My daughter finally got time to take the 03 Sonata with 59489 miles on it to
the dealer. I posted that I had found the P0160 code stored after the CEL
had gone out. Here's what the tech wrote on the receipt.

FOUND CODES P0056, AND P0160, FOUND THE B2/S2 02 SENSOR TO
BE OPEN CIRCUIT
OP CODES -- 39213ROA..0.40 // -- 39213RPO--..0.30
N69 // C15
REPLACED THE B2/S2 02 SENSOR

I was surprised to see that it had picked up another code, but pleased that
he replaced the sensor. What puzzles me tho is that the CEL never came back
on. Wouldn't you think that anything that serious would keep the CEL on? I
just checked for codes on a lark, not expecting to find anything.. It could
have very easily been ignored when it went out and not have come back on
until later when it was out of warranty. The tech obliviously cleared out
the codes and even tho it had been driven over a hundred miles the HO2S
monitor was still not ready, all the others had completed. I took it out
and drove it over 20 miles at hwy speed, but it still did not complete.
Hopefully the monitor will complete and the light/code will not come back.
I told here that if it does, to drive straight to the dealer even if it over
60000 miles.

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The reason the lamp went out is that the problem wasn't present during the
last three consecutive trip cycles. If the problem again returns for two
consecutive cycles, the lamp will come back on.

In fact, there's a reasonable likelihood the problem wasn't even present
when the technician did his testing. As much as good technicians don't
like it, repairing intermittent problems often requires experiential
knowledge. The language on the repair order is most likely necessary for
warranty regulations-- technically, the sensor isn't to be replaced unless
the technician can show it's defective. In most cases, this is much more
productive than the following: "The problem isn't present right now so
I've cleared the light and codes. Come back to the service department
when the lamp comes back on." Of course, if it turns out to be some sort
of oddball problem, it'll be very difficult to find.

In the scope of things, this is a minor issue. The main purpose of this
oxygen sensor is to monitor catalyst efficiency through comparison to the
B2/S1 oxygen sensor.

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