been bad and I have not looked for the break yet)

I need some guidance on this please. Any info/recommendations you could give would be greatly appreciated.

Thank You Sir, in advance-
MrMike

Three types of temperature sensors NTC, PTC and Thermocouples.
NTC are by far the most common in automotive applications, they generally at a cold start have thousands of Ohms resistance which falls to few hundred ohms as the engine warms up. Generally not suited to very high temperature applications. You have to take care with these sensors to fit exactly the right part as the resistance is tailored to the instrumentation.

PTC are much less common but suited to more high temperature applications.

Thermocouples don't work on resistance when heated they actually generate a voltage, not often used in vehicles you will find them measuring high temperatures in jet engine exhausts, domestic heating boilers, furnaces and ovens.

With modern vehicles the signal from the NTC coolant sensor no longer goes directly to the gauge it is read by the ECM then shared to the instument cluster and heater module. The actual gauge on the dash shows only what the modules want to show the driver. For example the needle may move to mid position "N" at 65C and remain planted on N until 110c is reached and only then suddenly move higher.
As 110c is well above boiling point of plain water at atmospheric pressure if the system is not 100% pressure tight this can result in the coolant boiling but the temperature gauge still on "N".

www.delphiautoparts.com/gbr/en/resource-...s-temperature-sensor

This table shows the resistance of a fairly typical automotive NTC sensors in this case from the Inlet Air Temperature Sensor Bosch CRD1 injection system on a BMW diesel.



This what the dash gauge on a BMW or Rover shows as coolant temperature ---- the computer only gives highly processed information to the driver the temperature gauge is not a true indication of engined temperature.

Thanks Andy-

This definately clarifies alot also adding the charts helps too. I greatly appreciate it. When you have time, could you read my post here about the issues with my Dodge Ram. So far, I started from scratch and disconnected all the sensors and did a continuity check on about half of them and found an open or OL from my MAP 5V Ref to the PCM connecter. The weather has been snow here and I have not been able to get out and take the wire loom and tape off to actually find the issue with the MAP wire. When I do, Ill let you know what I find. Other than that, all is good here in Wild and Wonderful West Virginia. Any suggestions you may have, would be great. Have a great Sunday. (Where in England are you at?)

Thanks,
MrMike