P1A20
DTC P0C77, P0C78, or P1A20
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P0C77
- Hybrid Battery System Precharge Time Too Short
DTC P0C78
- Hybrid Battery System Precharge Time Too Long
DTC P1A20
- Battery Energy Control Module Hybrid Battery System Precharge time Too Long
Typical Scan Tool Data
Circuit/System Description
The drive motor generator battery contains 3 high voltage contactor relays that allow the high voltage (HV) direct current (DC) batteries to be connected to the vehicle. The three relays are a positive HV contactor relay, negative HV contactor relay and pre-charge contactor relay. These relays close and open in a certain sequence controlled by the battery energy control module (BECM). The circuits are monitored by both the BECM and the hybrid powertrain control module (HPCM) located inside the power inverter module. The BECM measures this voltage on the terminal voltage sense wires. The HPCM monitors this voltage from the HV DC bus inside the drive motor generator control module.
To start the sequence of power up for the HV DC bus, the HV negative and HV pre-charge relay turn on first, this allows the HV DC circuit to limit current through a pre-charge current limit resistor. The voltage then travels through the 300 volt DC cables up to the power inverter module (PIM). Once the HPCM reads 95 percent of available buss voltage it sends a contactor command signal to the BECM to close the HV positive contactor relay, The BECM then closes the HV positive contactor relay and then opens the pre-charge relay. The sequence times and voltage levels are monitored by both the BECM and HPCM. If the time limit or voltage value during a particular sequence is out of the specified range, the BECM and/or HPCM will set these DTCs. DTC P1A20 is monitored and set by the BECM. DTCs P0C77 and P0C78 are monitored and set by the HPCM.
Conditions for Running the DTC
P0C77 and P0C78
* Accessory voltage is 9-18 volts at the HPCM.
* Contactors commanded closed by the HPCM.
* The terminal voltage measurement must be less than 60 volts prior to starting the precharge sequence in order for this DTC to run.
P1A20
* The vehicle power mode is RUN.
* Accessory voltage is 9-18 volts at the BECM.
* Less than 4 hybrid battery voltage sensor faults.
Conditions for Setting the DTC
P0C77
The HPCM detects Precharge time more than 110 ms and hybrid battery current is more than 25 amps or the HPCM measures 95 percent of the hybrid battery calculated voltage in less than 20 ms.
P0C78
The HPCM detects less than 200 volts on the HV DC bus 500 ms after the precharge sequence starts.
P1A20
150 ms after the precharge sequence starts, the BECM detects more than a 23 volt difference between the hybrid battery terminal voltage and the hybrid battery calculated voltage.
Action Taken When the DTC Sets
DTCs P0C77, P0C78, and P1A20 are Type C DTCs.
Conditions for Clearing the DTC
DTCs P0C77, P0C78, and P1A20 are Type C DTCs.
Diagnostic Aids
Check the calculated hybrid battery voltage and make sure it is more than 200 volts. A low voltage hybrid battery can set DTC P0C78.
The pre-charge resistor is rated at 12 ohms. If 11-13 ohms is measured across the HV+ and HV- at the positive contactor relay, the pre-charge relay could be stuck closed. If DTCs P1A20 and P0C78 are both set the fault is in the drive motor generator battery. A stuck precharge or positive contactor relay combined with a stuck closed negative High voltage contactor relay will also set DTC P1AE7.
Special Tools
* EL-48569 Terminal Covers
* EL-48900 HEV Safety Kit
Circuit/System Verification
1. Ignition ON, engine OFF, connect a scan tool. Monitor the contactor system status and the hybrid battery terminal voltage value in the BECM data list.
2. Ignition OFF, after the relay contactors click open, verify the contactor system status displays OPEN, and the hybrid battery terminal is less than 15 volts.
3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records data.
Circuit/System Testing
Important: You must perform the Circuit/System Verification first.
1. Verify if DTC P0C76 was set.
^ If DTC P0C76 was set, diagnose DTC P0C76 first.
2. Verify if DTC P0C78 was the only precharge DTC set.
^ If DTC P0C78 was the only precharge DTC set, Check for less than 200 volts in hybrid battery, If more than 200 volts replace the HPCM.
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" isolation gloves rated at 1000V with leather protectors
- Visually and functionally inspect the gloves before use.
- Wear the isolation 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.
Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling.
3. Remove the drive motor generator battery upper cover.
4. Inspect and test the HV DC cables and connection points from the hybrid battery positive and negative output terminals to the HV positive, HV negative contactor relays, from the HV positive, HV negative and precharge contactor relays to the output HV DC terminals of the drive motor generator battery for an open/high resistance condition.
^ If an open/high resistance condition is found on the HV cables or connection points, replace the faulty component.
5. Inspect and test the HV 300 volt DC cables and connection points from the battery pack to the TPIM assembly for an open/high resistance condition.
^ If an open/high resistance condition is found on the HV cables or connection points, then replace the HV 300 volt DC cable.
6. Connect the 12 volt battery.
7. Disconnect the inline connector X10 at the HV negative contactor relay.
8. Test for infinite resistance across the HV+ and HV- terminal connections.
^ If less than the specified value, replace the HV negative contractor relay.
9. Test for less than 1 ohm of resistance at X10 terminal 2 and ground.
^ If the resistance is more than the specified value, then repair the open/high resistance condition.
10. Connect a test lamp between X10 terminal 1 and ground. The test lamp should not illuminate.
^ If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit test normal, replace the BECM.
11. Command the HV negative relay ON, with scan tool. The test lamp should illuminate.
^ If the test lamp does not illuminate, test the control circuit for a short to ground, or an open/high resistance. If the control circuit tests normal, replace the BECM.
12. Disconnect the inline connector X7 at the HV positive contactor relay.
13. Test for infinite resistance across the HV+ and HV- terminal connections.
^ If less than the specified value, replace the HV positive contractor relay.
14. Test for less than 1 ohm of resistance at X7 terminal 2 and ground.
^ If the resistance is more than the specified value, then repair the open/high resistance condition.
15. Connect a test lamp between X7 terminal 1 and ground. The test lamp should not illuminate.
^ If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit test normal, replace the BECM.
16. Command the HV positive relay ON, with scan tool. The test lamp should illuminate.
^ If the test lamp does not illuminate, test the control circuit for a short to ground, or an open/high resistance. If the control circuit tests normal, replace the BECM.
17. Disconnect the inline connector X9 at the precharge contactor relay.
18. Test for infinite resistance across the HV+ and HV- terminal connections.
^ If less than the specified value, replace the HV precharge contractor relay.
19. Test for less than 1 ohm of resistance at X9 terminal 1 and ground.
^ If the resistance is more than the specified value, then repair the open/high resistance condition.
20. Disconnect the inline connector X8 at the precharge contactor relay.
21. Connect a test lamp between X8 connector terminal 5 and ground. The test lamp should not illuminate.
^ If the test lamp illuminates, test the control circuit for a short to voltage. If the circuit test normal, replace the BECM.
22. Command the HV precharge contactor relay ON, with scan tool. The test lamp should illuminate.
^ If the test lamp does not illuminate, test the control circuit for a short to ground, or an open/high resistance. If the control circuit tests normal, replace the BECM.
23. Test for 11-13 ohms between the HV- terminal at the precharge contactor relay and the HV- terminal at the positive contactor relay.
^ If the value is not within the specified range, replace the HV precharge contactor current limiting resistor.
24. If all circuits test normal, replace the drive motor generator control module (DMCM).
Component Testing
Important: You must perform the Circuit/System Verification first.
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" isolation gloves rated at 1000V with leather protectors
- Visually and functionally inspect the gloves before use.
- Wear the isolation 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.
Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling.
1. Remove the drive motor generator battery upper cover.
2. Disconnect X7 at the HV positive contactor relay, and X10 at the HV negative and positive contactor relays.
3. With a DMM measure between 20-30 ohms between terminals 1 and 2 at X7 and X10 on the component harness side.
^ If the values are not within the specified range, replace the faulty HV relay contactor.
4. Disconnect inline connectors 5 and 6 at the pre-charge relay.
5. With a DMM measure between 55-75 ohms between terminals 5 and 6 at the pre-charge relay.
^ If the value is not within the specified range, replace the pre-charge contactor relay.
7. Test for infinite resistance across the between the HV+ and HV- terminals on the HV positive contactor relay.
^ If the resistance is less than infinite, replace the HV positive contactor relay.
8. Test for infinite resistance across the between the HV+ and HV- terminals on the HV negative contactor relay.
^ If the resistance is less than infinite, replace the HV negative contactor relay.
9. Test for infinite resistance across the between the HV+ and HV- terminals on the HV precharge contactor relay.
^ If the resistance is less than infinite, replace the HV precharge contactor relay.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair. Verification Tests
* Drive Motor Battery Negative High Voltage Contactor Relay Replacement
* Drive Motor Battery Positive High Voltage Contactor Relay Replacement