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Q: 1997 s500 oil light on and engine makes a ticking noise at idle.. /code p0115

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Oil light on and engine makes a ticking noise at idle/ code p0115. Car oil pressure gose up and down

My car has 190000 miles.
My car has an automatic transmission.

It looks like you have separate issues. Code P0115 has to do with the coolant temperature circuit. This code can be set due do a thermostat that is not opening or closing fully or even a bad coolant temperature sensor. A certified technician can connect a scanner to the diagnostic port and observe the values being registered by the coolant temperature sensor. This can help the technician isolate the exact cause.

As for the ticking sound, this can be caused by a few issues. Most commonly with high mileage on this particular engine, this can be caused by a stretched timing chain, worn timing chain guides, or even a weak timing chain tensioner. This can also cause oil pressure fluctuation. The ticking and oil pressure fluctuation can also be caused by worn, clogged, or collapsed valve lifters. With the scanner connected to the diagnostic port, the technician can observe the engine timing. If the timing is varying beyond specifications, this can indicate a [timing chain replacement](https://www.yourmechanic.com/services/timing-chain-replacement0 may be necessary to correct the issue.

Have a certified technician inspect the vehicle for these faults as soon as possible.

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