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Carlocutor · 09-20-2007, 08:34 PM

I would heed what michbound suggested, and that is to turn headers on (presumably you're using an ELM or ELM derivative device, in which case you would do this with the "ATH1" command). When you do this, you will likely see the positive responses coming from one ECU and the negative response (0x7f??12) coming from another ECU. The headers will show you which ECU sent the negative response. Unfortunately, I'm not sure if you can address the RPM & VIN requests directly to the ECU that responds positively (and not send to the NACK-ing ECU), at least not on an ISO9141 network (though you can address OBD requests to individual ECUs on a CAN network).

Does your ELM device show you as having OBD on ISO14230 on your vehicle?

09-20-2007, 08:34 PM	#7
Carlocutor Newbie Join Date: Aug 2007 Location: Detroit, MI Posts: 26	I would heed what michbound suggested, and that is to turn headers on (presumably you're using an ELM or ELM derivative device, in which case you would do this with the "ATH1" command). When you do this, you will likely see the positive responses coming from one ECU and the negative response (0x7f??12) coming from another ECU. The headers will show you which ECU sent the negative response. Unfortunately, I'm not sure if you can address the RPM & VIN requests directly to the ECU that responds positively (and not send to the NACK-ing ECU), at least not on an ISO9141 network (though you can address OBD requests to individual ECUs on a CAN network). Does your ELM device show you as having OBD on ISO14230 on your vehicle?