2010 Cadillac Truck Escalade RWD V8-6.2L Page 1558
P1A20
DTC P0C77 or P1A20
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System
Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an
overview of the diagnostic approach.
* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure
Instructions) provides an overview of each diagnostic category.
DTC Descriptors
DTC P0C77
- Hybrid Battery System Precharge Time Too Short
DTC P1A20
- Hybrid Battery System Precharge Time Too Long
Circuit/System Description
The drive motor generator battery control module is also referred to as the battery energy control module (BECM). The drive motor generator
battery control module will diagnose its own systems and determine when a fault condition is present. Diagnostics and system status is
communicated from the drive motor generator battery control module to the hybrid powertrain control module (HPCM) through serial data. The
hybrid powertrain control module is the host controller for diagnostic trouble code (DTC) information.
The drive motor generator battery contains 3 high voltage contactors that allow the high voltage direct current (DC) batteries to be connected to the
vehicle or safely contain the DC high voltage within the drive motor generator battery assembly. The three contactor/relays are a positive high
voltage contactor, negative high voltage contactor, and the current limit relay.
The power-up sequence for the high voltage DC system occurs in the following order:
1. The drive motor generator battery control module performs a precharge test, by closing both the negative contactor and current limit relay.
Because the current limit relay routes the high voltage current through a current limit resistor, the hybrid battery terminal voltage should
increase at a steady, predictable rate.
2. When the drive motor generator battery control module observes that hybrid battery terminal voltage and hybrid battery calculated voltage
are at about the same voltage, the motor generator battery control module closes the positive contactor.
3. With both the negative and positive contactors closed, the drive motor generator battery control module opens the current limit relay.
Conditions for Running the DTC
P0C77
* Ignition voltage is 9-18 V at the drive motor generator battery control module.
* The current limit relay and negative contactor are commanded closed by the hybrid powertrain control module.
* The terminal voltage is less than 60 V prior to starting the precharge sequence.
P1A20
* Ignition voltage is 9-18 V at the drive motor generator battery control module.
* There are less than 4 hybrid battery voltage sensor faults.
Conditions for Setting the DTC
P0C77
One of the following conditions exist:
* The high voltage DC current is greater than 25 A during precharge.
* Within 20 milliseconds of the start of precharge, hybrid battery calculated voltage and powertrain inverter module terminal voltage are
already within 23 V of each other.
P1A20
140 milliseconds after the start of precharge, hybrid battery calculated voltage and hybrid battery terminal voltage are 23 V apart.
Action Taken When the DTC Sets
