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[Fixed!] 1998 Nissan Frontier with KA24DE -- Temp Gauge

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3 years 10 months ago - 3 years 8 months ago #39968 by JimT
Hi folks, new here, and have been very impressed with Danner's videos. I have the Nissan above and the temperature gauge in the dash intermittently pegs to hot. I don't believe the truck is actually overheating because the needle will suddenly revert to normal and I have used an infra-red thermometer to shoot the radiator hose and the temperature is not too high. The temp sensor looks to be a one wire sensor and the sensor seems to decrease in resistance the higher the temperature gets.

Can anyone guide me on how to test the sensor to see whether it's the sensor, the wire, or the gauge? I'd love to make this thing work correctly. The check engine light is also on, but I'd like to tackle the seemingly simpler problem first so I start with a win. Thanks,

Jim
Last edit: 3 years 8 months ago by JimT. Reason: It's solved! (Added Fixed to Title)

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3 years 10 months ago #39989 by tech25
I would replace the sensor, its cheap, and will give you a starting point from there on. make sure the cooling system has no air in it, and is in good working order.
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3 years 10 months ago #40012 by JimT
I can certainly do that. I'll report back.

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3 years 10 months ago #40022 by tech25
To be clear, you are going to replace the temperature sending sensor, also known as a thermal transmitter. not to be confused with the engine coolant temperature sensor that the engine ECU uses. this sensor is located on the right side of the block, behind the throttle body.

you can test it if you want, or do a cluster internal check for gauges. follow the instructions

part # 25080-89907

Attachments:

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3 years 10 months ago #40034 by JimT
Tech25... yes, the thermal transmitter. Regarding the location you mentioned, I thought it was up towards the front of the block and right next to the coolant temperature sensor that the ECU does use. It's next to that and two engine grounds. I'm showing it as F10 on page EL224 in the service manual.

I did the gauge check according the text you pasted and the temperature gauge reacted as depicted that it should in the service manual. The thermal transmitter is on order and it's supposed to be here Monday. I can report back then, Thanks for your help. Failing to understand this is driving me crazy.

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3 years 10 months ago #40070 by JimT
Update: got sensor today. Bad news... wrong sensor. Had to return. Ordering another and will post here when I get it installed.

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3 years 10 months ago #40166 by JimT
Installed new temperature sensor. Test drove. Gauge still randomly pegs to hot. Bummer. Anyone know exactly how this gauge works? When it goes hot, does that mean it could be grounding out to something?

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3 years 10 months ago - 3 years 10 months ago #40171 by Hardtopdr2
Check wiring for chaffing if non then i would suspect guage cluster and wires under dash or air in cooling system that needs bled out. Does your wiring diagram show one of two ect sensors?
Last edit: 3 years 10 months ago by Hardtopdr2. Reason: Adding more to response
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3 years 10 months ago #40172 by John Clark
Man, here we are on ScannerDanner.com and we had advice to throw a part at it?

Why not unplug the connector to the sensor and see what happens on the gauge. Then short the wire to ground and see if there is any gauge change.

Also, that should be a 5v reference that is pulled to ground by the thermistor. This is chapter 6 in Paul's book. Unplugged it should have 5v on it that you can check with a meter or scope and then when plugged in the resistance in the thermistor is varied by the coolant temp. Once plugged in you should be able to backprobe and see what kind of voltage is showing on the wire. If it's somewhere between 0.5 and 4.5v then the sensor is probably good.

You'll also want to get a wiring diagram for the circuit. It's not uncommon to have more than one temp sensor...one for fans or PCM input and another for the gauge. You need to make sure you're on the right sensor.
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3 years 10 months ago #40173 by John Clark
Actually, I have a diagram for a 97 Pathfinder and, assuming it's the same or similar, it shows 12v coming from a fuse, going through the temp gauge, straight to the temp sensor. So, my above theory about a 5v reference on the temp sensor wire would likely be incorrect. The theory is the same, though. Unplugged you should have voltage on the wire to the sensor. You'll need a meter to measure it, not a test light.

In theory, if you unplug it and turn on the key, that would be high resistance, so low temperature should be indicated. If you short the wire to ground, that would be low resistance and high temperature. If the gauge sweeps properly but always reads full hot that tells me to look for either a shorted sensor or a shorted wire. If you unplug it and it still reads full hot then likely a shorted wire between the temp sensor and the gauge.

You can also do the ohm check of the sensor and make sure it matches the specs in the above post.

Also, it looks like the temp sensor that goes to the computer has two wires and the gauge sensor has one wire....again, assuming the 97 Pathfinder is similar.

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3 years 10 months ago #40195 by JimT
Gents, thanks for the help. I would suspect the wiring is very similar to a 1997 Pathfinder. Hardtop, it has two sensors, one for PCM and separate one for the gauge. Unplugged, the gauge reads cold. Grounded, it reads hot. With my multimeter, I'm getting 11 volts at the connector. I jiggled the wire around and tried to get the voltage to vary, but it held steady.

I haven't backprobed yet and I need to get the diagram back out and check the rest of the circuit. I'm not even sure if it's fused or not. Thanks guys! It's starting to make sense.

One more thing... after I changed the sensor and it randomly went hot again, I stopped and put the cluster in diagnostic mode. The gauge responded as it should have, even though in regular mode with the truck running, it was pegged hot. I don't know what that means.

But, since it will just quickly go all the way hot and then "fix itself", that really seems like it's shorting somewhere. I just have to find it.

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3 years 10 months ago #40196 by John Clark
Yes, unplugged it is normal for it to go full cold. Does it stay full cold when unplugged and wiggling the wire? If so, it sounds like the rest of the circuit is working properly.

Did you ohm check the sensor as described in the manual photo above?

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3 years 10 months ago #40197 by JimT
Question for you guys... The next time it goes haywire, if I jump out and pull the connector off the sensor and the gauge still reads full hot, that would indicate a shorted wire, correct?

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3 years 10 months ago #40199 by John Clark
Yes. You could even unplug it and drive it unplugged and see if it jumps to hot.

Someone mentioned this above already, but did you confirm that you don't have any air bubbles in the coolant? The level is full and you have good heat in the cabin? A lot of those have a small air vent plug on the intake manifold you can pull while filling. You then fill it until a steady flow of coolant flows out of the air vent, with no air bubbles, then put the plug back in and tighten it down.

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3 years 10 months ago - 3 years 10 months ago #40201 by JimT
Sorry... missed this post... been hanging with the family. I have not ohmed the sensor yet. I'll get that done, and also do another wire wiggle. I was thinking and my first attempt was not comprehensive enough. I'll report back tomorrow evening. Thanks for everything! Edit: and check for air bubbles!
Last edit: 3 years 10 months ago by JimT. Reason: Forgot something else!

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3 years 10 months ago #40216 by JimT
Not too much to report today. I drove it 25+ miles and couldn't get it to misbehave. It started the sweep to hot one time but didn't even make it to 3/4 before it reversed course and went back to normal. I ohmed the sensor 4 times... cold, it was over 1000 ohms; when gauge first went to normal, 170 ohms; at around 15 miles in, it was 132 ohms; and at the end when I got back home, 126 ohms. That's within spec, so I think the sensor is doing what it should.

I turned KOEO before I started and really tugged on the harness all the way up to where it goes through the firewall and couldn't get the gauge to move.

I didn't check the air bubbles, but I did find the air valve. I'll bleed it first thing tomorrow afternoon when I get home from work and the truck is cold.

I also think next I need to figure out where the Flexible Printed Circuit is that the sensor wire runs to. Anyone know if that is actually in the cluster? Thanks.

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3 years 10 months ago #40217 by Hardtopdr2
It should be in the cluster assembly otherwise it's a circuit board

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3 years 10 months ago #40218 by JimT
Great, thanks.

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3 years 10 months ago #40219 by John Clark
Remember, in order to go full hot the wire needs to short somewhere. Sometimes, however, there is a temperature threshold where these needles will display full hot. You do need rule out the possibility of actual hot temperatures and air bubbles in the coolant or low coolant.

it would be helpful to use a scan tool to watch the coolant temp that is being sent to the PCM during your drives and compare to what the gauge is telling you.

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3 years 10 months ago #40231 by JimT
"You do need to rule out the possibility of actual hot temperature..." Yes... so about that. This afternoon, I opened the radiator cap and the air relief valve. The coolant was all the way to the filler neck and in the overflow bottle it was just over the max line. I started the truck and let it warm. Had steady coolant coming out of the air relief valve. Closed the valve and topped off the radiator (which had gone down when coolant was pouring out of the air relief valve).

I back out of the driveway into the street. At that time, the gauge pegs hot. Great! That's what I need! I pop the hood and jump out and disconnect the gauge. Gauge goes cold when disconnected. Oops. Not what I was expecting. Plug it back in, gauge goes hot. Dang. Pull back in driveway and run to get my meter to ohm the sensor, but then it went back to normal. Crud. But, the evidence suggests that my gauge may actually be functioning. Kind of embarassing.

I like the scan tool idea. I have a friend with a scan tool and I'm going to try it. It's a snapon Modis. We tried it a while back and it said it could not communicate with the truck. But, it will read in generic obd mode. I don't know why that is. I'll see if it can read the sensors in generic mode. Thanks for the idea.

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