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Old 03-03-2011, 09:36 PM   #1
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P0135 Code- Any Danger?

I work as an auto tech- I replace these O2 sensors all the time (yes, checking the wiring harness too). My own personal car just threw a P0135 error code indicating: Bank1 Sensor1 Heater Circuit Malfunction, Oxygen Sensor.

I am trying to learn here so please correct me where my understanding is wrong.
Basically the ECM throws the code if it thinks that the O2 sensor is not heating up quickly enough based on checking it against the coolant temperature. The whole purpose of this being to allow the computer to switch from open loop to closed loop operation sooner for efficiency. When the computer throws this code, the O2 sensor will still work once the vehicle is at operating temperature, but it won't do what it needs to do from a cold start.

I notice absolutely no difference in driveability, therefore I believe I am still operating in closed loop.

Now here is my question: is there any damage that can be caused by allowing this to run? We're talking about carbon deposits on the cylinders/destroying the cat as if it were a totally failed sensor- I don't believe I run this risk because I am still in closed loop and because this is my own POV I just want to make sure. Is this correct?

The reason I ask is because my tools and shop are in another city and I have work to do here so I won't be there for another two days or so (with me still driving extensively). If this were a customer, I would have no problem telling them not to worry; shows the difference in perspectives when the tables have turned.

Thanks for the help,
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Old 03-03-2011, 10:02 PM   #2
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Re: P0135 Code- Any Danger?

P0135 is set in memory when the PCM does not detect O2 sensor voltage switching above and below the bias voltage within a specified period of time after a start up. It has nothing to do with coolant temp. The oxygen sensor itself must be OK or it would have set a DTC for it. Only the heater portion of the sensor is not operating. The only problem you could expect is that it will take a longer period of time for the HO2S to heat up on its own, as a result, the PCM will remain in open loop longer. It's very doubtful you'd notice a difference in fuel mileage or perfromance.
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Old 03-03-2011, 10:19 PM   #3
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Re: P0135 Code- Any Danger?

Thanks for your input, Old Master, I really appreciate it.

However, I found a discrepancy in your statement about the coolant temperature and now I'm curious in the discrepancy. I would really value your knowledge and explanation on this. This is the information I pulled on OBDII (sorry, I don't have access to my Alldata here):

"This code refers to the front oxygen sensor on Bank 1. The heated circuit in the oxygen sensor decreases time needed to enter closed loop. As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The ECM tracks how long it takes for the oxygen sensor to begin switching. It the ECM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135."
http://www.obd-codes.com/p0135

I'm just trying to learn all I can so when I find someone knowledgeable, I pick their brain at every opportunity I get.

Thanks again,
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Old 03-03-2011, 11:10 PM   #4
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Re: P0135 Code- Any Danger?

"It has nothing to do with coolant temp." Needs a little more explanation

On each start up, all engine sensor data, (including coolant temp data) is stored in a file in the PCM. The data is stored until the drive trip is terminated, then the PCM dumps the file. There are several "cells" programmed into the PCM. Each cell contains a set of parameters to use under different operating conditions for injector pulse width, ignition timing, etc etc. The expected time frame for the HO2S to reach its operating temp is included in whichever cell is in use. The PCM does not monitor coolant temp during warm up for the purpose of timing the HO2S. That data is already in the cell and determined the instant the ignition is turned to the ON position, before the starter even engages. If the HO2S exceeds that time before it starts switching, the DTC is set.
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Old 03-03-2011, 11:16 PM   #5
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Re: P0135 Code- Any Danger?

Quote:
Originally Posted by old_master View Post
"It has nothing to do with coolant temp." Needs a little more explanation

On each start up, all engine sensor data, (including coolant temp data) is stored in a file in the PCM. The data is stored until the drive trip is terminated, then the PCM dumps the file. There are several "cells" programmed into the PCM. Each cell contains a set of parameters to use under different operating conditions for injector pulse width, ignition timing, etc etc. The expected time frame for the HO2S to reach its operating temp is included in whichever cell is in use. The PCM does not monitor coolant temp during warm up for the purpose of timing the HO2S. That data is already in the cell and determined the instant the ignition is turned to the ON position, before the starter even engages. If the HO2S exceeds that time before it starts switching, the DTC is set.
Wonderful explanation! Thank you very much for your time and knowledge. Would you recommend any books or articles on the topic/any other topics that you think may be useful for a starting auto tech?

Thank you again, I really appreciate it,
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Old 03-04-2011, 02:46 PM   #6
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Re: P0135 Code- Any Danger?

Glad to help. Most factory shop manuals (GM especially) give a pretty good explanaitons with the diagnostics for each DTC.
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