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2003 Saturn L300 Issue

I have an occasional issue when pressing the gas pedal while stopped or at low speed the car hesitates and slightly kicks. It doesn’t seem to happen at high speeds. The auto mechanic I took it to said he is getting a read that it might be the thermostat. My temperature guage has not moved above normal. The auto guy says they need to start with the thermostat and see where we are with the problem at hand afterward. This does not make sense to me. Maybe the electronic read is right and the thermostat needs replacing, but how can this affect my occasional hesitation problem?

Are you sure he said thermostat and not temperature sensor?

If you feel uncomfortable with his diagnosis, try a different shop.

yes he said thermostat. yes i think another opinion will be good. thanks.

I don’t know about the L300 series, but the S series Saturn’s have a long history with the ECTS (engine coolant temperature sensor) and its connector. The computer is very sensitive to the coolant temperature and will set a code if the thermostat is even 1 degree below set point, so I would rule out the thermostat.

If you replace the ECTS, you must use the GM sensor with the brass sensor end and replace the connector as well, but you really want to be sure this is the problem before doing this. You need a mechanic that knows how to use environmental splices and does use them.

But again, this is an L300 so I don’t know if all that applies. Do you get a code or a check engine light? If so, post the code here, not the mechanics interpretation. You can have a stored code without a check engine light.

BTW, I’m inclined to think the issue is related to a vacuum leak more than anything else, but could also be a bad spark plug or wire.

When ever a mechanic (?) starts off with … we have to start with replacing xxx and then go from there, or words to that affect, you need to say thank you and leave, and not return.

Thank you Keith! Very helpful! I have a check engine light that stays on, but this hesitation problem only happens when the service car light comes on just above the check engine light. I will check with another mechanic and ask if he uses environmental splices.

First things first, get the codes read at AutoZone or Midas and post the code number here, i.e P0200 etc. This the place to start, do not start by throwing parts in it and hope for the best, that gets real expensive, real fast.

These cars were based on an Opel V6 and are very complicated to work on. My mechanic refused to look at my granddaughter’s L300 because the repairs quickly get so expensive that people won’t pay the bill and he gets stuck with the car. Her car needed, among other things, 4 converters at $1000 each. It didn’t get them and when she was done with the car she sold it to someone in a no inspection state. Her problem started as a hesitation when you stepped hard on the gas.

As Keith says above, if the CEL is on, getting the codes read and posted here is the first priority. You purchased the diagnostic software when you bought the car, so you might as well take advantage of it. Just replacing parts could work, but you might run out of money before you fix the problem.

Besides the ideas above, a throttle position switch (or sensor) on the fritz can cause this symptom. As can improper idle speed or idle timing. Good idea to have all three tested I think.

AutoZone printout from their CEL read says OEM Number to Cross: P0128.
Coolant temp is always low
The powertrain control module verifies that the engine is at a proper operating temperature.
Probable cause
1 - Check coolant level (this is good btw)
2 - Thermostat defective
3 - ECT (engine coolant temperature) sensor defective

Could these things be the reason for my hesitation and kick in the low gear and for the Service Car Light to come on above the CEL? I have no diagnostic software. I bought the car used. Maybe this is something I should search for to buy. Oh it’s not sounding good oldtimer 11!

I didn’t look up the P code, but assuming items 1,2,3 corresponds to that p code, hmmm … yes, it could cause that. Especially if the coolant temp sensor was defective or wasn’t plugged in. My Corolla will barely idle at all if I disconnect that particular sensor. The check engine light would almost certainly be on if that sensor is unplugged. Is the CEL on?

And a stuck-open thermostat could cause these symptoms too, and it would be most noticed when the weather turns colder, like now. So that’s certainly a possibility.

The ECT is a fairly simple thing to test usually. It is just a gadget that changes resistance with temperature. Your mechanic could simply unplug its connector and measure the resistance at ambient temperature and wouldn’t even have to remove it from the engine. If it is ok at ambient temperature, it is most likely working, then the mechanic could move on to inspecting/replacing the thermostat. On most cars changing the thermostat is also a “short money” item. It doesn’t cost much for the part, and doesn’t take much time to replace. When I do this I always put the old one and the new one in a pan of water and heat it up on the stove with a thermometer, verify the new one is working and the old one isn’t. Other than the idea of first checking the coolant temp sensor, it looks like your mechanic is on top of this. Best of luck.


Here are 2 common causes for P0128

Stuck open thermostat
Coolant level low . . . below the level of the sensor

I think your mechanic has the right idea

My recommendation is do a coolant drain and refill, and change the thermostat

Mind you, this recommendation is only for P0128, not for the hesitating. That may be something else.

Basically the P0128 gets set if the engine’s computer doesn’t see the coolant temp get up as high as it should after a certain period of time. The two main culprits would be a thermostat stuck open (which is better than closed!) or a faulty temp sensor. I’ll never tell anyone a cooling system service & new thermostat is a bad idea - it’s often a good idea as preventative maintenance. But a coolant temp sensor is also pretty easy to test for anyone with a digital multimeter - as GeorgeSanJose pointed out above. It’s also easy to get a basic read of actual coolant temp with an IR thermometer.

The reason that it can cause problems with how the car runs is that a colder car has to run richer - more fuel. In essence, if your car is staying too cool it is running too rich. But worse would be if it’s actually getting up to proper temp but the computer THINKS it’s cooler than it is (from a bad temp sensor). That will cause it to run poorly. How poorly would depend on how far off the temp sensor is.

Your car is about the right age for the thermostat to start to fail. Typically the thermostats fail in the open position so your engine would run cold. This has to be fixed.