Coolant Temperature Sensor

[redline racer510]

I have been having this problem with my 95 240sx for about a month now and i cant seem to figure out what it is. My car is throwing two engine coolant temperature sensor codes and a knock sensor code. The fsm states that the codes are related to the ECT and or the circuit. After testing the voltage in the power wire going to the ect i got 4.89 volts which is pretty close to the recommended 5V required. I checked the ground and also continuity going from the ect to the ecu and the tcu(transmission control unit). The weird thing is that if i reset the ecu the problem and check engine engine light go away for about 20-30 miles then as the car progressively gets warmer the car starts to hesitate and sputter and act like it is going to stall. I dont know what else to do and this problem is really sucking the time energy and money out of me trying to figure it out. For gods sake I am popping out gray hairs trying to figure out what the problem is, please help me. :bash::bash::bash::bash::bash::bash::bash::(:(:(

[g6civcx]

Questions for your question:

1) What are the codes? What numbers?

2) Where did you put your probes to get 4.89V?

3) How hot was the coolant when you got 4.89V?

4) How did you check for ECT continuity to the ECU and A/T control unit? Signal wire goes to the ECU only. The ground is tied to common sensor ground used by the ECU and the A/T Control Unit.

BTW TCU = Time Control Unit.

[projectRDM]

Replace it anyway, it's clear that you're getting a code and erratic signal if the cars acts up when warm. It's cheap and simple to replace.

[s13pignose]

Yeah I probably would, good maintenance and like said easy to replace. Never could hurt, and just one less thing to worry about down the road

[redline racer510]

Questions for your question:

1) What are the codes? What numbers?
13,34,98
2) Where did you put your probes to get 4.89V?
One on a chassis ground and the other at the power wire going to the ECT
3) How hot was the coolant when you got 4.89V?
The car hasn't been on for a couple of days

4) How did you check for ECT continuity to the ECU and A/T control unit? Signal wire goes to the ECU only. The ground is tied to common sensor ground used by the ECU and the A/T Control Unit.
One probe at the ground wire of the ect harness and the other at pin 50 of the ecu. One probe at the ground side of the ect harness and the other at pin 35 of the A/t control unit.

BTW TCU = Time Control Unit.
Thank you for correcting me.

[redline racer510]

I replaced the sensor with a new one but it still acts the same.
I checked the old ect's resistance at the different temperatures specified in the fsm, and all resistance was in recommended working parameters. so there is nothing wrong with the sensor. I cleaned it up and re installed it, i even changed the thermostat and flushed the coolant and properly bled the entire cooling system and it still gives me a hard time. After driving it for the 20-30 miles like i said it doesnt want to start when i turn the car off and when i checked the sparkplugs they were covered in fuel and the cylinders get flooded with gas. My friend said it might be the upstream O2 sensor but i dought that since there is no code for it.

[g6civcx]

13/98 are for the ECT and 34 is the knock sensor.

First thing you should so is check all of your engine grounds. Is the block grounded to the chassis in some way? Did you do a cleanup and remove all the stock engine grounds?

4.89V is just the voltage that the ECU is sending. You know you have proper ECU voltage.

Measure two pins on the ECT subharness. You should get continuity and variable resistance like you said.

Other than that, check the engine harness and see if you have a short on the Blue/Orange and Black wires.

[redline racer510]

There is continuity to the ecu from both wires going to the ect, so the circuit is fine. The more important question is what can be throwing 2 ect codes and a knock sensor code? This problem mystifies the hell out of me, the more i read the more hopeless i feel. I read of a similar problem where 5 , count them 5 nissan techs of varying experience tried to figure a problem similar to mine out and they all pretty much gave up and recommended an sr20det swap,lol. After that the owner of the car handed over to some master nissan tech guru/prophet(lol) and even he couldnt figure out what the problem. I took my car to two techs and they wanted to take nearlly 1000 dollars from me and i also took it to my friends smog shop and put it on the dyno after i reset my ecu and ran it on the dyno for like 15 minutes and the afr's looked normal. So after having these different experiences i am even more interested in figuring this problem out and so does my smog tech since hois cousin has nearly the same problem.

[g6civcx]

There is continuity to the ecu from both wires going to the ect, so the circuit is fine.

You can't assume that the circuit is fine. Having continuity is good, but you need to hand-check the entire length of the wires for short to ground.