Marv

Not that I am harping about the usual banter. That is a good thing! It is not good when you have a problem with our cars, but I wanted some technical advice.

I am revisiting my check engine light issue. Last time we discussed this the OBD II code was something like P1115, which is supposed to be an oxygen sensor (specifically, the driver's side gray plug).

So today I measured all four sensors with a DVM and all four read 2.5 to 2.7 Ohms on the white leads and open on the black and gray leads. Am I right to assume that the white leads are just heaters and the other two the actual sensor leads? They all tested the same so either they all work or one or more are out of tolerance and can not be tested the way I tested them.

So, I used contact cleaner on all four connectors and buttoned her up. Off at Autozone I had them do another OBD II read and then a reset.

I got five codes:

P1115
P0300 - Engine Misfire
P0304 - Cylinder #4 Misfire
P0305 - Cylinder #5 Misfire
P0306 - Cylinder #6 Misfire

According to the attendent at Autozone.

Does this sound like a faulty O2 sensor?

Are there other causes to the P0300 series faults that can cause a P1115 or maybe they are unreleated?

I am planning a long trip and want to get this resolved before I travel.

Thanks in advance!

geolab

Hi Marv,
At first thoughts, I see the Oxygen sensor is dead. My curiosity is not knowing what car model you have, and why it is only cylinders 4/5/6. You could always check your car with a porsche system tester to be 100% sure it is your sensor. If you have the chance to hook one, read the real value of the sensor on a warm engine, and it should vary between 0.63 - 0.92 volts. Anything below that is a jump to the nearest porsche dealer part number 993 606 116 01 - 150 euros here in Europe.
I have included both error code pages for more explanation.
Each pdf contains the error codes AND the proceedures to resolving them.
The p0300 pdf file I am including is a summary of the existing file, but the size is more than the 146kb I can include in my responses in this forum. If you want the whole, I can send it to you otherwise.
Keep me posted

george
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'97 Carrera S 100% original

Marv

Thanks a lot. This is very useful information.

Would the Porsche system tester accurately tell me the cause of the problem or would it simply do the same thing as the OBD II sensor?

From what I am reading, am I correct in that a bad O2 sensor can generate misfire faults?

It looks like the first thing I need to do is track down the P1115 fault, which would be the heater coils. Since all four measured between 2.5 to 2.7 Ohms I would asume that the sensors themselves are in good order (even though they all are on the high side of the limit).

Also, what does O2 sensor heating 1 ahead of catalytic converter - below lower threshold actully mean?

Am I correct in reading that it would point to O2 sensor 1 with the black connector (located on the driver's side)? Would it be the sensor that is installed between the exhaust port on the cylinder head and the catalytic converter?

Sorry for all the questions, but I really don't have a good road map for locations of all the components on the car, so it make finding things next to impossible. For instance, where is the ECM located?

geolab

Marv,

Porsche ST2 will tell you ERROR CODE P1115, and lets you measure the real live value of your components.
Of Course a bad O2 sensor generates misfire, especially a bad o2 sensor.
what does O2 sensor heating 1 ahead of catalytic converter - below lower threshold actually mean?
The o2 sensors are heated up to 300 degrees celcius to be able to measure O2 rate. They need 20 seconds to heat up to that temperature. (platinum filament)If the o2 sensor is faulty, it wont heat up and give an error code p1115. Read the pdf thoroughly, it is detailed inside.

There are two o2 sensors in the US Carrera models. (ALSO Turbo) Only one in the ROW
One in front of the Catalytic converter, and one after.
Part numbers are 99360611601 (before) and 99360611801 (after)

It looks your (before) one is faulty.

As for ECM, it depends what model year you have, and what Electronic Control Module you're talking about.
If you're talking about the main DME, it is underneath the driver's seat.

I hope I answered your questions. Please tell me what model car u have in the next message,
regards


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'97 Carrera S 100% original

long_beach_968

My 993 threw the P0300 series codes a while back, the exact same as the ones yours threw. Once while out of gas, two other times randomly after starting the car. the second time the light turned itself off on the way to the shop, the third time as well, I did pull the fault memory to be sure though. It has been a month now and no sign of a light, if it comes back, I will just drive it until it turns itself off again. one note though, the car has a very small vacum leak I found recently that could be the culprate.

Marv

Sorry, I meant to add that. It is a 1996 93 Carrera 2 with 46K miles and it is stock.

Then the P1115 code only gets thrown when the heater element resistance falls out of tolerance? If so, then it is 1) a faulty intermittant heater coil, 2) a faulty wire or connector between the O2 connector and the ECM, or 3) an issue with one channel of the ECM.

However, if the P1115 code can be thrown if the sensing element reports an erroneous value, then that is another story. The PDF seems to elude to the fault as a heater core issue and not the sensing element.

So, the ECM I am referring to would be the one that the sensor plug into. The PDF describd testing the line between the ECM and the sensor connector. If that test good (less than 1 Ohm), then the ECM is suspect.

geolab

The correlation between heating and sensing here is basically, in concordance.
The O2 sensor (lambda sensor in French) is a heated platinum filament that changes the value of an electrical current passing through it when exposed to different rates of oxygen.
This electrical value is interpreted by the ECM.
This filament has a lifespan relatively limited and is a common source of irregularity in the fuel/air mixing proceedure.
As a fact, the three alternatives discussed in the pdf. of causing this problem are every single possibility for the system to fail.
1- Faulty Oxygen sensor
2- Faulty electrical flux between the sensor and control unit
3- Faulty control unit.

In my personal opinion, it is very rare the Control unit or the electrical harness are faulty. I see no reason for wear in those.
The problem should be the Oxygen sensor.
If you have access to a PST2, try reading the real value of the Oxygen sensor while engine running, my guess is that it's going to read a steady 0.1 volts.
I do not know if you can do that with an OBD2 reader.
Also, if you have access to another 993, try exchanging the O2 sensor to check.


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'97 Carrera S 100% original

Marv

I should be able to simply put a DVM (Digital Volt Meter) leads on the black and gray wires and check the voltage there to confirm your guess.

I have some 30 gauge wire I can stuff into the pins and use those as "break out" wires.