P1677 = immobiliser function deactivated
The Engine Control Module (ECM), the Powertrain Interface Module (PIM), and the Body Control Module (BCM) are integral part of the vehicle theft deterrent system. The theft deterrent system authenticates the security code programmed into each of these modules to prevent unauthorized vehicle operation. This authentication process includes the following steps:
1.When the ignition is turned ON or the door is unlocked by remote key the BCM and the key exchange security data to verify the correct key is used.
2.Once the correct key has been confirmed and the ignition is turned ON, the PIM and BCM exchange data to confirm the correct BCM and PIM is being used.
3.Once the correct key, BCM, and PIM is confirmed, the PIM and ECM exchange data to allow the vehicle to start.
4.The data exchange processes conducted use various encrypted data exchanges between each of the devices.
so its likley that the fault code isn't your issue
I'd say that its a worn mountings -check the tightness of the engine and gearbox mounts and their condition - thisis best done by using a jack to take the weight of the engine off the mountsand seeing if any cracks or splits open up in the rubber.Also check thetightness of the mounts bolts