$7F is indeed a negative response. A negative response frame is formated as such:
ARB ID: $XXX, B1: $0X, B2: $7F, B3: $SS, B4: $NN, B5: $XX, B6: $XX, B7: $00, B8: $00
Where $SS = Service Requested (in your case Mode $01) and
Where $NN = Return Code.
Here is a list of some return codes:
$11 Service Not Supported
$12 Sub Function Not Supported - Invalid Format
$22 Conditions Not Correct Or Request Sequence Error
$31 Request Out Of Range
$35 Invalid Key
$36 Exceed Number Of Attempts
$37 Required Time Delay Not Expired
It seems to me that your ECU does not support Mode $01. There is little you can do about this. You can try another ECU try $7E1-$7E7. Maybe one of them will work for you.