Limp home mode


May 24, 2001
On a recent drive 1986 GN seemed to go into Limp home mode. At home I hooked up a scan tool, but could not get connectivity with the ecm. I wrongly thought ecm was defective and replaced it. Could not get connectivity with new ecm. What am I missing? I have not driven the car since. Any ideas would be appreciated.
Thank you
Last month , My alternator was dying & I drove ~ 42 miles in Limp Home mode ? Had it rebuilt to 120 Amps & WahLaaa ! Could be dirty , Corroded connections ? Just Say'n
limp is triggered by the white bypass wire to the ignition module going open
if the white bypass wire to the ignition module is sound ...its usually the ignition module that has failed and opened the connection in the module

problem with LIMP HOME MODE is it defers fueling based on the small calpack chip in the ecm which is setup for stock 28# injectors , so if your injectors are larger the fueling will be way off (rich)
see gnntype code 42