P1A20
DTC P1A20
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
DTC Descriptor
DTC P1A20
- Battery Energy Control Module Hybrid Battery System Precharge Time Too Long
Circuit/System Description
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 drive motor generator control module through serial data. The drive motor generator control module is the host controller for diagnostic trouble code (DTC) information.
The drive motor generator battery contains 2 high voltage (HV) contactors and a current limit relay, also called the precharge relay. The contactors allow the high voltage DC batteries to be connected to the vehicle or safely contain the DC high voltage within the drive motor generator battery assembly. The two contactors are a positive HV contactor, negative HV contactor , and current limit relay. These contactors close and open in a certain sequence and are controlled by the drive motor generator battery control module. The control circuit for the contactors use a buss bar attached to the circuit board and the drive motor generator battery control module supplies a ground to turn them on and off individually. The drive motor generator battery control module monitors the control circuit voltage to these contactors and 12 V reference circuit internal to the control module to determine if the circuit is open by comparing the two voltage readings. If the drive motor generator battery control module detects 2 consecutive failed high voltage precharge events, a precharge wait time is activated by the drive motor generator battery control module. This precharge wait time limit is to allow the precharge circuit internal to the drive motor generator battery assembly to cool down. The precharge wait time counts down in seconds and is displayed on the scan tool.
The power-up sequence for the HV DC system occurs in the following order:
1. The drive motor generator battery control module performs a precharge test, by closing both the negative and current limit relays. Because the current limit relay routes the HV current through a current limit resistor, the hybrid battery terminal voltage increases 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 drive 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.
The drive motor generator battery control module calculates a total hybrid battery voltage based upon internal hybrid battery voltage sensor. The drive motor generator battery control module measures the actual voltage at the hybrid battery terminals and compares this value to the calculated voltage.
The drive motor generator battery control module measures the actual voltage within the drive motor generator power inverter module (PIM) and compares this value to the calculated voltage. The time it takes for terminal voltage to equal hybrid battery calculated voltage is measured and recorded. If the precharge event does not occur as expected, a DTC will set.
If the drive motor generator battery control module detects 2 consecutive failed high voltage precharge events, a precharge wait time is activated by the drive motor generator battery control module. This precharge wait time limit is to allow the precharge circuit internal to the drive motor generator battery assembly to cool down. The precharge wait time counts down in seconds and is displayed on the scan tool. The contactors will not close until the precharge wait time has timed out.
Conditions for Running the DTC
* The accessory voltage is 9-18 V at the drive motor generator battery control module.
* The ignition is ON.
Conditions for Setting the DTC
After waiting 140 milliseconds after the start of precharge, hybrid battery calculated voltage and hybrid battery terminal voltage are still within 90% of each other.
Action Taken When the DTC Sets
* P1A20 is a type C DTC.
* The drive motor generator control module will not command the HV contactors closed.
Conditions for Clearing the DTC
P1A20 is a type C DTC.
Diagnostic Aids
* An open 135 A fuse in the manual disconnect lever may cause this DTC to set.
* The current limit resistor is rated at 10 Ohms.
* A negative HV contactor stuck closed will not affect the precharge sequence.
* A positive HV contactor stuck closed will also set DTC P0C77.
* The drive motor generator battery control module will start a precharge wait timer after failing 2 consecutive precharge events.
Reference Information
Schematic Reference
Hybrid Energy Storage Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Drive Motor Generator Battery Description (Drive Motor Generator Battery Identification Information)
Drive Motor Generator Control Module Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Special Tools
* EL-48458 HV Precharge Tester
* 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.
Danger: Before working on any high voltage system, be sure to wear the following Personal Protection Equipment:
* Safety glasses with appropriate side shields when within 50 feet of the vehicle, either indoors or outdoors
* Certified and up-to-date Class "0" Insulation gloves rated at 1000V with leather protectors
- Visually and functionally inspect the gloves before use.
- Wear the Insulation gloves at all times when working with the high voltage battery assembly, whether the system is energized or not.
Failure to follow the procedure exactly as written may result in serious injury or death.
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. Verify that DTC P01AF, P0C77, P1A0E, P1A0F, P1A47, P0ABC, or P0ABD is not set, and that no drive motor generator control module DTCs is set.
• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code Descriptions).
2. Verify the 135 A HV fuse in the manual disconnect lever is not open.
• If fuse is open, inspect the high voltage cables internal to the battery assembly for proper connections. If all circuits test normal, replace the drive motor generator battery assembly.
3. Connect the EL-48458 at the drive motor generator power inverter module (PIM). Refer to the EL-48458 installation procedure located in High Voltage System Diagnosis (EL-48458) (High Voltage System Diagnosis (EL-48458)).
4. Ignition ON, attempt to precharge the HV system by moving the HV contactor switch on the tester to the closed position. Verify that the hi-voltage circuit LED for hi-voltage greater than 60 V does not illuminate.
• If the LED illuminates, replace the drive motor generator power inverter module.
5. Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling (High Voltage Disabling).
6. Remove the EL-48458 . Refer to the removal procedure located in High Voltage System Diagnosis (EL-48458) (High Voltage System Diagnosis (EL-48458)).
7. Inspect and test the HV 300 V positive and negative DC cables and connection points between the drive motor generator battery and the drive motor generator power inverter module (PIM) assembly, and the cable connections at both components for an open/high resistance.
• If an open/high resistance condition is found on the HV cables or connection points, replace the drive motor battery 300 V positive and negative cable.
8. Inspect and test the drive motor generator battery internal HV DC cables and connections for an open/high resistance.
• If an open/high resistance condition is found on the HV cables or connection points, replace the drive motor generator battery assembly.
9. Connect the 12 V battery.
10. Disconnect the X4 harness connector at the drive motor disconnect control module.
11. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 7 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the drive motor generator battery control module.
12. Ignition OFF, connect a test lamp between the B+ circuit terminal 7 and the control circuit terminal 8.
13. Ignition ON, with a scan tool command the HV positive contactor open and closed several times. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit tests normal, replace the drive motor generator battery disconnect control module.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the drive motor generator battery disconnect control module.
14. If all circuits test normal, replace the drive motor generator battery control module.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Drive Motor Battery Disconnect Control Module Replacement (Drive Motor Battery Disconnect Control Module Replacement)
* Drive Motor Battery 300-Volt 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 replacement, setup and programming