456 GTA "Open Loop" on Bank 1 EOBD Facile

Evening, I have a 456GTA 1997 with low miles (11k) a garage “queen”, which I have owned for many years. It’s had its fair share of known 456 problems over the years but I have tried to be proactive and perform preventive maintenance, with grateful thanks to everyone on this forum.

So, to the problem at hand; I would be thankful for any guidance: my “Bank 1 ECU (offside) is showing “open loop- due to system fault” when using EOBD facile diagnostics on a PC with ELM327 USB to check. I am connecting via the ALDL connector in the passenger footwell (RHD) and can see both ECUs xx14 and xx17 and connect to them.


According to EOBD neither of them has any stored DTCs. The bank 1 is xx17 and Bank 2 is xx14 addresses. Bank 2 is operating in the normal closed loop.

The reason I discovered this was that we have an annual car test in the UK called an MOT in which the emissions are checked, it failed on the CO emissions. Up until this point I was unaware of any problems, apart from a cold start issue which has been with the car for a couple of years, in which bank 2 always starts and Bank 1 lags behind by approx. 20 secs. There is no sign of this issue when warm and it has just been annoying. I assumed it was an open loop or air pump problem but never really had time to investigate it fully.

After failing the MOT I brought the car back home and it ran fine on the way home. I connected my PC and looked at the two ECU’s. The readings on the pre O2 sensor seemed strange compared to bank 2 (aka xx14 ECU) and I concluded it must be that O2 sensor. I ordered a new “universal” sensor Bosch 0258986507 and whilst I was waiting, I swapped the ECUs over, the open loop stayed with Bank 1 it has eliminated the ECU as the issue.

The MOT garage then fitted the O2 sensor to Bank 1 pre-O2 sensor and the car duly passed its MOT – happy days? However, I re-ran the diagnostics once home no DTCs as before but Bank 1 is still in “open loop”?

So the question is: is this “open loop” a known declared mode of operation with master and slave Motronic 5.2 ECUs ( I suspect not) that one declares itself master and runs both calculations? I see (when comparing ECU sensor info) that Bank 1 sees the air temp at – 40 c because there is no air temp sensor for Bank 1 intake on the passenger side (RHD) - crossflow. Also, Bank 2 ECU does not know the coolant temperature from the data presented so there are some peculiar modes with twin 5.2's.

Is it the case that "open loop" on the slave is normal for twin Motronic 5.2 systems? I strongly suspect it's not. That being the case what circumstances cause open loop – The garage (general garage) replaced the O2 sensor for that “Bank 1” and the O2 sensors are well known- to cause “open loop” then I guess it’s the MAF (whose readings look similar to the other bank). What is the criteria for 5.2 Motronic to declare “open loop”? does it take some cycles to clear "open loop" status?

I have not used EOBD Facile fully before and know it's not as good as the SD1 diags etc. I have "Launch" diagnostics which has the relevant 456 diags but cannot find the ECUs etc. when EOBD can?


Many thanks for any advice, I have data from the diagnostics but will not swamp you with it, unless requested. Mike.

 

Thanks so much for taking the time to reply. Yes, I agree with sensors - I am unsure of what conditions are necessary to go into "open loop" with the 5.2 motronic. I am aware of the engine running to obtain values etc. I note that the the two ecus with only power on (no engine running) that one is "open loop" and the other is "closed loop" so I assume these conditions are latched. When the engine starts they remain in their respective conditions. Of note is that on swapping the ECU over the "open loop" ecu stayed open loop on power on but cleared with an engine start and "open loop" moved to the other ECU - thus eliminating the ECU. I *think* that the engine coolant temp and air temp missing are just twin motronic quirks, but happy to be corrected.
My next step is to collect data streams when running from the two ecus and compare to see if there are any abnormalaties. I will report back.

I suspect, but do not know, that EOBD Facile maybe not entirely compatible with say reading DTCs - I think I must have some but I am not seeing them.

Anybody had any luck with Launch Easy Diag V2.0 on ALDL conectors on 5.2 ECUs - it lists my car and 5.2 ECU but no connection, it would be useful to have a another diagnostic suite.

Thanks again. Mike.

 

@redwedge thanks so much for taking the time to post this, very helpful. Sorry for my tardy response here. We have just returned from a 4k-mile trip across Europe in my 456 and I was up to my ears to prepare the car and try to solve this "open loop" problem before departure. So starts a story but the conclusion is that it is now SOLVED! A week before my trip I started preparing the car and regarding the "open loop" problem I started looking at fuel and wanted to check fuel pressure but my fuel rails were blanked off where the connections should be? So as part of the preparation, the fuel filters were changed with an instant improvement in the starting and idling. I was on to something here - but the "open loop" stayed on. I decided to pull the pumps and inspect, to be honest, I was quite taken back, the green gasket on the passenger side RHD was trapped and nicked where clamped - I had suffered from a "fuel smell" for many years since the car had a major with a specialist who replaced both pumps. More troubling was when removing the (driver's side RHD) the banjo nut was completely loose on top of the pump - presumably spraying fuel back into the tank and not to the engine! The pumps themselves did not have the standard supports but were wrapped in rubber - which had started to disintegrate in the ethanol-based fuel. I replaced the pumps and used ethanol-tolerant pipes and Fabio's pump mounts. The difference after completing this work was that the car sounded and ran 100% better with improved performance all around! However, the "open loop" remained - I tried doing a reset with the EODB software on the 5.2s - no change then swapped various components from left to right banks - no change, restored parts. Then I swapped out the air pump relay (which I had discounted before because it was common to both banks) and "presto" the "open loop" was gone! I am still troubled by the logic of air pump issue being the cause of the “open loop” on “bank 1” but I ran out of time and started our trip. Happy to report 4k miles completed which is a third of all the mileage this car has ever done. The car behaved faultlessly over that mileage – averaged just under 19 mpg and used 500ml of oil. No sign of any fuel smell! Happy to hear any theories on why the air pump would only affect one bank – maybe as @redwedge suggested I performed some reset unknown to me. Thanks again.