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Re: Failed readiness status on my smog check.

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I had a P1118 and did not replace the O2 sensor (bank 2, driver side, post-cat) about 1550 miles ago. I cleaned the MAF, replaced the air filter and reset the memory. CEL never returned, but I have not checked the readiness since then. Reading more about it, I probably should have replaced the O2 sensor back then due to the readiness issue.

I have 2 spare new pre-cat O2 sensors. I believe that the sensors are universal, except for the harness length. I found that the post-cat harness is 16.7", the pre-cat is 10.8". I got under my car, looked and felt the routing of the post-cat harness. It appears that the excess length is coiled up.

Has anyone ever used a pre-cat sensor in the post-cat sensor location? Experience any problems with the installation? I have a short time to correct and get re-checked for smog. Plus, at least $100 to get a new one in 3 to 5 days.

2000 S, ~60k on the post-cat sensor. California car.

Thanks.



Edited 1 time(s). Last edit at 03/03/2018 11:30AM by Tony in Whittier. (view changes)
I have a similar problem, Replaced both the post-cat O2 Sensors. No fault codes but cannot get the system "ready" fro state inspection. Have driven over 200 mils and followed various 'cycle drives" but no success as yet
P1118 - Oxygen sensor heating after TWC, bank 2.

This suggests the heater in the sensor is not functioning properly and this suggests the sensor is just defective.

The pre and post converter sensors -- at least this is the case with my 2002 Boxster and I think from 2000 to 2002 -- are as best I can tell identical other than one (I don't recall which one) has a longer electrical lead. The sensor with the long lead might be used in place of the sensor with the shorter lead but one should ensure the extra lead length is secured so it can't hang down and brush up against the hot exhaust or rub or get damaged by road debris. Even just hanging loose over time can have the wiring wiggling around in the air blast and the wiring can suffer from fatigue and fail.

IIRC -- it has been years -- the sensor with the short lead is just long enough to reach the connector with the sensor installed in the manifold but the lead is not long enough to follow the factory routing. The lead ends up running against the block IIRC which is no good.

It is important the sensor wiring leads use the factory routing and wire harness holders to prevent any movement of the wiring. So unless you are comfortable with electrical lead routing my advice is to get the right sensors with the proper length leads.

(Years ago I tried to adapt sensors with a short lead to work where a long lead sensor would normally go. The problem is one can't solder the sensor lead to a section of another lead to make a longer lead. The solder can introduce a voltage bias that interferes with the DME's interpretation of the voltage signal. I ended up using special crimp connectors that were filled with a special fluid that when the connector was crimped would cause this fluid to seep out and form a moisture tight seal around the crimped connection. But I decided this just added another failure point and elected to use genuine Porsche O2 sensors with the right length leads out of the box.)

If you are not seeing the converter readiness monitor being set to complete the odds are this is being held up as the DME tries to sort out the bad sensor's behavior. The sensor may not be bad all the time only intermittently bad. That the error code points to the heater and if the heater is intermittent the sensor may go from hot enough to not hot enough then back again and so on. Thus the sensor is bad often enough to interfere/delay the DME from completing the O2 readiness test and moving on to the converter readiness test but not bad often enough for the DME to log an O2 sensor error. If your OBD2 tool is sophisticated enough you might (might) see a pending error code related to the suspected bad O2 sensor.

When it comes to CA smog tests I don't like to risk a failure. Back in January 2015 when my Turbo was throwing a P0135 error code as soon as I got home I booked the car in and had 4 new sensors installed. (The original sensors had 132K miles on them.) The car was past due for a smog test required for registration. I had been away on family business a long time nearly a month and while I was able to mail in the registration fee the registration process wouldn't be complete until the CA DMV had proof the car passed smog.

Similarly and more recently when my Boxster starting manifesting O2 sensor errors -- I can't recall the error number now -- I just had all 4 replaced. The old sensors were not original but had been in service for a lot of miles, maybe nearly 200K miles.
Good news. I have been very worried the last few weeks, since my registration postmark is due on 4/2/18.

Based on Marc's recommendation, I used the new 2 spare O2 sensors and I bought 2 more (post-cat). I had my mechanic install them. He reset the OBD memory and after 3 or 4 cold start & drive cycles the secondary readiness cleared (That and the catalyst remained after a 1 or 2 drive cycles). The catalyst readiness still remained. That was the same exception as when I had my failed smog test. I wondered if it would ever clear. Well, after 8 cold start and drive cycles (135 miles since reset), the readiness was complete. I have driven it more, but not with a fully cold engine.

I took the car in and it passed the smog test. What a relief. I didn't want to register the car as inoperable (if I needed a catalytic converter or two).
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