Check Engine Light query

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Schurkey

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I don't understand what disconnecting the battery is supposed to accomplish.

Use the scan tool to clear all the trouble codes even if you think there aren't any. Run the engine afterwards, and it see if it will achieve closed-loop operation.

What, if any, trouble codes come back? No pending codes?

What scan tool are you using? Do you have VIN-specific operation for this vehicle, or is it working on "generic" OBD 2 settings? Does it work properly on other vehicles?
 

mr_s

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I don't understand what disconnecting the battery is supposed to accomplish.

Use the scan tool to clear all the trouble codes even if you think there aren't any. Run the engine afterwards, and it see if it will achieve closed-loop operation.

What, if any, trouble codes come back? No pending codes?

What scan tool are you using? Do you have VIN-specific operation for this vehicle, or is it working on "generic" OBD 2 settings? Does it work properly on other vehicles?

@Schurkey 'Grasping at straws' is the main focus for the battery disconnect... And predictably it made no difference whatsoever.

The scan tools - 2 different OBD2 bluetooth 'ELM327' type adapters, 2 different apps on my phone (the main one I use is Torque Pro) shows no codes unless I provoke it (such as disconnecting the ECT sensor or the MAF etc.). I can then clear these codes and they don't reappear unless I force them to. And yes, it works fine on my 2001 Jaguar XKR and my 2006 Saab 9-5 turbo, so I'm confident it is reporting correctly.

I'm not sure what you mean by 'Do you have VIN-specific operation for this vehicle'? Can you please explain what you mean?

Thinking out loud now - given that the PCM is clearly seeing the correct coolant temp sensor reading, what else is there that could report to it that 'something' isn't up to temperature? Is it possible that the new o2 sensors have faulty heating elements in them, and they aren't heating up sufficiently? Could that report to the scan tool 'open loop due to insufficient temp'?

And thanks again for responding, it all helps!
 
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Schurkey

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I don't know "Torque Pro"; or any of the other "software" OBD systems.

I know that SOME "OBD 2" setups have to have the vehicle VIN-number entered into the tool in order to access the full range of OBD 2 diagnostics. Some connect but only use "Generic" OBD 2 diagnostics. The "Generic" OBD 2 is better than nothing, but far less useful than VIN-specific.

Do the O2 sensors report seemingly-valid numbers? IF so, yes, I have a suspicion that you're looking at a failed PCM.
 

mr_s

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Thanks for explaining @Schurkey that makes sense.

The o2 sensors do indeed report sensible numbers (0.7-0.8v at idle and if I blip the throttle they go to 0.1 or so).

I keep leaning towards the PCM being the issue, do you happen to know if I can use a PCM from any 1997 Vortec 5.7, or if it needs to be coded to my truck? Still leaning towards a 0411 swap, but it depends on what I can easily get this side of the pond!
 

mr_s

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Ordered a replacement 'stock' ECU from a '97 K2500, so I'll report back when it arrives and is fitted...
 

mr_s

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Well, the new ECU went in this evening and..... it's sorted - went into closed loop mode as soon as it got up to temperature. Happy days!

The only trouble now is that the EGR has been blanked off (and I can't see any connectors for it in the area...) and it sometimes throws a check engine light. Can't pass the annual MOT test with a check engine light! Ah well, add it to the list...!!

Thanks to everyone that helped, it's all appreciated - even if it's just to confirm my own thoughts.
 
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