95 Disco OBD code 14, thermistor fault....

[skrufy]

Hi-

can anybody tell me which sensor on a '95 3.9l engine gives you a OBD 14 code- "coolant thermistor" to the ECM?

I'm out on the road, and don't have my manuals with me- the Electrics Manual gives great info once you figure out how to read it in Brit Disco Speak/Symbols, and has pictures/locations of all connectors, switches, etc in the back of it...

It should be one of two electrical sensors mounted vertically on top of the intake manifold just to the rear of the thermosat and almost under the coolant hose from the radiator- which can be moved enough to get at either sensor......

One sensor/switch tightens up with a 19mm wrench, and has a 2 lead wire connector on top that you have to move the locking/retaining clip to remove the connector from the sensor/switch. Except the locking clip on the connector on mine is broken, and allows the connector to jiggle on the switch, and therefore possibly sending a fault code- 14. Or could this sensor/switch be good and not have anything to do with the ECM/OBD fault system- just a loose connector....... or

Could it be the other sensor, a single wire push on plug type connector that is smaller, only about as wide as a ball point pen, and probably tightenens up with a 13mm wrench- is that the "coolant thermistor" that would send a Code 14 to the ECM??

As I understand it, the faulting sensor sends a "I'm cold" signal to the ECM, which gives way too much fuel on engine start, flooding etc.

Any help is appreciated! my Disco isn't running worth a damn and have to buy the proper replacement- I'm sure LR would be willing to sell all the possible sensors- everywhere, just to makesure all the bases are covered.....

thanks,
Tim

 

[byronAU]

Simple!.....[on a Disco 1] it's the sensor NEXT TO the thermostat housing that signals to the ECU ......the sensor that screws into the actual thermostat housing is the sensor for the temp guage in dash!

 

[skrufy]

HI-

Thanks for the reply.....

-there are still the two sensors in question- both mounted vertically and not in the the thermostat housing. The sensor in the thermostst housing (now we're talking about a 3rd sensor...) is mounted in the front of the housing, and parallel to the ground or axis of the engine- this lead then goes to the guage on the instrument panel it seems...

A correction to my first post- the smaller sensor has 2 wires to it as well, but is a push on connector like a spark plug wire- it is about 1 inch away from the larger plug/sensor described above.... both are nearly under the large black rubber coolant hose, with the smaller sensor almost under the fuel rail to the fuel injectors.......

It's this smaller sensor that I suspect is the Code 14 fault giver- is about $23 vs about $40 for the other 19mm one..... any more clarifications from Down Under or anyplace else would be greatly appreciated!

thanks-
Tim

 

[byronAU]

HI-

Thanks for the reply.....

-there are still the two sensors in question- both mounted vertically and not in the the thermostat housing. The sensor in the thermostst housing (now we're talking about a 3rd sensor...) is mounted in the front of the housing, and parallel to the ground or axis of the engine- this lead then goes to the guage on the instrument panel it seems...

A correction to my first post- the smaller sensor has 2 wires to it as well, but is a push on connector like a spark plug wire- it is about 1 inch away from the larger plug/sensor described above.... both are nearly under the large black rubber coolant hose, with the smaller sensor almost under the fuel rail to the fuel injectors.......

It's this smaller sensor that I suspect is the Code 14 fault giver- is about $23 vs about $40 for the other 19mm one..... any more clarifications from Down Under or anyplace else would be greatly appreciated!

thanks-
Tim

The ONLY other thermistor in the whole of that EFI is the Fuel Temperature Sensor.....

 

[skrufy]

Hi Byron-

thank you very much for your replies-

I am familiar with and have replaced the Fuel temperature sensor that was causing a cold start problem previously posted by me- I live at 8100 feet, and experience some pretty cold temperatures in the winter- the cold start/temperature modifications have been discussed here- including replacing the prom in the ECM with the updated one, which I did when it was about 10f outside- the prom mod is standard in Canada I guess, but not in the USA.....

I do not have my LR Electrics Manual with me, so I don't have the circuit diagrams to trace and follow which sensor does what and figure this out myself..... most of the test values- resistance in ohms at various temperatures for whichever electrical component, etc. is available only at the LR dealer with Test Book, or is available through subscription repair programs to various independant service shops for all the cars they might service- all for an annual big $$$ fee for updates- I have access to that as well- at home- but not in my current location.....

If you have the Dicso Electrics Manual, circuit diagrams, or whatever, all I need to know is which of the two electrical sensors/switches/devices described above in my
earlier postings sends the Code 14 signal to the ECM- I will then replace that component and be one my way...... both the 3.9l and 4.0l engines, USA specs, have these electricas devices in the described locations..

Thanks again to all that have reviewed these posts, and to you Byron, for so willingly and graciously sharing info on these vehicles that we all seem to care so much about-

Tim

 

[byronAU]

I'm pretty sure then, that the "Coolant thermistor" referred to in the fault code must be the coolant temp sensor that sends to the EFI ECU.....and having re-read your original post and the symptoms described I can confirm that it is the one at fault.......mine had a loose/dirty connection and caused excessively rich mixture that sooted up the spark plugs......My indy LR specialist just cleaned the connector with electronics contact cleaner and re-connected it using silicon grease.........I've just checked my LR Factory Work Manual and that sensor is fed, along with the fuel temp sensor and throttle position potentiometer [all 3 in parrallel], with power from the MAF .....I remember my mechanic told me that a bad connection causes it to go to default which is the rich setting, so it will start and sort of run....according to him a bad connection shows no fault codes [like mine, it showed up NO FAULTS] so I could/may deduce that yours is indeed faulty.......I hope this helps!.......try connecting it firmly or if it still runs too rich/sends the same fault code it must be no-good....I can't really think of much more ATM, sorry.

 

[skrufy]

Good Morning Byron-

Never been to Sydney or Down Under- friends have said it's beautiful-

Your mechanic friend is correct- a faulty sensor- (or connection if the sensor is actually still good...) in this case, the coolant temp thermistor- defaults to a full cold indication as it normally would after the vechicle sits all night for instance- at start up, it gives this cold signal to the ECM which gives extra gas for initial ignition and until it senses the engine has warmed up to some preset temperature.....

THe fuel temp sensor does the same thing- it also will cause a too rich indication from the ECU- all causing rough running conditions from your LR....... both types of temp sensors or thermistors work of off resistance- in ohms- and is pretty simple to test with a multi-meter and a thermometer- (in this case my wife's digital cooking one- she still doesn't know........). In testing the fuel one- I assumed that the fuel temp was somewhat close to the coolant temp- with the thermometer stuck in the coolant reservoir. You then just place your ohm meter on the sensor leads, and measure the resistance change as the coolant heats up. You have to have the resistance values for the sensor in question from either the LR Test Book, or from one of the other programs from a friend in your local repair shop as mentioned above.

I have the ohm values for the fuel temp sensor at home if anyone needs it- will gladly forward it on to you........

I do not have, and need the values for the coolant sensor, and I need to know which of the two sensors memtioned above is the actual coolant thermistor so I can replace it- I think my connection is good, but one of the sensors is bad- but which one???

As an aside- I was flying a Lear35 a few years back and had an engine roll back on final approach into Dallas Love Field- with 5-6 hours to spare, we flew it up to Wichita,
Kansas to the Lear Factory to get it fixed- probably 3 hours later, after a new $25,000
engine fuel controller, plus parts, labor, etc. and an engine run- we headed back to Dallas- only to have the engine roll back again on final..... big $$$ for the wrong fix...

thanks for all the help!

Tim

 

[skrufy]

Hi-

A follow up and conclusion to this thread....

The thermistor sensor that sends the fault Code 14 OBD to the ECM is the larger two prong unit- the one removed with a deepset 19mm socket- as described earlier in this thread..... the smaller sensor goes to the dash gage to the best of my knowledge and uses a 13mm socket for removal...

Once the new sensor was installed, I was able to clear the Code 14 after one attempt (see the TECH section for clearing OBD fault codes for all that aren't familiar with this procedure.....), and then cleared the amber Check Engine light by disconnecting the neg lead on the battery for about 30 seconds- (don't forget to have your security code handy to reset your radio after you reconnect the battery.....)

Problem solved- again, thanks to all for reading/helping/responding to this post!

Tim