5-Volt Regulator Diagnostic - P1AC8

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 hybrid control module (HCM) 5-volt regulator diagnostic employs 3 tests. The first test diagnoses the 5-volt regulator from the internal HCM hardware line. This line is switched high when the 5-volt regulator hardware detects one of the following faults: gross out of regulation, low input voltage, high input voltage, shorted load, over temperature. In the event that the 5-volt line goes high, a fail flag will be raised. The second test compares the 5-volt external reference analogue measurement with an expected range. If the analogue reading is outside of the valid range, either the 5-volt external or the supply/reference is out of regulation and a fail flag is raised. An additional test detects if the external 5-volt regulator is stuck on. At power-up, before the regulator is enabled, the regulator voltage is observed through its analogue input channel. If this reading indicates that 5 volts is present, the 5-volt regulator diagnostic is reported failed for the remainder of the trip.