Hi there, this is my first post, and normally I would post in the Newbies section, but I figured this area would be more appropriate. I have a 1998 Chevrolet Cavalier coupe, base trim, 2.2 L engine with 167,700 miles, and I need some advice pinpointing a problem. I just got this car last week. Yesterday, the check engine light came on, and the radiator fan stopped working. I went to Advance Auto Parts to get the codes scanned, and it returned five codes, which I should have written down. Out of those five codes, I remember two sets of them were the same: P0118 - Engine Coolant Temperature Circuit High Input and P0440 - Evaporative Emission Control System Malfunction. My main concern is the radiator fan not engaging, which is causing the temperature gauge to climb slightly higher than normal when I'm at a stop or in slow traffic.

Last week when I got the car, I noticed the fan wasn't spinning when the engine was warm, and my personal mechanic pinpointed the problem to the cooling fan relay, which I replaced and still works. I also removed the coolant reservoir to replace the low coolant sensor and clean out the gunk that was inside it. All the fuses are fine as well. Yesterday, we tested the cooling fan motor by turning on the A/C, and it operates normally when the compressor is engaged. Unfortunately, the A/C system has a leak at the compressor and this temporary solution will not work. With the A/C off, he unplugged the connector from the engine coolant temperature (ECT) sensor, and the fan did not engage as it should have by default. We did not remove the ECT sensor because the car was still warm, but a quick glance at it caused him to believe that it is fairly new and was recently installed. He applied a quick fix to this problem by running a wire from the fan motor to the fuse panel so that the fan engages when the ignition is on. He also used his scan tool to clear the DTC error codes.

Although this fix will work, I'm afraid that after a few days of driving the check engine light will come back on. Therefore, I have a few questions to ask. First off, what temperature should the coolant be to make the PCM engage the cooling fan? On all my previous cars, the temperature gauge needle stayed right below the halfway mark, and the fan engaged at that temperature. On the Cavalier, normal operating temperature seems to be exactly at the halfway mark, and sometimes it climbs a hair above when I'm in slow traffic or idling. Second, since I removed the coolant reservoir last week, I believe I may have introduced some air into the system. Would air in the cooling system trigger the P0118 code? If so, I may need to bleed the air out of the system. Next, why would the cooling fan not engage if I remove the connector from the ECT sensor? While my mechanic was diagnosing the problem, he removed the connector, and the temperature gauge on the dash went straight to cold. I haven't checked the connector for 5V and ground reference since I don't have a multimeter, but my assumption is that it's working. Perhaps I could replace the ECT sensor since the one installed may be faulty even though it looks fairly new. Finally, are these two codes, P0118 and P0440 related? I was told that the P0440 could just be a faulty gas cap. I'm hoping that the PCM isn't going out since that would be a costly part to replace. Anyway, I know this is a lengthy post, but I figured I would write down as much information as possible. I'll update as the days go by and see if the check engine light comes back on. If it does I will write down the codes this time. Thanks in advance.