Lexus 3.5L A/F Heater Control
I'm hoping someone here can help me get my head wrapped around this Lexus I had in today. C.E.L on, with the trouble codes P0051 & P2197, both related to Bank2Sensor1 Air/Fuel Sensor. I ended up replacing the sensor and my problems were fixed.
My question comes from me trying to get a waveform of the ground path signal from the PCM before I changed the sensor. No matter what I tried I couldn't get a pattern at all. Plug the new sensor in and viola! I get the one I've attached. Is it possible that the PCM would shut down the ground path driver for the heater circuit when It detects a fault with the heating element?
Thanks for any help!
Matthew, here is a question to think about: if the heater burnt up and is “open”, where would then voltage come from to be shown on your scope? By the way, which model of Rigol scope is that?
Thank you for your reply Dmitriy. I thought the same thing while trying to capture this. I decided to use battery voltage to determine the PCM's ability to ground the circuit. Am I wrong with my thought process here? The scope I'm using is a Hantek 1008 I found on Amazon, I hadn't heard of the Rigol brand until you mentioned it. It's been good to me so far. I'm still "wetting my feet" with…
Battery voltage as in through a jumper wire or incandescent test light? The latter one? If you used a test light and still no pattern then, yeah, likely the ECM decided to cease control until the code is reset. One thing that puzzles me on your capture: when amperage is high, the voltage is also high — does not bode well with the description as the ground-switched control, no? Rigol‘s mention…
Wouldn't the voltage and amperage follow each other? Can you elaborate on your thinking here? Thanks
I wouldn’t be able to explain this better than Matthew Shanahan: youtu.be/4YC3mwcTQfA
Hi Dmitriy, current probe is directional. Maybe he has it installed backwards.
Yeah! Rigol’s 1054Z love that 4 channel scope , nothing can touch it at $399.
Yep! The ECM will absolutely shut down the heater driver in response to a detected circuit fault. The trick is to install a substitute load and clear the fault, KOEO. Start it up and the driver will work briefly before resetting the fault.
Thanks Tyler! My mind went to some ignition misfires that would shut down injector operation to save catalyst damage.
Dimitry's response is great, makes you think, but how I do those heaters, like dimitry said if it's open you won't see it I use my scope and use a test light to load the circuit, then you will be able to see the control.
Yes some vehicles look for a ground or voltage before activating the the heater circuit. If you run across this again and want to make sure the computer is ok. hook test light up to simulate the heater circuit. Sometimes you have to clear the code also.
Doing a bypass test on a … oxygen sensor for whatever reason is a pain. This is what I know. The ECM will shut the circuit off if it sees an open circuit, a shorted circuit, or amperage that just isn't within spec. So substituting with a test light will still have the ECM shutting off the circuit. I've tried many times without success. But even if you unplug the oxygen sensor, and…