Intermittent Oil Light
2010 Cobalt - intermittent oil light 2.2L
I've got a weird one here and I'm out of ideas.
About 2 months ago, I was on a short errand a block from home when my dash alarm chimed 4 times. I had never heard 4 beeps before, so I had no idea what it was. I looked at the dash, but there were no lights on or messages displayed.
This pattern persisted for the next 2 weeks. I drove 250 miles on Memorial Day without incident. Then the following Saturday, I was heading up a freeway ramp when I got the 4 chimes.
This time, the oil light was on. I found that at cruising speed, it went out, but when I accelerated, it turned on again. I babied it home and checked the oil. The dipstick says it's full.
I have 103K miles on the car (had it since it was new) and it has no history of burning oil.
On Sunday, I drove one mile without incident. On the return trip 2 hours later, the light was on steady when accelerating or at idle, but turned off at minimal throttle.
Monday morning, I took it to my mechanic. He diagnosed the problem as a faulty oil pressure sending unit. Replacing it fixed the problem - for 8 days. Then I started getting the same symptoms again.
So I started gathering more information about when and where the problem occurs. With two exceptions, I have never gotten a warning beyond the first 3 miles of driving. Those exceptions were about 10 miles in and I was on an incline.
I made a 250 mile trip last week and another 200 mile one this week. The blinking light occurred in EXACTLY the same place - a 6% grade at highway speeds.
There are no symptoms indicating that the oil pressure is actually low - no overheating even with summer temperatures. The scouting report is that the oil pump rarely fails on this engine.
The error is less likely to occur when the engine is cold. It may happen more than once in the first 3 miles. If I make a stop (short or long) it may happen again during the next few miles.
Sometimes I get a chime and a light, other times I get one but not the other. I had about a week without alarms following the 250 mile trip, but now alarms have returned.
There is some more than anecdotal evidence that an uphill or downhill stretch of road aggravates the problem. This may suggest that the oil level sensor is the culprit. But why did the alarms go away after replacing the pressure sensor?
Is the replacement pressure sensor defective? That's an outside possibility, but it's a stretch of the imagination.
Some friends have suggested a wiring or connector problem. But if that's the case, why does driving a few miles cure it?
I bought an OBDII reader - no codes.