Saturn Service Light mystery

99 Saturn SL1 with 146k miles. A few weeks ago during my daily commute, the service light came on. A few moments later the light came on again for a few moments and went off again. I pulled off, checked all my fluid levels and didn’t notice anything out of the ordinary. I have replaced the thermostat and the EGR in this car before. On driving home from work one day, the service light came on and as I sat in stop-and-go traffic the temperature started to creep up and up until I turned the heater on full blast. I have noticed that the service light only comes on when the RPM are at 2700 or higher for longer than 1 minute. After the engine cycles back down to a lower RPM the service light turns off again. The helpful ppl at Autozone couldn’t locate a code because at rest the light isn’t on. I rely on the expertise (such as it is) of the Cartalk community to provide me with a resolution. Thanks in advance.

Check to see if the cooling fan is working. If the fan isn’t working the engine will heat up while idling or in stop-and-go traffic.

I can’t explain the lack of codes. If the light was on there should be a stored code.

The code readers that the parts stores use can’t retrieve what are called history codes. History codes are codes that the computer stores when the Service Engine light comes on and then turns back off. Find someone who has a scanner capable of retrieving history codes.


There are CEL ( Check Engine Lights) and SEL ( Service Engine Lights)

 That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

I’m told by the ppl at autozone that the service light is just going off because the car needs to be serviced, which is probably true.

However, the heat issue is still presenting itself. Could it be a faulty thermostat?

These cars are notorious for having bad coolant temp sensors and pigtails. You just need a real scanner to diagnose this, not a code checker.

I’d still like to see you answer mcparadise’s question. Is the cooling fan working or what?

Have you checked the coolant level?

Of course a thermostat problem might be involved. But the thermostat is only one part of the system. Check the fan.

And either open the owners manual or find one or whatever and get to know the lights on your dash. There are lights that are about maintenance due. Then there is the light that turns on when something malfunctions (the “malfunction indicator lamp” (MIL) which might say “service engine soon” or “check engine” or maybe even some other things). Perhaps it is your MIL lighting up with code indicating a cooling fan circuit malfunction.

But don’t guess. Figure out what your lights mean. Check the operation of your cooling fan and coolant level. Get the codes read if the light is the MIL.