Car Repair: Code P0128 for 2003 Nissan Maxima Changing the Engine Coolant Temperature Sensor (ECTS)


***I am not a mechanic, consult an experienced mechanic for auto repairs.  This is just informational***

What does a blog about personal finance have to do with car maintenance?  Well, it’s my site and I can do what I want.  Also, cars are expensive to own and learning to do some maintenance items on them can save you big bucks at the shop.

My check engine light recently came on in my 2003 Nissan Maxima.  Yes, this is my newer of 2 cars and I would like to keep it for about 3 more years.  The car currently has just over 115,000 miles.  I do not have an OBD-II reader, so I went to the local O’Reillys (AutoZone also does it for free).  They can give you the code that is being triggered on your system and pull up the most likely causes of the problem.  I rarely buy parts from these places, unless it’s an emergency.  The prices are normally about double what you can get online.  My preferred place to get parts is  Even though you have to pay for shipping, the parts are a lot cheaper and you can get a better selection of brands and the total cost comes out a lot cheaper.  From my experience, the cost are roughly about half of the brick and mortar.  So, if you’re not in an urgent situation or have a second car, it can save big bucks.  To turn this into a personal finance article, check out the historical stock price of AZO and then you can figure out why the stock has had a crazy run through the years with the prices they charge.

Repair time took me about 35 minutes with taking pictures and trying different wrenches and sockets to get to the part. But really the hardest part was removing the connection from the wiring harness, because they don’t leave much space.  You can get it done in about 10 minutes with the info below.

2003 Nissan Maxima Code P0128

Code P0128 is an error code related to the cooling system.  The possible problems from my print out are either the thermostat has gone faulty and is either stuck closed or open.  This can lead to the engine either over heating if stuck closed, or not warming up enough if stuck in the open position.  Another possible problem is the Engine Coolant Temperature Sensor has gone faulty.  The engine coolant temperature sensor  (or ECTS or CTS) is used to detect the engine coolant temperature.  Information on the ECTS can be found in the FSM (factory service manual) in section EC-207 and EC-219.  It has procedures for check the part, but since it’s a cheap part to replace and the car is nearing 17 years old, I figured I would replace this first and see if it fixes my check engine light.  I’ve had other sensors needing to be replaced in the last few months, so I figure it’s worth a shot to get the cheaper and easier repair done first, before moving on to the next possibility.  Also, with that age, crud starts to build up on these sensors anyways.  The second possible repair involves the removal of the thermostat, which has a stupid design in this car.  The thermostat is integrated in the water outlet and has 3 bolts, one of those bolts is in a very poorly designed location.

Tools I Used for the Repair

Pretty straight forward.  I used a socket wrench with extension, swivel and a 19mm deep socket.  The deeper the socket the better.  Hex drive, Phillips and Flat Heat Screw Driver, and of course a new ECTS (pic of part below).  I fiddled around and tried out offset wrenches and box wrenches.  Don’t waste your time, you won’t have enough space, so a socket wrench is needed.

The Engine Coolant Temperature Sensor:

Replacing the ECTS on a 2003 Nissan Maxima

I should say that quite a few Nissans sporting the 3.5 Liter V6 or their VQ line of engine share pretty much the same layout, so this repair may be related to other Nissan cars.  Check your FSM.

The first pic is just your standard view of the engine bay when you pop the hood.  First step is to remove the plastic engine cover by removing the 4 hex bolts holding the cover down.  The circle shows what we are trying to get to, the ECTS.  Of course there is stuff in the way, because engineers don’t design cars to be super easily repairable like back in the day of my 83 Datsun 280ZX.

Here is another view of the ECTS, using my laser pointer to highlight the part and circled in red:

and one more view from above:

For the next step, we have to remove the wiring harness connector from the ECTS, it is that black connection.  This took me a little trial and error to figure out.  The space is limited and if you have skinny hands and long fingers you may be able to work it out easy.  Basically, there is a little spot on the connection that you have to press in.  You will hear and audible click.  This will allow you to then gently wiggle the connection up off the ECTS.  What I ended up having to do was remove a plastic box that has an air intake at the front of the engine.  it is held down by 2 plastic screws.  The box ultimately connects to the air filter housing.  This gave me more space to the ECTS.  I also had to use the flathead screw driver to press the release in for the wiring harness  connection.  This made removing the wire connection way easier for me.  This will save you a bunch of time, as I tried several things to try to get access to the ECTS.

Here is a view of what I am talking about removing, highlighted by the red arrow pointing towards the empty space, and also a really good view of the ECTS and wiring connection:

Next step is to remove the wiring harness.  Here is a view of the wiring harness.  The yellow arrow highlights the little pin that you have to press in until you hear the click.  The flathead screw driver held me to get enough pressure.  You should be able to click on the image and see a really big pic for better reference:

Once you have the connection removed, you can just tuck it off to the side.  There should now be good enough access to the ECTS from above to remove it using your socket wrench, extension, swivel and 19mm deep socket.  You will notice that you do not have a clear shot at the ECTS, a rubber hose will sort of be in the way, so the swivel really helps out here.  Walmart has the swivels for the cheapest price.  The part has been on the car for 17 years, so it will take a little pressure to get it to budge.

Here is a blurry pic comparing the old (top in blue) and new (bottom with black connection) ECTS.  Trust me when I saw them, there was a little corrosion on the old ECTS from 17 year of sitting in anti-freeze.  Notice the keys to my old Z above, it’s a freakin beautiful car.

Installation is the reverse steps from above.  On my new ECTS, I used a little anti-seize compound on the threads.  I like doing this to anything that screws into parts of the engine that are exposed to high heat.  Without anti-seize, threads can become fused to the metal components they are attached to on the engine.  The most common application is on spark plug threads.  I have a little tube from Permatex and it’s pretty much a lifetime supply for me.  It’s pretty cheap insurance and makes future removal pretty easy.  Also, you should thread on the new ECTS by hand first, to avoid cross threading.  Once you have it snugged down by hand, grab your socket wrench to give it a good final tightening down.  Unfortunately, the FSM does not provide torque specs, so don’t go to crazy.

Once you have the ECTS installed, connect the wiring harness (you will hear a click when it locks in), install that plastic airbox back to the air filter housing, and reinstall the plastic engine cover.  You should start the car and check for any anti-freeze leaking from the ECTS.  From here, driving and putting on a little mileage should get rid of the check engine light, indicating the problem is fixed.  If the check engine light does not go away, you still have a repair to do.

Overall, this repair cost me $10 bucks and took me about 30 minutes to do.  With some of the tips above, you can probably get it done in about 10 minutes.  Looking online, repair shops charge around $150-$200 for this particular work.  So it turns out this is a personal finance article, you just saved some good money.

And for fun, an overhead view of my ’83 Datsun 280ZX


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