Ground Connection

Pins 24 and 25 of the engine control module are connected to ground at grounding point G7P. The ignition discharge module is also grounded at grounding point G7P.
The engine will not start unless it is connected to ground.

Sensor Ground
The crankshaft position sensor, manifold absolute pressure sensor, intake air temperature sensor, engine coolant temperature sensor and throttle position sensor are connected to ground via pin 67 of the control module.
The leads connected to the crankshaft position sensor and the leads from the oxygen sensors are also screened via pin 67 of the engine control module. The engine will not start without sensor ground.

Reference Ground
On pin 66 the ECM receives reference ground from the sensor ground lead so that it can measure the engine coolant temperature with extra precision. Driveability problems while the engine is warming up will occur if reference ground is not connected to pin 66.
The engine control module receives reference ground on pin 47 from the two heated oxygen sensors