2006 Saab 9-3 1.8i OBD codes p0136 and p0141 - O2 sensor issue. Mystery! (maybe)

Hi!

I got the p0136 (sensor circuit B1S2) and p0141 (sensor heater circuit B1S2) error codes on my 2006 Saab 9-3 1.8i. This was present when I bought the car dirt cheap a month ago.

As of last month I obviously was a parts changer and just bought a new sensor. Coincidentally it was the same excact sensor as the one the previous owner had installed. The one he installed was fairly new as well, looked barely used. Its a cheap Delphi sensor but it is supposed to be compatible with this car and engine.
The b1s1 sensor looks to be a Delphi as well (same wire colors).

With my cheap scan tool reading live data, the B1S1 sensor fluctuate as it should. With the new and "old" sensor the B1S2 is steady at. 0.000 volts but occasionally hits 0.015 volts which still is as if it doesnt produce any voltage…

So I started digging. I saw one of ScannedDanners videos on YT regarding checking if there was short or open from ECM to harness or error with the ECM to/from the O2 sensor. As per the video I performed the following two tests:

So while reading live data (ignition on, engine off) I licked one finger and kept it on battery positive and licked the other finger touching the O2 signal connector on the harness.
(I did this test and the following tests on both the b1s1 harness and b1s2 harness to check if there were similarities and/or discrepancies between the working and non working O2 sensor / harness.)

The voltage went from 410 mv to 1.275 volts on both harnesses. As it should according to Danner.

Next I shorted the O2 signal connector on harness to ground. The voltage dropped from steady 410 mv to 0 volts on both harnesses. Also as it should according to Danner.

So then I checked all 4 connectors on both harnesses to see what voltage they were providing with the engine running. I started the engine and quickly checked the heater circuit. It showed 13.79 volts on both power supply and ground for heater. Same on both harnesses.

I checked the signal wire and ground for the signal circuit, the ground showed 13.79 volts for both harnesses. The signal wire for the b1s1 (working sensor and harness) fluctuated between ca. .300 volts and around .580 volts.

The signal wire for the b1s2 showed steady .319 volts one time and the next time I checked it was steady at .296 volts.

Im no mechanic, but to me all this points in direction of the O2 sensor not being compatible with the car or that the ECM doesnt "process" the signal correctly or something of that nature…? Or am I dead wrong? Is the other tests I can do to find the problem if this isnt it?


All replies are really appreciated!

"I started the engine and quickly checked the heater circuit. It showed 13.79 volts on both power supply and ground for heater. Same on both harnesses"

Was voltage on ground side also holding steady or was it fluctuating (indicating it's being pulsed) and your voltmeter is too slow to catch it?

I would verify the heater circuit integrity at the harness side by substituting a test light, then clear the codes, then run the engine. The light should be flashing intermittently for this test.

Connect test light to battery positive and touch the female terminal, harness side, and one of the two should be a pulsing ground from the PCM.

EDIT: female or male side I don't know, just do the tests harness side with sensor unplugged.. oh and clear the codes between tests but to be thorough.

Thanks for the reply!

Voltage hit 13.9 volts but to be honest I only monitored it for 3-4 seconds. Its not an advanced multimeter though and might not pick up quick fluctuations.

So if the voltage is not in pulses (ie test light not flashing, but being constantly lit) there is an error with the PCMs signal and ground to the sensor?

Ill try to clear codes and run the mentioned test with a test light tomorrow.

"So if the voltage is not in pulses (ie test light not flashing, but being constantly lit) there is an error with the PCMs signal and ground to the sensor?"

I am focused on the heater circuit only, not the signal circuit as you've already proved the signal wire is good with your finger licking touch test lol.

So if the control side of heater circuit is not in pulses (ie test light not flashing, but being constantly lit) there is an error with the PCMs heater circuit, aka ground wire from the sensor to the PCM. The wire could be shorted to ground, if test light is constantly lit (not the case because you saw voltage on both wires remember) or open in the control wire, loose connection, or worst case, a PCM driver problem (driver inside PCM is faulty and stuck OFF, never giving the heater a ground).

The gist is, the voltage feed should be constant on one terminal .The other terminal goes to the PCM and the PCM will provide a pulsing ground. Basically you may have an broken wire on the heater circuit.

Thanks Leeroy.

I have now checked mentioned ground wire with a test light.

Btw: the ground/control wire for the heater circuit divides (or is spliced, I guess it depends from which end your see it from ) into two separate ground wires which is connected to two pins at the pcm.

I probed the connector by the sensor, the wire right before it’s divided, right after the splice and at the two pins at the pcm.

At all check points, including the PCM pins, the test light flashed/pulsed for about 10-15 seconds before being constantly lit.
Before each probe I deleted the DTCs.
I never probed with the sensor connected though.

I’m sorry for being ignorant, but should this wire be pulsating constantly even with the sensor disconnected?

Any more ideas to what the error might be?

I’m sorry for being ignorant, but should this wire be pulsating constantly even with the sensor disconnected?

Yes this is normal because your computer thinks your test light (a resistor) is the sensor's heater. My thinking is the computer is pulsing the test light (fake heater) waiting for a sensor signal to come alive. It doesn't see a signal, so it provides a full ground making the test light lit constantly, to make the sensor heat up faster.

Now, I'm wondering if the PCM doesn't like the resistance of the new sensor or it's off from a factory sensor and that's why it's setting this DTC.

Can you measure the resistance of the old and new sensor's heater circuit? My gut feeling is they're going to be the same.

Let me be clear I'm not sure if the test light should be staying lit after the flashing, those were just my guesses. I am at the limit of my understanding as well.

Maybe do a a thorough visual inspection of the harness as far back as you can for signs of damage.

Ok, thanks again for the great info.

I can do that tomorrow, but as I said, the old one and the new one is excactly the same make and model. So I expect they will provide the same resistance. And I suspect the previous owner replaced the original one that eventually went bad with the “old one” and the issue then occurred.

So maybe I should just fork out some more cash for a new and different sensor
Frustrating.

Well, I have not installed a new sensor yet. Someone was kind enough to scan my ECM with Tech2. The codes that came up was more precisely P0141 04 and p0136 01.

I downloaded the workshop information system (WIS) to be able to go through all the tests required.

Tech 2 gave the following info on the DTCs:

P0141 04:
"O2 sensor heater circuit open (bank 1 sensor 2)" - "Output stage diagnosis in control module (open current circuit)".

First step was to test voltage between PIN3 on harness (power supply to heater) and ground. Should show above 11V, which it did.

Second step was to unplug ECM an check voltage across PIN1 (heater ground) on harness and ground. Should be below 0.3 volts which it was.

Third step was to check resistance between PIN 1 and ground. Should show above 500 kOhm. Couldnt get a reading ("OL" on multimeter) so guess that was good as it shows no short to ground.

Fourth step was to check resistance between PIN 1 and PIN 8 and 51 on the ECM. Showed 0 ohms as it should.

End of tests in the WIS.


P0136 01:
O2 sensor circuit high voltage (bank 1 sensor 2) - "the control module has identified a malfunction on the current circuit with an internal assessment logic."

First step was to check live data with the sensor unconnected. It shows 410 mv and not 450 mv as it should.

The second step was the check voltage on harness PIN2 (signal wire) to ground. Multimeter showed 422 mv. According to WIS its supposed to be 400-450 mv.

Third step was to check PIN 4 (signal ground) to ground. Reading should be below 0.3v, which it was.

Fourth step was to check resistance between PIN 4 and ground with the ECM unplugged. Reading supposed to be above 500 kOhm. Multimeter couldnt give me a reading - "OL", again good.

Fifth step was to check resistance between PIN4 and PIN24 on the ECM. It showed 0 ohm. Good as well.

End of tests in the WIS.


Does the BIAS voltage at 410 mv instead of 450 mv (first check regarding p0136) represent an issue or is it within spec even though the WIS says it should be 450 mv?

So with all the test Ive done, does this indicate that the ECm doesnt fancy the new O2-sensors resistance as you pointed out as a possible source of the problem Leeroy? Or If theres a problem with the ECM itself, shouldnt Tech2 be able to pick this up?