P1A20
DTC P0C77 or P1A20
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (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
* DTCs P0C77 and P1A20 are type C DTCs.
* The hybrid powertrain control module will not command the high voltage contactors closed.
Conditions for Clearing the DTC
DTCs P0C77 and P1A20 are type C DTCs.
Diagnostic Aids
Note: If the high voltage contactors opened while under high current load, replace BOTH high voltage contactors. The following conditions could cause the high voltage contactors to open while under high current load:
* A collision resulting in supplemental inflatable restraint (SIR) deployment.
* A collision that activates the high voltage circuit impact detection (HVCID) sensor.
* A high voltage circuit impact detection sensor circuit fault that occurs while the vehicle is moving.
* A loss of power or ground to the drive motor generator battery control module while the vehicle is moving.
The precharge time can be affected by the following:
* A long precharge time may be caused by an open 125 A fuse in the manual disconnect lever
* A short precharge time may be caused by a positive high voltage contactor stuck.
* A negative high voltage contactor stuck closed will not affect the precharge sequence.
A long or short precharge time may cause any of the following;
The drive motor generator battery control module will start a precharge wait timer after failing 2 consecutive precharge events. The contactors will not close until the precharge wait time has timed out.
Reference Information
Schematic Reference
* Hybrid Energy Storage Schematics ()
* Hybrid Controls Schematics ()
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Drive Motor Battery System Description ()
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Special Tools
* EL-48458 HV Precharge Tester
* EL-48569 Terminal Covers
* EL-48900 HEV Safety Kit
Circuit/System Testing
Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.
The High Voltage Disabling procedure will perform the following tasks:
* Identify how to disable high voltage.
* Identify how to test for the presence of high voltage.
* Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.
Failure to follow the procedures exactly as written may result in serious injury or death.
1. Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling ().
2. Disconnect the air conditioning control module terminal X4 B+ (300 V) and terminal X5 ground (300 V).
3. Test for infinite resistance between the terminals listed below and ground;
* X4 B+ (300 V) cable
* X5 ground (300 V) cable
• If less than the specified value, replace the air conditioning control module assembly.
4. Test for greater than 50k ohm between the B+ (300 V) terminals X4 and ground (300 V) X5.
• If less than the specified range, test the circuits for a short between the circuits. If the circuits test normal, replace the air conditioning control module assembly.
5. Connect the EL-48458 at the drive motor generator power inverter module. Refer to the EL-48458 installation procedure located in High Voltage System Diagnosis (EL-48458) ().
Note: Install a manual disconnect lever with a verified good fuse or a new manual disconnect lever.
6. Install the manual disconnect lever.
7. Connect the 12 V battery.
8. Ignition ON, attempt to precharge the high voltage system by moving the high voltage contactor relay switch on the tester to the closed position. Verify that the hi-voltage greater than 60 V LED does not illuminate.
• If the LED illuminates, replace the drive motor generator power inverter module.
Note: The following tests require wearing personal protection equipment (PPE) gloves.
9. Ignition OFF, remove the EL-48458. Refer to the removal procedure located in High Voltage System Diagnosis (EL-48458) ().
10. Ignition OFF, disconnect the X1 B+ (300 V) and X2 ground (300 V) cables from the drive motor generator battery.
11. Test for infinite resistance between the terminals listed below and ground
* X1 B+ (300 V) cable
* X2 ground (300 V) cable
• If less than the specified value, replace the high voltage cables.
12. Ignition ON, command the negative and positive contactors and the current limit relay ON and OFF with a scan tool. Listen for the contactors and relay to turn ON and OFF.
• If the negative contactor, positive contactor or the current limit relay does not turn ON and OFF, refer to High Voltage Contactor/Relay Malfunction ().
13. Ignition OFF, visually inspect and test the drive motor generator battery internal high voltage DC cables and connections for a short to ground or an open/high resistance condition.
• If a short to ground or an open/high resistance condition is found on the high voltage cables or connection points, replace the drive motor generator battery cable.
14. If all the circuit tests normal, replace the drive motor generator battery assembly.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Drive Motor Battery Negative Relay Cable Replacement ()
* Drive Motor Battery Positive Relay Cable Replacement ()
* Drive Motor Battery Positive and Negative Cable Replacement ()
* Drive Motor Battery 300-Volt Positive and Negative Cable Replacement ()
* Control Module References (Programming and Relearning) for drive motor generator battery control module, drive motor generator power inverter module, air conditioning control module assembly replacement, setup and programming