Circuit Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The crankshaft position (CKP) sensor provides a signal to the powertrain control module (PCM) which generates the 12x and 2x signals. The starter/generator control module (SGCM) shall calculate the speed and position of the engine by using the 12x and 2x signals generated by the PCM. The SGCM shall use the engine speed message sent by the PCM over the GMLAN bus to verify the speed calculated using the 12x and 2x signals. The 12x and 2x signals shall be used to calculate the engine position.

The 12x signal is a pulsed signal calculated by the PCM to represent engine speed. This is a square wave where 12 pulses represent one 360 degrees revolution of the engine. This signal is used by the SGCM to determine engine speed.

The 2x signal is a pulsed signal calculated by the PCM to represent engine speed. This is a square wave where 2 pulses represent one 360 degrees revolution of the engine. This signal is used to determine engine speed.

Both signals are used to determine engine position.

When these signals are out of synchronization, a DTC will set.

The SGCM has 2 discrete crank signal circuits inputs to calculate engine position. One is hard wired and one is a signal on the GMLAN bus. This acts as a back-up system in the event that one signal is interrupted, the engine will be able to start and run although a DTC will set.

The following DTCs are for faults with the engine speed signal circuits, and internal failures within the SGCM.

P0616 Starter Relay Control Circuit Low Voltage
P0617 Starter Relay Control Circuit High Voltage
P2617 Crankshaft Position Signal Output Circuit
P0725 Engine Speed Circuit