Hi

I have a cheap, crappy OBD-2 code reader tool. I was wondering, since I've never used a better tool, can the higher-end code readers tell you whether the PCM is running in closed-loop or open-loop?

What about those sweet realtime-data monitor units, do they specify this?

Would it be possible I wonder to build a circuit that interfaces with the PCM to tell whether it's running in closed-loop or open-loop? It would be neat to mount an LED on the dash somewhere that shows this

Thanks

 

Yes, today's higher-end units can monitor engine operating parameters, including the 02 sensor feedback to the PCM.

FYI, an OBD-II vehicle equipped with heated 02 sensors will go into closed-loop approximatly 30-60 seconds after cold start.

 

cool

i want to specifically know that the PCM is in closed loop though for example, I just solved 2 lean codes (which means my truck was running in open loop for months). I still have a o2 sensor malfunction code which i haven't fully diagnosed. I think it has to do with the 3rd o2 sensor (the after-cat downstream one) and i have yet to replace it. since the 3rd o2 sensor doesn't effect mixture directly, i wonder whether my PCM is running in closed loop.

 

Well, to be honest I'm not exactly sure I understand what the issue is, but here's a few things to consider:

1. The 3rd (or "after-cat") O2 sensor does not affect nor have anything to do with closed-loop operation (or open-loop for that matter). It's sole purpose is to measure the efficiency of the cat converter. Put another way, if the after-cat 02 sensor is faulty, it will not prevent the system from entering into closed loop..

2. A lean condition is the not the same thing as running in open-loop, nor is open-loop some kind of default mode for a lean running engine. A lean condition can be associated with long-term fuel trim, while closed-loop operation is to be associated with short-term fuel trim. For instance, a set of P0171 and P0174 codes is an indication that the PCM's adaptive fuel strategy (long term) has reached it's programmed limits. According to the PCM, both banks are running lean. Yet, an engine that's throwing those codes can and will continue to operate in closed loop when it's suppposed to, regardless. Of course, a lean engine may not run as well in closed loop, since the the PCM can no longer compensate properly for the lean condition - hence the codes.

What year is the vehicle, btw?

 

it's a 96

interesting information there I figured that if the PCM decided to throw a CEL/MIL regarding some fuel trim matter, that it automatically went into a "drive home mode" or open loop.