A Chrysler Driveability Case Study. Expect the unexpected
Brin shares an interesting driveability case study on a Chrysler Sebring. The symptoms are, an illuminated check engine light and a very rough running condition. Follow along to see how and why this Chrysler reacts differently than some may have experienced with similar faults on different car lines.
Keith, thank you for posting the link. I would like to discuss a finer point here as well.
At 4:45 Brin says that it is not obvious how the car computer figures out the O2 sensor temperature as no temperature sensor is provided.
Except that, technically (and the keyword is "technically"), the heater circuit IS a temperature sensor. At 18:55, the resistance of the heater element at room temperature is 4 Ohms, as per specification. At 23:17, when the heater is commanded on (car is running -- deleted), the Pico waveform shows resistance of around 14V / 1.4 A = 10 Ohm. So, it should be possible to deduce the temperature by monitoring the current through the O2 heater circuit.
Whether PCMs actually do it that way... well, does anyone know?
Thank you for your thoughts. I assumed that the PCM infers O2 sensor temperature based off of O2 sensor activity on this one but I'm not sure. I hope that others will share their thoughts as well.
Hi Brin. Sharing thoughts.... :-) My thought is that if the engineers knew what they were doing they would work for GM. hahahaha ;-)
I posted a question at Perkins below too.
I thought that the 02 sensor active command had to be done KOEO. I am also thinking according to ohms law I seem to be missing something, best guess the 02 sensor is not at room temp as the PPT states for the posted ohms specs.
Glen, thanks for the correction -- at 23:17, the car is not running, instead the heater is activated manually. Anyway, the O2 sensor will be toasty and resistance of the heater element higher.
We see cars that age daily here, and many of them do not have up to date software. The case study didn't mention checking and updating. Even without any TSB it's my understanding that Chrysler's rule is always attempt an update before replacing a PCM. I was told that by a career Chrysler guy who's son works there now too. I also saved some files the one and only time I had TechAuthority access. Rule #3 in image below. I'm sure you guys checked and/or tried it, I just thought in a lengthy in-depth case study like that, it should be mentioned.
That's a great point Geoff! Thank you for reminding me. I can't believe that I forgot to mention this. The PCM was checked and it was at the latest calibration. This is why I encourage folks to comment. Thanks again!
and what's funny is, the very next video I watched after that one, was a new DeFazio one, in which, he was showing how to check a Chrysler for update level. Eeeeery coincidence. LOL
It may be helpful to think about why OEMs take that position. In their world, cars are generally under warranty (3 years old or less). In many …es, there may not be service information available for that vehicle, initially. But most importantly, from the dealer's point of view, if they perform a procedure as directed by the OEM and it goes egg-shaped, they'll be paid warranty by the OEM. In the after-market, if it goes egg-shaped, you are the warranty.
We live in 2 different worlds.
Nice one. I would have had a hard time not getting stuck on the common ground for the heater. I realize the current tells all but I think I still would have camped on the ground for no good reason lol.
Glen Stutzman was kind enough to send some Chrysler Next Generation Training documents to me. We also spoke about the documents as I was driving in unfamiliar territory about 1420 miles from home. My hands were at the 10 and 2 position and I was watching the road as he read the document to me. After talking with him and once I reached my final destination for the night, I was able to revisit the document and it's clear now that the PCM does in fact use the heater circuit to monitor the heater performance. In my video, I said that I thought that the PCM might use the signal circuit to infer O2 temperature (once the 5 volt was pulled close to the normal 2.5-3.5 volts).
This is what the document says.
The PCM performs a voltage drop test with a 5 volt pull-up across a 10K ohm resister and the O2 heater. This information is used to verify proper operation of heater circuit and to indirectly determine the temperature of the O2 sensor. I scoped this circuit a lot on this vehicle, and I never saw evidence of this. This vehicle is of course long gone but I will keep my eye out for another one. I want to monitor that circuit. I want to catch the PCM testing for circuit faults and heater operation. Thank you Glen for sending the document and for taking the time to talk shop with me.
Many thanks to Glen for following up on this. Expect the unexpected, right?
I'm surprised to hear the pull-up resistor is as high as 10K -- this would make a very small voltage drop across the heater (several mV). Hard to measure, lots of noise to filter out... However, the value can be measured any time during the OFF period of the duty cycle, so no surprise if it is not visible on the scope with +/-20V channel range.
May be it will become visible if you add the same signal on Channel C at +/-1V or lower, perhaps with some filtering. Anyway, I'm sure you will get to the bottom of it. Thank you, Brin!