2000 Nissan Altima

Electrical problem
2000 Nissan Altima 4 cyl Front Wheel Drive Automatic 112000 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?


February 22, 2010.

Hi g_gonye,

Thankk you for the donation.

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

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.

Feb 22, 2010.
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?

Feb 22, 2010.
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.

Feb 22, 2010.
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! : -)

Feb 22, 2010.
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.

Feb 23, 2010.
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.

Nov 1, 2010.
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.

Nov 1, 2010.