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RSLyrick · 11-16-2024

I didn't remember that the fan would start when A and B are shorted

Good to know. Then, the question for JT_n_CT_90_ZR1 is, are the fans also starting when A and B are not shorted, ignition ON ?

I think the display is showing Err in the two following scenarios :

1) A and B jumped (ECM diagnostic) :

The CCM will display Err when attempting to display ECM DTCs for the LT5 engine. CCM display and clearing of ECM DTCs is available only for the LT1. Use the Tech 1 for ECM DTCs on the LT5.

2) A and G jumped (CCM diagnostic) :

If there is a communications problem between the ECM or EBTCM and, the CCM, the speedometer will display Err when the CCM is trying to communicate with the ECM or EBTCM.

Question for JT_n_CT_90_ZR1, do you also see Err when you do not short any diagnostic pin ?

Try to retrieve any CCM and ECM codes with the procedure which I described before.

I agree with Jeff and Todd, let us know if any kind of work has been done on your ECM :

- Repair job (also if you see a kind of seal / label which states that is has been remanufactured at some point)

- Calibration Chip installation (if you don't know, maybe you could open the ECM mem-cal door and take a picture of the currently used chip). As Todd mentionned, double check that is properly seated and that the connector is not bent.

- Anything that you may have done that could have caused damages to the ECM (removal, jump start, battery polarity inversion...). I know a guy who did accidently a reverse polarity connections on his LT1, so far all the car ECUs (ECM, CCM, ABS...) were functional so I doubt that it would have caused damaged to yours if you did it, but still, let us know.

Opening the ECM to look for damages is a bit more tricky procedure than for your CCM but feasible if you are familiar with handling fragile stuff...but try to retrieve diagnostic codes for the CCM and ECM first. This can really help.

If damages happened on your CCM, similar damaged may have happened on your ECM as well. Either caused by anything that you may have done or the CCM failure itself led to the ECM failure due to their shared interfaces (UART). I have seen this in other cars ECUs where interfaces were poorly protected, one failed leading to damages to the other one...

So, you got no fuel pumps running and no check engine light when ignition is ON without diagnostic enabled. This sounds like an ECM issue but too early to confirm.

No crank : starter toasted or starter relay not triggered by the CCM (security issue then or something else)

Get us some DTCs if any !

11-16-2024	#24
RSLyrick Join Date: Oct 2023 Location: Germany Posts: 42	Re: I think I?m in deep 💩 I didn't remember that the fan would start when A and B are shorted Good to know. Then, the question for JT_n_CT_90_ZR1 is, are the fans also starting when A and B are not shorted, ignition ON ? I think the display is showing Err in the two following scenarios : 1) A and B jumped (ECM diagnostic) : The CCM will display Err* when attempting to display ECM DTCs for the LT5 engine. CCM display and clearing of ECM DTCs is available only for the LT1. Use the Tech 1 for ECM DTCs on the LT5.* 2) A and G jumped (CCM diagnostic) : If there is a communications problem between the ECM or EBTCM and, the CCM, the speedometer will display Err* when the CCM is trying to communicate with the ECM or EBTCM.* Question for JT_n_CT_90_ZR1, do you also see Err when you do not short any diagnostic pin ? Try to retrieve any CCM and ECM codes with the procedure which I described before. I agree with Jeff and Todd, let us know if any kind of work has been done on your ECM : - Repair job (also if you see a kind of seal / label which states that is has been remanufactured at some point) - Calibration Chip installation (if you don't know, maybe you could open the ECM mem-cal door and take a picture of the currently used chip). As Todd mentionned, double check that is properly seated and that the connector is not bent. - Anything that you may have done that could have caused damages to the ECM (removal, jump start, battery polarity inversion...). I know a guy who did accidently a reverse polarity connections on his LT1, so far all the car ECUs (ECM, CCM, ABS...) were functional so I doubt that it would have caused damaged to yours if you did it, but still, let us know. Opening the ECM to look for damages is a bit more tricky procedure than for your CCM but feasible if you are familiar with handling fragile stuff...but try to retrieve diagnostic codes for the CCM and ECM first. This can really help. If damages happened on your CCM, similar damaged may have happened on your ECM as well. Either caused by anything that you may have done or the CCM failure itself led to the ECM failure due to their shared interfaces (UART). I have seen this in other cars ECUs where interfaces were poorly protected, one failed leading to damages to the other one... So, you got no fuel pumps running and no check engine light when ignition is ON without diagnostic enabled. This sounds like an ECM issue but too early to confirm. No crank : starter toasted or starter relay not triggered by the CCM (security issue then or something else) Get us some DTCs if any ! Last edited by RSLyrick; 11-16-2024 at 12:32 PM.