Mazda 3 check engine light

[Byteme]

The check engine light came on in the Mazda 3, 2006 with 92K miles.     Autozone read the code and said it was:

1. Low coolant, or
2. Bad Theromstat, or
3. Faulty coolant temperature sensor.

I checked and the coolant isn't low so it must be either the t-stat or the sensor.   Anyone have any experience replacing those parts?  I've looked and frankly I'm not sure know what the sensor looks like.  I know it's on the driver's side of the head (2.0 L engine) but there are three things there that look like likely candidates.  Anyone got a picture of the location and any advice on things to worry about when changing it?

If that doesn't work I'll replace the thremostat.   

[giant_mtb]

Does the engine not seem to get up normal running temperature, as per the temperature gauge on the dashboard?  Does the temperature gauge work properly?

[Speed_Racer]

Oddly enough, I think my thermostat just went bad this morning. I overheated on the way to school and had to get it towed to the shop. I replaced it on my previous car and it wasn't difficult.

I don't know the set up of your 3, but on my car, the t-sensor is easy to reach and replace.

[Byteme]

Does the engine not seem to get up normal running temperature, as per the temperature gauge on the dashboard?  Does the temperature gauge work properly?

Further research on Mazda 3 forums tells me it's likely the t-stat stuck in the open position.  It appears to be in a hard to get to place.  The gauge shows engine just shoy of midway between C and H, but who knows how accurate that gauge is.  The feel test, is the air from the vents blowing hot, tells me the car is running cooler than it should.  I'm thinking I need to replacet he T-stat first.  After almost 5 years the coolant is past due for changing anyway.

[Byteme]

Yesterday the light went out on it's own, so I'm doing nothing to the car mechanically unless the light comes on and stays on for a while.  I think I will change the coolant this weekend.  After 57 months and 93,000 miles it's probably due.   

[VTEC_Inside]

My guess is that it was P0128 - "Coolant temperature is below the thermostat regulating temperature".

Checking the coolant level is easy. Checking the sensor is easier with a scan tool that can show you live data, but can be done the old fashion way with a multimeter as well. You just need to probe it for resistance and watch it change as the engine heats up.

In all likely hood though, its the T-stat that's gone bad. I've already seen this on at least 3 newer (<5-6yr old) cars. I guess they are just using cheaper material for the springs and they wear out faster to the point where they open too easily. Not a big problem until it gets a bit colder outside and codes start flying.

[Byteme]

My guess is that it was P0128 - "Coolant temperature is below the thermostat regulating temperature".

Checking the coolant level is easy. Checking the sensor is easier with a scan tool that can show you live data, but can be done the old fashion way with a multimeter as well. You just need to probe it for resistance and watch it change as the engine heats up.

In all likely hood though, its the T-stat that's gone bad. I've already seen this on at least 3 newer (<5-6yr old) cars. I guess they are just using cheaper material for the springs and they wear out faster to the point where they open too easily. Not a big problem until it gets a bit colder outside and codes start flying.

You are exactly right.  Strangely though, the light went off when it got cooler outside (32 degrees this morning).  I'll just monitor it and change the t-stat if the light decides to stay on.   

[VTEC_Inside]

You are exactly right.  Strangely though, the light went off when it got cooler outside (32 degrees this morning).  I'll just monitor it and change the t-stat if the light decides to stay on.   

One of the cars I saw it on was my buddies parents Grand Am. It did something similar there where it would go on, then disappear. I guess there is a time threshold that it allows before it triggers so depending on how you are driving you could also never set it off.

[Byteme]

One of the cars I saw it on was my buddies parents Grand Am. It did something similar there where it would go on, then disappear. I guess there is a time threshold that it allows before it triggers so depending on how you are driving you could also never set it off.

27 mile commute, one way.   that should set it off

[VTEC_Inside]

27 mile commute, one way.   that should set it off

Not necessarily. If you are constantly driving you'll heat it up good and proper. If you are sitting still a lot, it'll cool down which can cause it.

[sparkplug]

Hope thermostat is stuck open. Sensors cost a fortune. I mean $$$$$$$$$$$$. You'll want to fix it because an engine get better fuel economy at optimum engine temperature. Plus the heater gets the heat from the antifreeze that's heated by the engine. Plus the winter temperatures means your engine coolant is going take longer to heat to optimum levels.

[Byteme]

Hope thermostat is stuck open. Sensors cost a fortune. I mean $$$$$$$$$$$$. You'll want to fix it because an engine get better fuel economy at optimum engine temperature. Plus the heater gets the heat from the antifreeze that's heated by the engine. Plus the winter temperatures means your engine coolant is going take longer to heat to optimum levels.

The T-stat is about $50 as is the sensor.  The stat is stuck open, if it's stuck at all.  I still start to feel heat started after I drive about 100 yards (same as always) mileage according to the trip computer is slightly less than 2 months ago, but I attribute that to the switch to winter blend fuel. 

[S204STi]

VTEC nailed the diag as usual. . I'd say ignore it unless it becomes a chronic problem. Maybe see what the coolant change interval is and just replace the t-stat at that time.

[r0tor]

Ok simple diagnosis....

If you drive around for 15 minutes in coldish weather and you heat never gets hot - you got a stuck thermostat.  If your heat gets roasty toasty but your engine temp says its low, then you got yourself a bad sensor

[Mustangfan2003]

The T-stat is about $50 as is the sensor.  The stat is stuck open, if it's stuck at all.  I still start to feel heat started after I drive about 100 yards (same as always) mileage according to the trip computer is slightly less than 2 months ago, but I attribute that to the switch to winter blend fuel. 

$50 really?  Most I've seen are less than $10

[The Pirate]

$50 really?  Most I've seen are less than $10

Parts for Mazdas are stupid expensive.  I love my car, but I cringe every time I have to replace something (which thankfully isn't often).  Mazda cars don't sell in the volume that Impalas, Accords, etc. sell, so I'm guessing it's an economies of scale thing, but it's ridiculous.  I paid $380 for a brake caliper once, because the Mazda dealer was the only place that had it in stock and I needed it that day.  For reference, remanufactured from NAPA was something like $170, which is still kinda pricey for an economy car.

[Mustangfan2003]

Well just did a quick search and I can see why it could be $50, the whole housing comes with it. 

[Byteme]

Well just did a quick search and I can see why it could be $50, the whole housing comes with it. 

That's good and bad.  Easy to install since it's in a tough to get to location but costs more. 

[Byteme]

I replaced the thermostat yesterday even though the check engine light had again gone out on it's own.  We'll see if it stays off.  The heater dows seem to blow a bit hotter so hopefully that was the problem.  The toughest part of the job was the removal and replacement of those whore-like hose clamps.  They are in a position where it's difficult to get a grip on the ears to remove them.

[Secret Chimp]

Parts for Mazdas are stupid expensive.  I love my car, but I cringe every time I have to replace something (which thankfully isn't often).  Mazda cars don't sell in the volume that Impalas, Accords, etc. sell, so I'm guessing it's an economies of scale thing, but it's ridiculous.  I paid $380 for a brake caliper once, because the Mazda dealer was the only place that had it in stock and I needed it that day.  For reference, remanufactured from NAPA was something like $170, which is still kinda pricey for an economy car.

Not for Miatas. Sharing many or all components for almost a decade, depending on what you're talking about, is pretty handy.