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Coolant temperature sensor location

Tiny
G_GONYE
  • MEMBER
  • 2000 NISSAN ALTIMA
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 112,000 MILES
I had an alternator failure and replacement. Have had bad MPG and rough idle since. Noticed that coolant temperature gauge (CTG) drops with power request (accel, hill, even increased RPM at rest in neutral). It seems to be an analog response in that more power equals more gauge drop, down to essentially "cold" reading if merging or overtaking on highway. Also had appearance of an intermittent lose of ALL instrument/dash lights (including radio!), Only the lights go, radio, fans, gauges etc. Still work, just in the dark. Hasn't happened recently.
Diags: Alternator (new) puts out 14V to positive term. Of battery and to ground. This does not change (not even a wiggle) when CTG is actively dropping due to high RPM in neutral. No fuses blown.

Path forward:
1. New alternator and its install are source
2. Failure of old alternator did damage and is the source

Trying to replace coolant temp sensor (bad MPG due to wrong input to ECM) and coolant temp sending unit (weird gauge behavior). Anyone got pictures of where these are? Is this worth doing? Is the voltage regulator a possible suspect? (Does the Gen2 Altima even have a voltage regulator, I can't find it!)
Multimeter tests to clarify?

Thanks!

GG
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Monday, February 22nd, 2010 AT 11:38 AM

11 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Hi g_gonye,

Engine Coolant Temperature sensor is located at left side of engine , near fuel injector # 1.


https://www.2carpros.com/forum/automotive_pictures/192750_ECT00AltimaFig06_2.jpg



The gauge problem is more likely to be a fault with the meter cluster . There have been other reported cases of such.

The voltage regulator is inside the alternator assy.
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Monday, February 22nd, 2010 AT 2:09 PM
Tiny
G_GONYE
  • MEMBER
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Thanks KH. The picture is very helpful. How do I narrow down the problem? How would only one gauge have a problem and how would that affect MPG, idle and performance (also crappy since alternator failure). I need specific teests I can do besides buying and replacing.

Got a picture of the coolant temperature sending unit?
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Monday, February 22nd, 2010 AT 3:12 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Sorry I am not able to find any reference to the temperature sending unit location. It is a 1 wire sensor that is loated near the upper hose where it is connected to the cylinder.

The gauge would not affect the mpg or erratic idle and performance but the ECT would.

For the ECT you can test the temperature and resistance range but requires the use of appropriate diagnostic equipments.

I would not recommend replacing without understanding if it is the cause.

The gauge not showing correctly could be the sending unit wire losing its insulation somewhere and is being shorted to the engine when acceleration causes it to move.
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Monday, February 22nd, 2010 AT 3:50 PM
Tiny
G_GONYE
  • MEMBER
  • 3 POSTS
Thanks again!
Unfortunately it would be best if I could show you the deal in real time. This is purely analog and electronic and, given the crap performance, it is probably sending bad info to the ECM which retards/advances timing inappropriately. It is smooth and instantaneous and identical every time, and the more power you ask for the lower the gauge gets. Sit still or coast rises immediately up to normal warm temp position. I think the gauge and sending unit are fine but getting decreasing (increasing?) Current as the load increases with power request. Even though the alternator appears to putting out a constant 14V to the battery. Something in between the two maybe? What/where/how would I test to find a voltage/amps that are dropping with RPMs and changing sending unit (and probably sensor) output?

Don't bring anymore of that weak jiggly wire stuff! :-)
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Monday, February 22nd, 2010 AT 4:13 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
As the charging voltage is constant, any drop in voltage to the sensors would be from the ECM.

The two items most likely to cause the fault of the ECM providing lower than expected voltages would be the Throttle Position Sensor (TPS) and Mass Air Flow (MAF) Sensor.

Have you ever tried to retrieve for trouble codes or gotten the vehicle on a diagnostic machine to check the various components funtions while the engine is running? Freeze frame data would help in detecting the fault.
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Tuesday, February 23rd, 2010 AT 11:23 AM
Tiny
ROLF120
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I had the same problem with my 2000 nissan altima (and found only this thread with a similar problem). I have had the problem for about 10 months, then finally found a loose connection in one of the coolant temperature sensors. I got that connection fixed (with a hammer and flat head screwdriver) and the problem went away.

I am not a car guy, but could get a picture if you are still having this problem.
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Monday, November 1st, 2010 AT 5:10 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Hi rolf120,

Thank you for the input.

Though symptoms can be similar but causes could be different and any additinal informatin is good for others who might have similar problems.

G_gonye did not come back so either he has solved the problem or has given up on it.

Have a nice day.
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Monday, November 1st, 2010 AT 6:40 PM
Tiny
ALYNNSI333
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  • 1 POST
I am having this exact same issue and I feel like it's an issue somewhere in the circuitry. I just don't know where to start. I'm new to mechanics.
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Tuesday, April 30th, 2019 AT 2:10 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,616 POSTS
Hello,

It sounds like the coolant sensor is going out we should start that first here is a guide to walk you through the repair and use the diagrams above for the location.

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Please run down this guide and report back.
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Thursday, May 2nd, 2019 AT 2:54 PM
Tiny
BASELINER10S
  • MEMBER
  • 1 POST
  • 1998 NISSAN ALTIMA
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 185,000 MILES
The temperature gauge drops to cold when I press the gas pedal. At idle speed, the gauge remains steady in the normal range. But when I rev the engine the needle drops to cold. I get normal heat once the engine is warmed up and both top and bottom hoses on the radiator are warm to hot. I replaced the thermostat but it has not affected the problem.
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Thursday, September 5th, 2019 AT 5:26 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Inspect and test the engine coolant temperature sensor/loose connection here is a guide to help walk you through the coolant sensor replacement with diagrams below to show you where the sensor is on your car.

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.
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Thursday, September 5th, 2019 AT 5:26 PM (Merged)

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