Coolant temp sensor nightmare issue

[corey240]

Ok, so iv searched and searched a couple forums and did a couple test to my understanding and helped nothing.the car is a 98' s14 with a redtop sr, front mount, exhaust, walbro fuel pump. heres the problem, the car sat for roughly 8 months with nothing ever messing with the ecu or the wiring to it. i rebuilt my motor, now i put it in and long story short i checked for codes and its 100% the coolant temp sensor , whether its wiring, or a bad ecu, i dont know. but it has all the symptoms of a bad cts, the temp gauge doesnt work, and the ecu is throwing code 13 aka cts problem. so i swapped the sensors with 2 others of each kind and the same thing, i swapped the sensors and reset the ecu with no avail.
I have followed the wiring to the sensor for the ecu and all is good. the wireing for the gauge sensor is also good up to the ecu area where i didnt see the need to follow into the dash because...
Prior to the rebuild back when the motor blew, it ran fine until the rod knock. the gauge worked, i had code 55 (nothing wrong) and all was great (except for the rod knock). so now i am totaly confused on what can be wrong, how could my ecu be bad? is it bad? (i h ave no other sr's to swap ecu's with to test), could the wiring for the ecu sensor have just gone bad and needs replaced? (meaning the wire thats wraped with a ground wire needing replace),.
what should i do to figure this out? i cant find what to turn my multi meter to, to test the wires coming from the sensors, i know what they should be at but i dont know what to set the multi-meter to. im trying to come up with a list of considerations to test and replace. when it comes down to it i think either for some reason the ecu went bad or the wire just went bad somhow and doesnt wnt towork anymore.

[RPS1392]

Verify your engine harness, and block ground points.

[corey240]

as in tell you where they are? or check them? they are all the same as befor. would it be good to add one? i have like 1gauge cable i can use for it. where would i add it to, and if i need to add one to the harness, where to?

[johngriff]

The guage works off the 1 wire coolant temp sensor, and is passive to the ecu's controls.

The two wire sensor is the controlling factor against the ecu.

So, it sounds like a two part issue.
*1 the single wire temp is not connected or snipped.
*2 bad temp sensor?????

Maybe do you have the connector on the harness not connected to the temp sensor pigtail harness?

Do you have a multimeter? Set it to "alarm" and run 1 side into the coolant temp sensor, and the other side into the pickup for the ecu. Does it read a solid 1 and alarm?

Repeat on the 1 wire temp sensor and the temp signal wire to the dash.

[corey240]

see thats the thing. i tore my harness apart to maek shore all the wires are connected (tore apart as in tape/wire loom not cutting wires). so all the wires are connected good and the plugs are ok. i have an s13 with sohc and swapped the sensors with the ones off it and same thing. i bought an s14 ka sensor instead of an s13 dohc sensor like a dumb ass so its useless. but the old sensors worked fine along with the other 2. as in i had 2 extra of each sensor swaped in and same effect.:loco:

[johngriff]

What was the result of the test I requested?

[corey240]

i cant test until tomorow, i have to pull my head and clean it so my hg will stop leaking (comteic). so befor i get into that i want to get a list of things to do to test for the temp sensor bs tonight. il do it tomorow (cars not with me) and post up all results to all tests and things to check.

[corey240]

ok so i went to do that test and found out i have no warning thing on my tester. i have one of thos cheap 20$ black big square multitesters with the knob in the middle. i changed the sensors with 1 other set i found laying around that came off a car that worked fine befor and same thing happend. i did however find that the gauge sensor (small one) will atleast make readings on my tester, but the big sensor will not make the tester do anything at all. sombody please help with this i have this month to fix it or the car is gone.

[steve shadows]

as long as your sure about the wiring, just try replacing the sensors, process of elimintation

[MELLO*SOS]

Since both temp sensors are giving you problems, I venture a guess you have a short in your harness near there.

To use your multimeter, you want to use the resistance 0-200 ohm setting. If you get a very low resistance (drops to .1 or so) then you know you have a good connection. If the resistance bounces all over the place you probably have a short.

Also there is, in the FSM, the specifications for the temp sensor resistance at 70' and at 170'. Look these #s up and test the sensor's resistance using these #s. You'll have to use the 0 to 20k scale on the multimeter IIRC...

You can try unplugging the ECU harness, then testing the continuity (resistance) of the wire going to the coolant temp sensor. Unplug the CTS then use a jumper wire to short the CTS connector plug to ground. Now from the ECU side of the harness, test the resistance of the CTS wire to ground. This will tell you if you have a short in your CTS wiring somewhere...

GL

[johngriff]

iirc, a simple voltage test on the back through the two wire sensor should work.

5 volts constant on one side, and 5 volts and less for the hotter the engine gets. Are you getting 5v on the harness connector?

yeah, duh check the continuity.

[corey240]

well i tested the old wire. the multimeter didnt do anything at all. so i took out the white wire thats wrapped with the chrome ground wire and replaced it and the multimeter reads numbers like its working now so i just gota wait till tomorow to mess with it some more. anything els i should try?

[MELLO*SOS]

.... That's probably it then, it sounds like you found the wire with a short in it and replaced it. Clear the codes, test start the engine and check the codes again. Hopefully no more code 13.

[corey240]

lol, i did that, then what happend was, instead of clearing the codes (unplugging it for a whil) i just turned the car on for a little bit and then checked the codes. i swear it flashed 11 one time then went back to 13. iv left it unplugged overnight though to clear it if thats one way to do it.:duh:

[MELLO*SOS]

That's one way to do it, but the fast/quick way is to just turn the key on, put ecu to mode 2 (twist knob clockwise, hold 2 seconds, twist back). It'll read out any stored codes.. After it's done, put it back to mode 1 (twist knob clockwise, hold 2 seconds, twist back). The light should be on solid & now the codes are erased. No need to unplug from the battery.

It's possible that the sensor itself is bad, read in the FSM about how to measure it with a DMM. Also check the connector plug, mine seems to have some corrosion on it and that's making it have a poor connection.

[corey240]

i took the plug apart an cleaned it, along with another i have thats like brand new. so when you check for codes? it will flash off more then 1 ode if there is anymore then 1? i thought it would only flash 1 code at a time or somthing but either way, if thats how you reset the ecu codes then iv done it about 20 times a day. i left it unpluged last night and its still reading 13. also now, at the ecu (didnt get to test at the sensor) the wire is reading from.03 up to 4.3 up and down, and thats with the new wire there, i swapped the sensor with the others i have and same outcome. i dont think its the sensor because the ones i have are all good specificaly the one thats in there now because its the 1 i used befor the motor blew. im confused on this, i look at the fsm 10 times a day at the same astuff over and over again but i still dont understand wiring diagrams.

id take it to the nissan dealership but 1. i dont want to pay tha tmuch for them to tell me wha ti know already. 2. i know and have cornerd the causes of this and have done up to what i know of to do to fix it and nothing.

EDIT:BTW, when i pulled that wire out (white 1 with chrome wire wrappeda round it with black housing around that) i pulled the black housing off, and carfully unwinded the silver ground wire off the white wire, looking at the white wire i noticed a section was black for like 1 1/2 inch oe lil shorter, when i cut that part of the housing off the wires were fine, wtf was that from? it woulda been inside the car too

[corey240]

this is a direct qoute from frsport website for the 2 wire temp sensor


Product Description


Brand new Nissan OEM ECU temperature sensor (2-wire). If your vehicle is getting bad gas mileage or is having idling issues after the engine has warmed up, your ecu temperature sensor may be bad.
Replacing this sensor will enable your ecu to measure coolant temperature correctly in order to calculate the right amount of fuel for the engine - otherwise it will run rich constantly.


lets hope me getting this wriing trouble figured out will kill 2 birds with 1 stone (my weird idling problem thread)

[MELLO*SOS]

you should be able to measure the resistance of the signal wire (with the sensor unhooked) and have it be really low, like .1 ohm. It should be a solid reading too, not bouncing around (short) Did you replace the entire length of wire or just a short section? Sounds like there's still a short in it somewhere if you're getting the code 13 right away after clearing it out.

[corey240]

yea i totaly replaced the wire from 1 inch from the ecu all the way to about 4 inches from the sensor plug (exact same length as other old wire):bite:

[seven.62]

i hope you figure this out as i am having the same problem

[corey240]

il keep it updated, im testing it right now to see if the right sensor i got fixes it or not.

[corey240]

ok so i went to see if changing the old little sensor would change anything and i wasnt geting any numbers in the wires now for som reason. so i thought maybe there is a weak connection in the plug. so i took the pins out of eeach plug and directly conected the wires to ensure they were connecting properly. i put the test lead on the wire and i smell somthing wierd like a burning smell. so i take 1 set to the driver side to turn the car off and a loud pop goes off like 3 bottle rockets at the same time. i look down and the small temp senor end is missing. the hole thing just exploded off like a bullet. the internals of the sensor exploded out of the thing, wtf is that from. nothing went in the car or anything but im not hooking it up again til this is solved.

[MELLO*SOS]

Huh? It sounds like you ran too much power thru it doing whatever you were doing. Were you giving it 12v off the battery? It's just a little thermistor you overloaded it with too much current and blew it up LOL first time I've heard of that happening...

Btw are you talking about the "old little sensor" meaning the single wire sensor? That thing is for the dash temp gauge, don't worry about it. The red two wire sensor is the one u need to focus on.

Also you mentioned that you replaced up to 4" away from the plug but you still seem to have continuity problems. Have you checked to make sure the last 4" and into the plug are good?

[corey240]

well befor going to court today i replaced the rest of that 4 inches, but i had a warrant and just got bail so i havnt had time to test that bitch. il get back with it tomorow and we will see whats up. but do you mean that the ecu doesnt know anything about the temp gauge? like the wire runs from the sensor to the gauge and since the gauge wont work i could just get an aftermarket one? i was thinking maybe there was somthing wrong with the gauge so the ecu is like hey and the hole time its been the cluster

[corey240]

2 questions.

can the ecu tell that the remp gauge is not working?

and if it cant, could my ecu just be bad all the sudden? i checked the cicuit boards again today closely and it looks good. i tested the blue wire with black stripe on the gauge cluster (swap guide says its for the temp gauge) and it gives me like no reading. could i take a wire straight from the temp sensor and run it straight to the temp gauge and bypass all the connectors it goes through the dash to see if it works? could the ecu tell if the cluster is bad?

[rotation3x]

Did anyone ever figure this out? I have a s14 with a sr redtop swap also. I bought this car with it in there and it was a horrible swap, however the wire harness was done by yuri at wiring specialtys, so I know that is good. Here is my problem my car after sitting 2 days very cold never started I just turn the key to the "ON" position so the gauges come on well the temp gauge already reads like 1/4 way up. When I start the car it idles low like 400-600rpm... tap the gas to keep it running it jumps up to 1500-1700 rpm fluxuating. The guage sensor is brand new the 2 wire sensor I have not checked out.

I had my old car a s14 with a sr blacktop and I swapped the sensor from my Ka and the gauge worked perfect.

Does the temp sensor throw off the ecu to make the engine run higher rpm?

[Slow Poke]

Does the temp sensor throw off the ecu to make the engine run higher rpm?

NO, not exactly. If it's cold the ECU will compensate and run the engine at a higher RPM (VIA: IACV) until warm. If it's jumping up and down then you have one of two problems.
1)Vacuum Leak
2)IACV Problem

And the reason your cluster reading was off is because the ECTS for the cluster is different for the S13/S14. S14 Cluster needs an S14 ECTS (the one wire sensor for the cluster, NOT the 2 wire)

[hingamatt]

I don't gave a FSM, does anyone know the resistance of the one CTS? I goolged it and this post came up. I am wondering if I can use the stock temp sender for an autometer gauge.